| Message ID | 20250404181443.1363005-4-joannelkoong@gmail.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | fuse: remove temp page copies in writeback | expand |
Hi Joanne, On 4/5/25 2:14 AM, Joanne Koong wrote: > In the current FUSE writeback design (see commit 3be5a52b30aa > ("fuse: support writable mmap")), a temp page is allocated for every > dirty page to be written back, the contents of the dirty page are copied over > to the temp page, and the temp page gets handed to the server to write back. > > This is done so that writeback may be immediately cleared on the dirty page, > and this in turn is done in order to mitigate the following deadlock scenario > that may arise if reclaim waits on writeback on the dirty page to complete: > * single-threaded FUSE server is in the middle of handling a request > that needs a memory allocation > * memory allocation triggers direct reclaim > * direct reclaim waits on a folio under writeback > * the FUSE server can't write back the folio since it's stuck in > direct reclaim > > With a recent change that added AS_WRITEBACK_INDETERMINATE and mitigates > the situations described above, FUSE writeback does not need to use > temp pages if it sets AS_WRITEBACK_INDETERMINATE on its inode mappings. > > This commit sets AS_WRITEBACK_INDETERMINATE on the inode mappings > and removes the temporary pages + extra copying and the internal rb > tree. > > fio benchmarks -- > (using averages observed from 10 runs, throwing away outliers) > > Setup: > sudo mount -t tmpfs -o size=30G tmpfs ~/tmp_mount > ./libfuse/build/example/passthrough_ll -o writeback -o max_threads=4 -o source=~/tmp_mount ~/fuse_mount > > fio --name=writeback --ioengine=sync --rw=write --bs={1k,4k,1M} --size=2G > --numjobs=2 --ramp_time=30 --group_reporting=1 --directory=/root/fuse_mount > > bs = 1k 4k 1M > Before 351 MiB/s 1818 MiB/s 1851 MiB/s > After 341 MiB/s 2246 MiB/s 2685 MiB/s > % diff -3% 23% 45% > > Signed-off-by: Joanne Koong <joannelkoong@gmail.com> > Reviewed-by: Jingbo Xu <jefflexu@linux.alibaba.com> > Acked-by: Miklos Szeredi <mszeredi@redhat.com> Overall this patch LGTM. Apart from that, IMO the fi->writectr and fi->queued_writes mechanism is also unneeded then, at least the DIRECT IO routine (i.e. fuse_direct_io()) doesn't need fuse_sync_writes() anymore. That is because after removing the temp page, the DIRECT IO routine has already been waiting for all inflight WRITE requests, see # DIRECT read generic_file_read_iter kiocb_write_and_wait filemap_write_and_wait_range # DIRECT write generic_file_write_iter generic_file_direct_write kiocb_invalidate_pages filemap_invalidate_pages filemap_write_and_wait_range The DIRECT write routine will also invalidate the page cache in the range that is written to, so that the following buffer write needs to read the page cache back first. The writeback following the buffer write is much likely after the DIRECT write, so that the writeback won't conflict with the DIRECT write (i.e. there won't be duplicate WRITE requests for the same page that are initiated from DIRECT write and writeback at the same time), which is exactly why fi->writectr and fi->queued_writes are introduced. However it seems that the writeback won't wait for previous inflight DIRECT WRITE requests, so I'm not much sure about that. Maybe other folks could offer more insights... Also fuse_sync_writes() is not needed in fuse_flush() anymore, with which I'm pretty sure. The potential cleanup for fi->writectr and fi->queued_writes could be offered as following separate patches (if any). > --- > fs/fuse/file.c | 360 ++++------------------------------------------- > fs/fuse/fuse_i.h | 3 - > 2 files changed, 28 insertions(+), 335 deletions(-) > > diff --git a/fs/fuse/file.c b/fs/fuse/file.c > index 754378dd9f71..91ada0208863 100644 > --- a/fs/fuse/file.c > +++ b/fs/fuse/file.c > @@ -415,89 +415,11 @@ u64 fuse_lock_owner_id(struct fuse_conn *fc, fl_owner_t id) > > struct fuse_writepage_args { > struct fuse_io_args ia; > - struct rb_node writepages_entry; > struct list_head queue_entry; > - struct fuse_writepage_args *next; > struct inode *inode; > struct fuse_sync_bucket *bucket; > }; > > -static struct fuse_writepage_args *fuse_find_writeback(struct fuse_inode *fi, > - pgoff_t idx_from, pgoff_t idx_to) > -{ > - struct rb_node *n; > - > - n = fi->writepages.rb_node; > - > - while (n) { > - struct fuse_writepage_args *wpa; > - pgoff_t curr_index; > - > - wpa = rb_entry(n, struct fuse_writepage_args, writepages_entry); > - WARN_ON(get_fuse_inode(wpa->inode) != fi); > - curr_index = wpa->ia.write.in.offset >> PAGE_SHIFT; > - if (idx_from >= curr_index + wpa->ia.ap.num_folios) > - n = n->rb_right; > - else if (idx_to < curr_index) > - n = n->rb_left; > - else > - return wpa; > - } > - return NULL; > -} > - > -/* > - * Check if any page in a range is under writeback > - */ > -static bool fuse_range_is_writeback(struct inode *inode, pgoff_t idx_from, > - pgoff_t idx_to) > -{ > - struct fuse_inode *fi = get_fuse_inode(inode); > - bool found; > - > - if (RB_EMPTY_ROOT(&fi->writepages)) > - return false; > - > - spin_lock(&fi->lock); > - found = fuse_find_writeback(fi, idx_from, idx_to); > - spin_unlock(&fi->lock); > - > - return found; > -} > - > -static inline bool fuse_page_is_writeback(struct inode *inode, pgoff_t index) > -{ > - return fuse_range_is_writeback(inode, index, index); > -} > - > -/* > - * Wait for page writeback to be completed. > - * > - * Since fuse doesn't rely on the VM writeback tracking, this has to > - * use some other means. > - */ > -static void fuse_wait_on_page_writeback(struct inode *inode, pgoff_t index) > -{ > - struct fuse_inode *fi = get_fuse_inode(inode); > - > - wait_event(fi->page_waitq, !fuse_page_is_writeback(inode, index)); > -} > - > -static inline bool fuse_folio_is_writeback(struct inode *inode, > - struct folio *folio) > -{ > - pgoff_t last = folio_next_index(folio) - 1; > - return fuse_range_is_writeback(inode, folio_index(folio), last); > -} > - > -static void fuse_wait_on_folio_writeback(struct inode *inode, > - struct folio *folio) > -{ > - struct fuse_inode *fi = get_fuse_inode(inode); > - > - wait_event(fi->page_waitq, !fuse_folio_is_writeback(inode, folio)); > -} > - > /* > * Wait for all pending writepages on the inode to finish. > * > @@ -886,13 +808,6 @@ static int fuse_do_readfolio(struct file *file, struct folio *folio) > ssize_t res; > u64 attr_ver; > > - /* > - * With the temporary pages that are used to complete writeback, we can > - * have writeback that extends beyond the lifetime of the folio. So > - * make sure we read a properly synced folio. > - */ > - fuse_wait_on_folio_writeback(inode, folio); > - > attr_ver = fuse_get_attr_version(fm->fc); > > /* Don't overflow end offset */ > @@ -1005,17 +920,12 @@ static void fuse_send_readpages(struct fuse_io_args *ia, struct file *file) > static void fuse_readahead(struct readahead_control *rac) > { > struct inode *inode = rac->mapping->host; > - struct fuse_inode *fi = get_fuse_inode(inode); > struct fuse_conn *fc = get_fuse_conn(inode); > unsigned int max_pages, nr_pages; > - pgoff_t first = readahead_index(rac); > - pgoff_t last = first + readahead_count(rac) - 1; > > if (fuse_is_bad(inode)) > return; > > - wait_event(fi->page_waitq, !fuse_range_is_writeback(inode, first, last)); > - > max_pages = min_t(unsigned int, fc->max_pages, > fc->max_read / PAGE_SIZE); > > @@ -1181,7 +1091,7 @@ static ssize_t fuse_send_write_pages(struct fuse_io_args *ia, > int err; > > for (i = 0; i < ap->num_folios; i++) > - fuse_wait_on_folio_writeback(inode, ap->folios[i]); > + folio_wait_writeback(ap->folios[i]); > > fuse_write_args_fill(ia, ff, pos, count); > ia->write.in.flags = fuse_write_flags(iocb); > @@ -1638,7 +1548,7 @@ ssize_t fuse_direct_io(struct fuse_io_priv *io, struct iov_iter *iter, > return res; > } > } > - if (!cuse && fuse_range_is_writeback(inode, idx_from, idx_to)) { > + if (!cuse && filemap_range_has_writeback(mapping, pos, (pos + count - 1))) { > if (!write) > inode_lock(inode); > fuse_sync_writes(inode); > @@ -1835,38 +1745,34 @@ static ssize_t fuse_splice_write(struct pipe_inode_info *pipe, struct file *out, > static void fuse_writepage_free(struct fuse_writepage_args *wpa) > { > struct fuse_args_pages *ap = &wpa->ia.ap; > - int i; > > if (wpa->bucket) > fuse_sync_bucket_dec(wpa->bucket); > > - for (i = 0; i < ap->num_folios; i++) > - folio_put(ap->folios[i]); > - > fuse_file_put(wpa->ia.ff, false); > > kfree(ap->folios); > kfree(wpa); > } > > -static void fuse_writepage_finish_stat(struct inode *inode, struct folio *folio) > -{ > - struct backing_dev_info *bdi = inode_to_bdi(inode); > - > - dec_wb_stat(&bdi->wb, WB_WRITEBACK); > - node_stat_sub_folio(folio, NR_WRITEBACK_TEMP); > - wb_writeout_inc(&bdi->wb); > -} > - > static void fuse_writepage_finish(struct fuse_writepage_args *wpa) > { > struct fuse_args_pages *ap = &wpa->ia.ap; > struct inode *inode = wpa->inode; > struct fuse_inode *fi = get_fuse_inode(inode); > + struct backing_dev_info *bdi = inode_to_bdi(inode); > int i; > > - for (i = 0; i < ap->num_folios; i++) > - fuse_writepage_finish_stat(inode, ap->folios[i]); > + for (i = 0; i < ap->num_folios; i++) { > + /* > + * Benchmarks showed that ending writeback within the > + * scope of the fi->lock alleviates xarray lock > + * contention and noticeably improves performance. > + */ > + folio_end_writeback(ap->folios[i]); > + dec_wb_stat(&bdi->wb, WB_WRITEBACK); > + wb_writeout_inc(&bdi->wb); > + } > > wake_up(&fi->page_waitq); > } > @@ -1877,7 +1783,6 @@ static void fuse_send_writepage(struct fuse_mount *fm, > __releases(fi->lock) > __acquires(fi->lock) > { > - struct fuse_writepage_args *aux, *next; > struct fuse_inode *fi = get_fuse_inode(wpa->inode); > struct fuse_write_in *inarg = &wpa->ia.write.in; > struct fuse_args *args = &wpa->ia.ap.args; > @@ -1914,19 +1819,8 @@ __acquires(fi->lock) > > out_free: > fi->writectr--; > - rb_erase(&wpa->writepages_entry, &fi->writepages); > fuse_writepage_finish(wpa); > spin_unlock(&fi->lock); > - > - /* After rb_erase() aux request list is private */ > - for (aux = wpa->next; aux; aux = next) { > - next = aux->next; > - aux->next = NULL; > - fuse_writepage_finish_stat(aux->inode, > - aux->ia.ap.folios[0]); > - fuse_writepage_free(aux); > - } > - > fuse_writepage_free(wpa); > spin_lock(&fi->lock); > } > @@ -1954,43 +1848,6 @@ __acquires(fi->lock) > } > } > > -static struct fuse_writepage_args *fuse_insert_writeback(struct rb_root *root, > - struct fuse_writepage_args *wpa) > -{ > - pgoff_t idx_from = wpa->ia.write.in.offset >> PAGE_SHIFT; > - pgoff_t idx_to = idx_from + wpa->ia.ap.num_folios - 1; > - struct rb_node **p = &root->rb_node; > - struct rb_node *parent = NULL; > - > - WARN_ON(!wpa->ia.ap.num_folios); > - while (*p) { > - struct fuse_writepage_args *curr; > - pgoff_t curr_index; > - > - parent = *p; > - curr = rb_entry(parent, struct fuse_writepage_args, > - writepages_entry); > - WARN_ON(curr->inode != wpa->inode); > - curr_index = curr->ia.write.in.offset >> PAGE_SHIFT; > - > - if (idx_from >= curr_index + curr->ia.ap.num_folios) > - p = &(*p)->rb_right; > - else if (idx_to < curr_index) > - p = &(*p)->rb_left; > - else > - return curr; > - } > - > - rb_link_node(&wpa->writepages_entry, parent, p); > - rb_insert_color(&wpa->writepages_entry, root); > - return NULL; > -} > - > -static void tree_insert(struct rb_root *root, struct fuse_writepage_args *wpa) > -{ > - WARN_ON(fuse_insert_writeback(root, wpa)); > -} > - > static void fuse_writepage_end(struct fuse_mount *fm, struct fuse_args *args, > int error) > { > @@ -2010,41 +1867,6 @@ static void fuse_writepage_end(struct fuse_mount *fm, struct fuse_args *args, > if (!fc->writeback_cache) > fuse_invalidate_attr_mask(inode, FUSE_STATX_MODIFY); > spin_lock(&fi->lock); > - rb_erase(&wpa->writepages_entry, &fi->writepages); > - while (wpa->next) { > - struct fuse_mount *fm = get_fuse_mount(inode); > - struct fuse_write_in *inarg = &wpa->ia.write.in; > - struct fuse_writepage_args *next = wpa->next; > - > - wpa->next = next->next; > - next->next = NULL; > - tree_insert(&fi->writepages, next); > - > - /* > - * Skip fuse_flush_writepages() to make it easy to crop requests > - * based on primary request size. > - * > - * 1st case (trivial): there are no concurrent activities using > - * fuse_set/release_nowrite. Then we're on safe side because > - * fuse_flush_writepages() would call fuse_send_writepage() > - * anyway. > - * > - * 2nd case: someone called fuse_set_nowrite and it is waiting > - * now for completion of all in-flight requests. This happens > - * rarely and no more than once per page, so this should be > - * okay. > - * > - * 3rd case: someone (e.g. fuse_do_setattr()) is in the middle > - * of fuse_set_nowrite..fuse_release_nowrite section. The fact > - * that fuse_set_nowrite returned implies that all in-flight > - * requests were completed along with all of their secondary > - * requests. Further primary requests are blocked by negative > - * writectr. Hence there cannot be any in-flight requests and > - * no invocations of fuse_writepage_end() while we're in > - * fuse_set_nowrite..fuse_release_nowrite section. > - */ > - fuse_send_writepage(fm, next, inarg->offset + inarg->size); > - } > fi->writectr--; > fuse_writepage_finish(wpa); > spin_unlock(&fi->lock); > @@ -2131,19 +1953,16 @@ static void fuse_writepage_add_to_bucket(struct fuse_conn *fc, > } > > static void fuse_writepage_args_page_fill(struct fuse_writepage_args *wpa, struct folio *folio, > - struct folio *tmp_folio, uint32_t folio_index) > + uint32_t folio_index) > { > struct inode *inode = folio->mapping->host; > struct fuse_args_pages *ap = &wpa->ia.ap; > > - folio_copy(tmp_folio, folio); > - > - ap->folios[folio_index] = tmp_folio; > + ap->folios[folio_index] = folio; > ap->descs[folio_index].offset = 0; > ap->descs[folio_index].length = PAGE_SIZE; > > inc_wb_stat(&inode_to_bdi(inode)->wb, WB_WRITEBACK); > - node_stat_add_folio(tmp_folio, NR_WRITEBACK_TEMP); > } > > static struct fuse_writepage_args *fuse_writepage_args_setup(struct folio *folio, > @@ -2178,18 +1997,12 @@ static int fuse_writepage_locked(struct folio *folio) > struct fuse_inode *fi = get_fuse_inode(inode); > struct fuse_writepage_args *wpa; > struct fuse_args_pages *ap; > - struct folio *tmp_folio; > struct fuse_file *ff; > - int error = -ENOMEM; > - > - tmp_folio = folio_alloc(GFP_NOFS | __GFP_HIGHMEM, 0); > - if (!tmp_folio) > - goto err; > + int error = -EIO; > > - error = -EIO; > ff = fuse_write_file_get(fi); > if (!ff) > - goto err_nofile; > + goto err; > > wpa = fuse_writepage_args_setup(folio, ff); > error = -ENOMEM; > @@ -2200,22 +2013,17 @@ static int fuse_writepage_locked(struct folio *folio) > ap->num_folios = 1; > > folio_start_writeback(folio); > - fuse_writepage_args_page_fill(wpa, folio, tmp_folio, 0); > + fuse_writepage_args_page_fill(wpa, folio, 0); > > spin_lock(&fi->lock); > - tree_insert(&fi->writepages, wpa); > list_add_tail(&wpa->queue_entry, &fi->queued_writes); > fuse_flush_writepages(inode); > spin_unlock(&fi->lock); > > - folio_end_writeback(folio); > - > return 0; > > err_writepage_args: > fuse_file_put(ff, false); > -err_nofile: > - folio_put(tmp_folio); > err: > mapping_set_error(folio->mapping, error); > return error; > @@ -2225,7 +2033,6 @@ struct fuse_fill_wb_data { > struct fuse_writepage_args *wpa; > struct fuse_file *ff; > struct inode *inode; > - struct folio **orig_folios; > unsigned int max_folios; > }; > > @@ -2260,69 +2067,11 @@ static void fuse_writepages_send(struct fuse_fill_wb_data *data) > struct fuse_writepage_args *wpa = data->wpa; > struct inode *inode = data->inode; > struct fuse_inode *fi = get_fuse_inode(inode); > - int num_folios = wpa->ia.ap.num_folios; > - int i; > > spin_lock(&fi->lock); > list_add_tail(&wpa->queue_entry, &fi->queued_writes); > fuse_flush_writepages(inode); > spin_unlock(&fi->lock); > - > - for (i = 0; i < num_folios; i++) > - folio_end_writeback(data->orig_folios[i]); > -} > - > -/* > - * Check under fi->lock if the page is under writeback, and insert it onto the > - * rb_tree if not. Otherwise iterate auxiliary write requests, to see if there's > - * one already added for a page at this offset. If there's none, then insert > - * this new request onto the auxiliary list, otherwise reuse the existing one by > - * swapping the new temp page with the old one. > - */ > -static bool fuse_writepage_add(struct fuse_writepage_args *new_wpa, > - struct folio *folio) > -{ > - struct fuse_inode *fi = get_fuse_inode(new_wpa->inode); > - struct fuse_writepage_args *tmp; > - struct fuse_writepage_args *old_wpa; > - struct fuse_args_pages *new_ap = &new_wpa->ia.ap; > - > - WARN_ON(new_ap->num_folios != 0); > - new_ap->num_folios = 1; > - > - spin_lock(&fi->lock); > - old_wpa = fuse_insert_writeback(&fi->writepages, new_wpa); > - if (!old_wpa) { > - spin_unlock(&fi->lock); > - return true; > - } > - > - for (tmp = old_wpa->next; tmp; tmp = tmp->next) { > - pgoff_t curr_index; > - > - WARN_ON(tmp->inode != new_wpa->inode); > - curr_index = tmp->ia.write.in.offset >> PAGE_SHIFT; > - if (curr_index == folio->index) { > - WARN_ON(tmp->ia.ap.num_folios != 1); > - swap(tmp->ia.ap.folios[0], new_ap->folios[0]); > - break; > - } > - } > - > - if (!tmp) { > - new_wpa->next = old_wpa->next; > - old_wpa->next = new_wpa; > - } > - > - spin_unlock(&fi->lock); > - > - if (tmp) { > - fuse_writepage_finish_stat(new_wpa->inode, > - folio); > - fuse_writepage_free(new_wpa); > - } > - > - return false; > } > > static bool fuse_writepage_need_send(struct fuse_conn *fc, struct folio *folio, > @@ -2331,15 +2080,6 @@ static bool fuse_writepage_need_send(struct fuse_conn *fc, struct folio *folio, > { > WARN_ON(!ap->num_folios); > > - /* > - * Being under writeback is unlikely but possible. For example direct > - * read to an mmaped fuse file will set the page dirty twice; once when > - * the pages are faulted with get_user_pages(), and then after the read > - * completed. > - */ > - if (fuse_folio_is_writeback(data->inode, folio)) > - return true; > - > /* Reached max pages */ > if (ap->num_folios == fc->max_pages) > return true; > @@ -2349,7 +2089,7 @@ static bool fuse_writepage_need_send(struct fuse_conn *fc, struct folio *folio, > return true; > > /* Discontinuity */ > - if (data->orig_folios[ap->num_folios - 1]->index + 1 != folio_index(folio)) > + if (ap->folios[ap->num_folios - 1]->index + 1 != folio_index(folio)) > return true; > > /* Need to grow the pages array? If so, did the expansion fail? */ > @@ -2368,7 +2108,6 @@ static int fuse_writepages_fill(struct folio *folio, > struct inode *inode = data->inode; > struct fuse_inode *fi = get_fuse_inode(inode); > struct fuse_conn *fc = get_fuse_conn(inode); > - struct folio *tmp_folio; > int err; > > if (!data->ff) { > @@ -2383,54 +2122,23 @@ static int fuse_writepages_fill(struct folio *folio, > data->wpa = NULL; > } > > - err = -ENOMEM; > - tmp_folio = folio_alloc(GFP_NOFS | __GFP_HIGHMEM, 0); > - if (!tmp_folio) > - goto out_unlock; > - > - /* > - * The page must not be redirtied until the writeout is completed > - * (i.e. userspace has sent a reply to the write request). Otherwise > - * there could be more than one temporary page instance for each real > - * page. > - * > - * This is ensured by holding the page lock in page_mkwrite() while > - * checking fuse_page_is_writeback(). We already hold the page lock > - * since clear_page_dirty_for_io() and keep it held until we add the > - * request to the fi->writepages list and increment ap->num_folios. > - * After this fuse_page_is_writeback() will indicate that the page is > - * under writeback, so we can release the page lock. > - */ > if (data->wpa == NULL) { > err = -ENOMEM; > wpa = fuse_writepage_args_setup(folio, data->ff); > - if (!wpa) { > - folio_put(tmp_folio); > + if (!wpa) > goto out_unlock; > - } > fuse_file_get(wpa->ia.ff); > data->max_folios = 1; > ap = &wpa->ia.ap; > } > folio_start_writeback(folio); > > - fuse_writepage_args_page_fill(wpa, folio, tmp_folio, ap->num_folios); > - data->orig_folios[ap->num_folios] = folio; > + fuse_writepage_args_page_fill(wpa, folio, ap->num_folios); > > err = 0; > - if (data->wpa) { > - /* > - * Protected by fi->lock against concurrent access by > - * fuse_page_is_writeback(). > - */ > - spin_lock(&fi->lock); > - ap->num_folios++; > - spin_unlock(&fi->lock); > - } else if (fuse_writepage_add(wpa, folio)) { > + ap->num_folios++; > + if (!data->wpa) > data->wpa = wpa; > - } else { > - folio_end_writeback(folio); > - } > out_unlock: > folio_unlock(folio); > > @@ -2457,13 +2165,6 @@ static int fuse_writepages(struct address_space *mapping, > data.wpa = NULL; > data.ff = NULL; > > - err = -ENOMEM; > - data.orig_folios = kcalloc(fc->max_pages, > - sizeof(struct folio *), > - GFP_NOFS); > - if (!data.orig_folios) > - goto out; > - > err = write_cache_pages(mapping, wbc, fuse_writepages_fill, &data); > if (data.wpa) { > WARN_ON(!data.wpa->ia.ap.num_folios); > @@ -2472,7 +2173,6 @@ static int fuse_writepages(struct address_space *mapping, > if (data.ff) > fuse_file_put(data.ff, false); > > - kfree(data.orig_folios); > out: > return err; > } > @@ -2497,8 +2197,6 @@ static int fuse_write_begin(struct file *file, struct address_space *mapping, > if (IS_ERR(folio)) > goto error; > > - fuse_wait_on_page_writeback(mapping->host, folio->index); > - > if (folio_test_uptodate(folio) || len >= folio_size(folio)) > goto success; > /* > @@ -2561,13 +2259,9 @@ static int fuse_launder_folio(struct folio *folio) > { > int err = 0; > if (folio_clear_dirty_for_io(folio)) { > - struct inode *inode = folio->mapping->host; > - > - /* Serialize with pending writeback for the same page */ > - fuse_wait_on_page_writeback(inode, folio->index); > err = fuse_writepage_locked(folio); > if (!err) > - fuse_wait_on_page_writeback(inode, folio->index); > + folio_wait_writeback(folio); > } > return err; > } > @@ -2611,7 +2305,7 @@ static vm_fault_t fuse_page_mkwrite(struct vm_fault *vmf) > return VM_FAULT_NOPAGE; > } > > - fuse_wait_on_folio_writeback(inode, folio); > + folio_wait_writeback(folio); > return VM_FAULT_LOCKED; > } > > @@ -3429,9 +3123,12 @@ static const struct address_space_operations fuse_file_aops = { > void fuse_init_file_inode(struct inode *inode, unsigned int flags) > { > struct fuse_inode *fi = get_fuse_inode(inode); > + struct fuse_conn *fc = get_fuse_conn(inode); > > inode->i_fop = &fuse_file_operations; > inode->i_data.a_ops = &fuse_file_aops; > + if (fc->writeback_cache) > + mapping_set_writeback_indeterminate(&inode->i_data); > > INIT_LIST_HEAD(&fi->write_files); > INIT_LIST_HEAD(&fi->queued_writes); > @@ -3439,7 +3136,6 @@ void fuse_init_file_inode(struct inode *inode, unsigned int flags) > fi->iocachectr = 0; > init_waitqueue_head(&fi->page_waitq); > init_waitqueue_head(&fi->direct_io_waitq); > - fi->writepages = RB_ROOT; > > if (IS_ENABLED(CONFIG_FUSE_DAX)) > fuse_dax_inode_init(inode, flags); > diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h > index fee96fe7887b..28a101a5c558 100644 > --- a/fs/fuse/fuse_i.h > +++ b/fs/fuse/fuse_i.h > @@ -141,9 +141,6 @@ struct fuse_inode { > > /* waitq for direct-io completion */ > wait_queue_head_t direct_io_waitq; > - > - /* List of writepage requestst (pending or sent) */ > - struct rb_root writepages; > }; > > /* readdir cache (directory only) */
On Tue, Apr 8, 2025 at 7:43 PM Jingbo Xu <jefflexu@linux.alibaba.com> wrote: > > Hi Joanne, > > On 4/5/25 2:14 AM, Joanne Koong wrote: > > In the current FUSE writeback design (see commit 3be5a52b30aa > > ("fuse: support writable mmap")), a temp page is allocated for every > > dirty page to be written back, the contents of the dirty page are copied over > > to the temp page, and the temp page gets handed to the server to write back. > > > > This is done so that writeback may be immediately cleared on the dirty page, > > and this in turn is done in order to mitigate the following deadlock scenario > > that may arise if reclaim waits on writeback on the dirty page to complete: > > * single-threaded FUSE server is in the middle of handling a request > > that needs a memory allocation > > * memory allocation triggers direct reclaim > > * direct reclaim waits on a folio under writeback > > * the FUSE server can't write back the folio since it's stuck in > > direct reclaim > > > > With a recent change that added AS_WRITEBACK_INDETERMINATE and mitigates > > the situations described above, FUSE writeback does not need to use > > temp pages if it sets AS_WRITEBACK_INDETERMINATE on its inode mappings. > > > > This commit sets AS_WRITEBACK_INDETERMINATE on the inode mappings > > and removes the temporary pages + extra copying and the internal rb > > tree. > > > > fio benchmarks -- > > (using averages observed from 10 runs, throwing away outliers) > > > > Setup: > > sudo mount -t tmpfs -o size=30G tmpfs ~/tmp_mount > > ./libfuse/build/example/passthrough_ll -o writeback -o max_threads=4 -o source=~/tmp_mount ~/fuse_mount > > > > fio --name=writeback --ioengine=sync --rw=write --bs={1k,4k,1M} --size=2G > > --numjobs=2 --ramp_time=30 --group_reporting=1 --directory=/root/fuse_mount > > > > bs = 1k 4k 1M > > Before 351 MiB/s 1818 MiB/s 1851 MiB/s > > After 341 MiB/s 2246 MiB/s 2685 MiB/s > > % diff -3% 23% 45% > > > > Signed-off-by: Joanne Koong <joannelkoong@gmail.com> > > Reviewed-by: Jingbo Xu <jefflexu@linux.alibaba.com> > > Acked-by: Miklos Szeredi <mszeredi@redhat.com> > Hi Jingbo, Thanks for sharing your analysis for this. > Overall this patch LGTM. > > Apart from that, IMO the fi->writectr and fi->queued_writes mechanism is > also unneeded then, at least the DIRECT IO routine (i.e. I took a look at fi->writectr and fi->queued_writes and my understanding is that we do still need this. For example, for truncates (I'm looking at fuse_do_setattr()), I think we still need to prevent concurrent writeback or else the setattr request and the writeback request could race which would result in a mismatch between the file's reported size and the actual data written to disk. > fuse_direct_io()) doesn't need fuse_sync_writes() anymore. That is > because after removing the temp page, the DIRECT IO routine has already > been waiting for all inflight WRITE requests, see > > # DIRECT read > generic_file_read_iter > kiocb_write_and_wait > filemap_write_and_wait_range Where do you see generic_file_read_iter() getting called for direct io reads? For direct io reads, I'm only seeing fuse_direct_IO() __fuse_direct_read() fuse_direct_io() and fuse_file_read_iter() fuse_direct_read_iter() fuse_direct_IO() / __fuse_direct_read() > > # DIRECT write > generic_file_write_iter > generic_file_direct_write > kiocb_invalidate_pages > filemap_invalidate_pages > filemap_write_and_wait_range Similarly, where do you see generic_file_write_iter() getting called for direct io writes? My understanding is that it'd either go through fuse_file_write_iter() -> fuse_direct_write_iter() or through the fuse_direct_IO() callback. > > The DIRECT write routine will also invalidate the page cache in the > range that is written to, so that the following buffer write needs to > read the page cache back first. The writeback following the buffer write > is much likely after the DIRECT write, so that the writeback won't > conflict with the DIRECT write (i.e. there won't be duplicate WRITE > requests for the same page that are initiated from DIRECT write and > writeback at the same time), which is exactly why fi->writectr and > fi->queued_writes are introduced. Where do you see fi->writectr / fi->queued-writes preventing this race? It looks to me like in the existing code, this race condition you described of direct write invalidating the page cache, then another buffer write reads the page cache and dirties it, then writeback is called on that, and the 2 write requests racing, could still happen? > However it seems that the writeback > won't wait for previous inflight DIRECT WRITE requests, so I'm not much > sure about that. Maybe other folks could offer more insights... My understanding is that these lines if (!cuse && filemap_range_has_writeback(...)) { ... fuse_sync_writes(inode); ... } in fuse_direct_io() is what waits on previous inflight direct write requests to complete before the direct io happens. > > Also fuse_sync_writes() is not needed in fuse_flush() anymore, with > which I'm pretty sure. Why don't we still need this for fuse_flush()? If a caller calls close(), this will call filp_close() filp_flush() filp->f_op->flush() fuse_flush() it seems like we should still be waiting for all writebacks to finish before sending the fuse server the fuse_flush request, no? > > The potential cleanup for fi->writectr and fi->queued_writes could be > offered as following separate patches (if any). > Thanks, Joanne > > > --- > > fs/fuse/file.c | 360 ++++------------------------------------------- > > fs/fuse/fuse_i.h | 3 - > > 2 files changed, 28 insertions(+), 335 deletions(-) > > > > diff --git a/fs/fuse/file.c b/fs/fuse/file.c > > index 754378dd9f71..91ada0208863 100644 > > --- a/fs/fuse/file.c > > +++ b/fs/fuse/file.c > > @@ -415,89 +415,11 @@ u64 fuse_lock_owner_id(struct fuse_conn *fc, fl_owner_t id) > > > > struct fuse_writepage_args { > > struct fuse_io_args ia; > > - struct rb_node writepages_entry; > > struct list_head queue_entry; > > - struct fuse_writepage_args *next; > > struct inode *inode; > > struct fuse_sync_bucket *bucket; > > }; > > > > -static struct fuse_writepage_args *fuse_find_writeback(struct fuse_inode *fi, > > - pgoff_t idx_from, pgoff_t idx_to) > > -{ > > - struct rb_node *n; > > - > > - n = fi->writepages.rb_node; > > - > > - while (n) { > > - struct fuse_writepage_args *wpa; > > - pgoff_t curr_index; > > - > > -- > Thanks, > Jingbo
On 4/10/25 7:47 AM, Joanne Koong wrote: > On Tue, Apr 8, 2025 at 7:43 PM Jingbo Xu <jefflexu@linux.alibaba.com> wrote: >> >> Hi Joanne, >> >> On 4/5/25 2:14 AM, Joanne Koong wrote: >>> In the current FUSE writeback design (see commit 3be5a52b30aa >>> ("fuse: support writable mmap")), a temp page is allocated for every >>> dirty page to be written back, the contents of the dirty page are copied over >>> to the temp page, and the temp page gets handed to the server to write back. >>> >>> This is done so that writeback may be immediately cleared on the dirty page, >>> and this in turn is done in order to mitigate the following deadlock scenario >>> that may arise if reclaim waits on writeback on the dirty page to complete: >>> * single-threaded FUSE server is in the middle of handling a request >>> that needs a memory allocation >>> * memory allocation triggers direct reclaim >>> * direct reclaim waits on a folio under writeback >>> * the FUSE server can't write back the folio since it's stuck in >>> direct reclaim >>> >>> With a recent change that added AS_WRITEBACK_INDETERMINATE and mitigates >>> the situations described above, FUSE writeback does not need to use >>> temp pages if it sets AS_WRITEBACK_INDETERMINATE on its inode mappings. >>> >>> This commit sets AS_WRITEBACK_INDETERMINATE on the inode mappings >>> and removes the temporary pages + extra copying and the internal rb >>> tree. >>> >>> fio benchmarks -- >>> (using averages observed from 10 runs, throwing away outliers) >>> >>> Setup: >>> sudo mount -t tmpfs -o size=30G tmpfs ~/tmp_mount >>> ./libfuse/build/example/passthrough_ll -o writeback -o max_threads=4 -o source=~/tmp_mount ~/fuse_mount >>> >>> fio --name=writeback --ioengine=sync --rw=write --bs={1k,4k,1M} --size=2G >>> --numjobs=2 --ramp_time=30 --group_reporting=1 --directory=/root/fuse_mount >>> >>> bs = 1k 4k 1M >>> Before 351 MiB/s 1818 MiB/s 1851 MiB/s >>> After 341 MiB/s 2246 MiB/s 2685 MiB/s >>> % diff -3% 23% 45% >>> >>> Signed-off-by: Joanne Koong <joannelkoong@gmail.com> >>> Reviewed-by: Jingbo Xu <jefflexu@linux.alibaba.com> >>> Acked-by: Miklos Szeredi <mszeredi@redhat.com> >> > > Hi Jingbo, > > Thanks for sharing your analysis for this. > >> Overall this patch LGTM. >> >> Apart from that, IMO the fi->writectr and fi->queued_writes mechanism is >> also unneeded then, at least the DIRECT IO routine (i.e. > > I took a look at fi->writectr and fi->queued_writes and my > understanding is that we do still need this. For example, for > truncates (I'm looking at fuse_do_setattr()), I think we still need to > prevent concurrent writeback or else the setattr request and the > writeback request could race which would result in a mismatch between > the file's reported size and the actual data written to disk. I haven't looked into the truncate routine yet. I will see it later. > >> fuse_direct_io()) doesn't need fuse_sync_writes() anymore. That is >> because after removing the temp page, the DIRECT IO routine has already >> been waiting for all inflight WRITE requests, see >> >> # DIRECT read >> generic_file_read_iter >> kiocb_write_and_wait >> filemap_write_and_wait_range > > Where do you see generic_file_read_iter() getting called for direct io reads? # DIRECT read fuse_file_read_iter fuse_cache_read_iter generic_file_read_iter kiocb_write_and_wait filemap_write_and_wait_range a_ops->direct_IO(),i.e. fuse_direct_IO() > Similarly, where do you see generic_file_write_iter() getting called > for direct io writes? # DIRECT read fuse_file_write_iter fuse_cache_write_iter generic_file_write_iter generic_file_direct_write kiocb_invalidate_pages filemap_invalidate_pages filemap_write_and_wait_range a_ops->direct_IO(),i.e. fuse_direct_IO() > Where do you see fi->writectr / fi->queued-writes preventing this > race? IMO overall fi->writectr / fi->queued-writes are introduced to prevent DIRECT IO and writeback from sending duplicate (inflight) WRITE requests for the same page. For the DIRECT write routine: # non-FOPEN_DIRECT_IO DIRECT write fuse_cache_write_iter fuse_direct_IO fuse_direct_io fuse_sync_writes # FOPEN_DIRECT_IO DIRECT write fuse_direct_write_iter fuse_direct_IO fuse_direct_io fuse_sync_writes For the writeback routine: fuse_writepages() fuse_writepages_fill fuse_writepages_send # buffer the WRITE request in queued_writes list fuse_flush_writepages # flush WRITE only when fi->writectr >= 0 > It looks to me like in the existing code, this race condition > you described of direct write invalidating the page cache, then > another buffer write reads the page cache and dirties it, then > writeback is called on that, and the 2 write requests racing, could > still happen? > > >> However it seems that the writeback >> won't wait for previous inflight DIRECT WRITE requests, so I'm not much >> sure about that. Maybe other folks could offer more insights... > > My understanding is that these lines > > if (!cuse && filemap_range_has_writeback(...)) { > ... > fuse_sync_writes(inode); > ... > } > > in fuse_direct_io() is what waits on previous inflight direct write > requests to complete before the direct io happens. Right. > > >> >> Also fuse_sync_writes() is not needed in fuse_flush() anymore, with >> which I'm pretty sure. > > Why don't we still need this for fuse_flush()? > > If a caller calls close(), this will call > > filp_close() > filp_flush() > filp->f_op->flush() > fuse_flush() > > it seems like we should still be waiting for all writebacks to finish > before sending the fuse server the fuse_flush request, no? > filp_close() filp_flush() filp->f_op->flush() fuse_flush() write_inode_now writeback_single_inode(WB_SYNC_ALL) do_writepages # flush dirty page filemap_fdatawait # wait for WRITE completion >> >>> --- >>> fs/fuse/file.c | 360 ++++------------------------------------------- >>> fs/fuse/fuse_i.h | 3 - >>> 2 files changed, 28 insertions(+), 335 deletions(-) >>> >>> diff --git a/fs/fuse/file.c b/fs/fuse/file.c >>> index 754378dd9f71..91ada0208863 100644 >>> --- a/fs/fuse/file.c >>> +++ b/fs/fuse/file.c >>> @@ -415,89 +415,11 @@ u64 fuse_lock_owner_id(struct fuse_conn *fc, fl_owner_t id) >>> >>> struct fuse_writepage_args { >>> struct fuse_io_args ia; >>> - struct rb_node writepages_entry; >>> struct list_head queue_entry; >>> - struct fuse_writepage_args *next; >>> struct inode *inode; >>> struct fuse_sync_bucket *bucket; >>> }; >>> >>> -static struct fuse_writepage_args *fuse_find_writeback(struct fuse_inode *fi, >>> - pgoff_t idx_from, pgoff_t idx_to) >>> -{ >>> - struct rb_node *n; >>> - >>> - n = fi->writepages.rb_node; >>> - >>> - while (n) { >>> - struct fuse_writepage_args *wpa; >>> - pgoff_t curr_index; >>> - >> >> -- >> Thanks, >> Jingbo
On Wed, Apr 9, 2025 at 7:12 PM Jingbo Xu <jefflexu@linux.alibaba.com> wrote: > > > > On 4/10/25 7:47 AM, Joanne Koong wrote: > > On Tue, Apr 8, 2025 at 7:43 PM Jingbo Xu <jefflexu@linux.alibaba.com> wrote: > >> > >> Hi Joanne, > >> > >> On 4/5/25 2:14 AM, Joanne Koong wrote: > >>> In the current FUSE writeback design (see commit 3be5a52b30aa > >>> ("fuse: support writable mmap")), a temp page is allocated for every > >>> dirty page to be written back, the contents of the dirty page are copied over > >>> to the temp page, and the temp page gets handed to the server to write back. > >>> > >>> This is done so that writeback may be immediately cleared on the dirty page, > >>> and this in turn is done in order to mitigate the following deadlock scenario > >>> that may arise if reclaim waits on writeback on the dirty page to complete: > >>> * single-threaded FUSE server is in the middle of handling a request > >>> that needs a memory allocation > >>> * memory allocation triggers direct reclaim > >>> * direct reclaim waits on a folio under writeback > >>> * the FUSE server can't write back the folio since it's stuck in > >>> direct reclaim > >>> > >>> With a recent change that added AS_WRITEBACK_INDETERMINATE and mitigates > >>> the situations described above, FUSE writeback does not need to use > >>> temp pages if it sets AS_WRITEBACK_INDETERMINATE on its inode mappings. > >>> > >>> This commit sets AS_WRITEBACK_INDETERMINATE on the inode mappings > >>> and removes the temporary pages + extra copying and the internal rb > >>> tree. > >>> > >>> fio benchmarks -- > >>> (using averages observed from 10 runs, throwing away outliers) > >>> > >>> Setup: > >>> sudo mount -t tmpfs -o size=30G tmpfs ~/tmp_mount > >>> ./libfuse/build/example/passthrough_ll -o writeback -o max_threads=4 -o source=~/tmp_mount ~/fuse_mount > >>> > >>> fio --name=writeback --ioengine=sync --rw=write --bs={1k,4k,1M} --size=2G > >>> --numjobs=2 --ramp_time=30 --group_reporting=1 --directory=/root/fuse_mount > >>> > >>> bs = 1k 4k 1M > >>> Before 351 MiB/s 1818 MiB/s 1851 MiB/s > >>> After 341 MiB/s 2246 MiB/s 2685 MiB/s > >>> % diff -3% 23% 45% > >>> > >>> Signed-off-by: Joanne Koong <joannelkoong@gmail.com> > >>> Reviewed-by: Jingbo Xu <jefflexu@linux.alibaba.com> > >>> Acked-by: Miklos Szeredi <mszeredi@redhat.com> > >> > > > > Hi Jingbo, > > > > Thanks for sharing your analysis for this. > > > >> Overall this patch LGTM. > >> > >> Apart from that, IMO the fi->writectr and fi->queued_writes mechanism is > >> also unneeded then, at least the DIRECT IO routine (i.e. > > > > I took a look at fi->writectr and fi->queued_writes and my > > understanding is that we do still need this. For example, for > > truncates (I'm looking at fuse_do_setattr()), I think we still need to > > prevent concurrent writeback or else the setattr request and the > > writeback request could race which would result in a mismatch between > > the file's reported size and the actual data written to disk. > > I haven't looked into the truncate routine yet. I will see it later. > > > > >> fuse_direct_io()) doesn't need fuse_sync_writes() anymore. That is > >> because after removing the temp page, the DIRECT IO routine has already > >> been waiting for all inflight WRITE requests, see > >> > >> # DIRECT read > >> generic_file_read_iter > >> kiocb_write_and_wait > >> filemap_write_and_wait_range > > > > Where do you see generic_file_read_iter() getting called for direct io reads? > > # DIRECT read > fuse_file_read_iter > fuse_cache_read_iter > generic_file_read_iter > kiocb_write_and_wait > filemap_write_and_wait_range > a_ops->direct_IO(),i.e. fuse_direct_IO() > Oh I see, I thought files opened with O_DIRECT automatically call the .direct_IO handler for reads/writes but you're right, it first goes through .read_iter / .write_iter handlers, and the .direct_IO handler only gets invoked through generic_file_read_iter() / generic_file_direct_write() in mm/filemap.c There's two paths for direct io in FUSE: a) fuse server sets fi->direct_io = true when a file is opened, which will set the FOPEN_DIRECT_IO bit in ff->open_flags on the kernel side b) fuse server doesn't set fi->direct_io = true, but the client opens the file with O_DIRECT We only go through the stack trace you listed above for the b) case. For the a) case, we'll hit if (ff->open_flags & FOPEN_DIRECT_IO) return fuse_direct_read_iter(iocb, to); and if (ff->open_flags & FOPEN_DIRECT_IO) return fuse_direct_write_iter(iocb, from); which will invoke fuse_direct_IO() / fuse_direct_io() without going through the kiocb_write_and_wait() -> filemap_write_and_wait_range() / kiocb_invalidate_pages() -> filemap_write_and_wait_range() you listed above. So for the a) case I think we'd still need the fuse_sync_writes() in case there's still pending writeback. Do you agree with this analysis or am I missing something here? > > > Similarly, where do you see generic_file_write_iter() getting called > > for direct io writes? > > # DIRECT read > fuse_file_write_iter > fuse_cache_write_iter > generic_file_write_iter > generic_file_direct_write > kiocb_invalidate_pages > filemap_invalidate_pages > filemap_write_and_wait_range > a_ops->direct_IO(),i.e. fuse_direct_IO() > > > > Where do you see fi->writectr / fi->queued-writes preventing this > > race? > > IMO overall fi->writectr / fi->queued-writes are introduced to prevent > DIRECT IO and writeback from sending duplicate (inflight) WRITE requests > for the same page. > > For the DIRECT write routine: > > # non-FOPEN_DIRECT_IO DIRECT write > fuse_cache_write_iter > fuse_direct_IO > fuse_direct_io > fuse_sync_writes > > > # FOPEN_DIRECT_IO DIRECT write > fuse_direct_write_iter > fuse_direct_IO > fuse_direct_io > fuse_sync_writes > > > For the writeback routine: > fuse_writepages() > fuse_writepages_fill > fuse_writepages_send > # buffer the WRITE request in queued_writes list > fuse_flush_writepages > # flush WRITE only when fi->writectr >= 0 > > > > > It looks to me like in the existing code, this race condition > > you described of direct write invalidating the page cache, then > > another buffer write reads the page cache and dirties it, then > > writeback is called on that, and the 2 write requests racing, could > > still happen? > > > > > >> However it seems that the writeback > >> won't wait for previous inflight DIRECT WRITE requests, so I'm not much > >> sure about that. Maybe other folks could offer more insights... > > > > My understanding is that these lines > > > > if (!cuse && filemap_range_has_writeback(...)) { > > ... > > fuse_sync_writes(inode); > > ... > > } > > > > in fuse_direct_io() is what waits on previous inflight direct write > > requests to complete before the direct io happens. > > Right. > > > > > > >> > >> Also fuse_sync_writes() is not needed in fuse_flush() anymore, with > >> which I'm pretty sure. > > > > Why don't we still need this for fuse_flush()? > > > > If a caller calls close(), this will call > > > > filp_close() > > filp_flush() > > filp->f_op->flush() > > fuse_flush() > > > > it seems like we should still be waiting for all writebacks to finish > > before sending the fuse server the fuse_flush request, no? > > > > filp_close() > filp_flush() > filp->f_op->flush() > fuse_flush() > write_inode_now > writeback_single_inode(WB_SYNC_ALL) > do_writepages > # flush dirty page > filemap_fdatawait > # wait for WRITE completion Nice. I missed that write_inode_now() will invoke filemap_fdatawait(). This seems pretty straightforward. I'll remove the fuse_sync_writes() call in fuse_flush() when I send out v8. The direct io one above is less straight-forward. I won't add that to v8 but that can be done in a separate future patch when we figure that out. Thanks, Joanne > > >> > >>> --- > >>> fs/fuse/file.c | 360 ++++------------------------------------------- > >>> fs/fuse/fuse_i.h | 3 - > >>> 2 files changed, 28 insertions(+), 335 deletions(-) > >>> > >>> diff --git a/fs/fuse/file.c b/fs/fuse/file.c > >>> index 754378dd9f71..91ada0208863 100644 > >>> --- a/fs/fuse/file.c > >>> +++ b/fs/fuse/file.c > >>> @@ -415,89 +415,11 @@ u64 fuse_lock_owner_id(struct fuse_conn *fc, fl_owner_t id) > >>> > >>> struct fuse_writepage_args { > >>> struct fuse_io_args ia; > >>> - struct rb_node writepages_entry; > >>> struct list_head queue_entry; > >>> - struct fuse_writepage_args *next; > >>> struct inode *inode; > >>> struct fuse_sync_bucket *bucket; > >>> }; > >>> > >>> -static struct fuse_writepage_args *fuse_find_writeback(struct fuse_inode *fi, > >>> - pgoff_t idx_from, pgoff_t idx_to) > >>> -{ > >>> - struct rb_node *n; > >>> - > >>> - n = fi->writepages.rb_node; > >>> - > >>> - while (n) { > >>> - struct fuse_writepage_args *wpa; > >>> - pgoff_t curr_index; > >>> - > >> > >> -- > >> Thanks, > >> Jingbo > > -- > Thanks, > Jingbo
On 4/10/25 11:07 PM, Joanne Koong wrote: > On Wed, Apr 9, 2025 at 7:12 PM Jingbo Xu <jefflexu@linux.alibaba.com> wrote: >> >> >> >> On 4/10/25 7:47 AM, Joanne Koong wrote: >>> On Tue, Apr 8, 2025 at 7:43 PM Jingbo Xu <jefflexu@linux.alibaba.com> wrote: >>>> >>>> Hi Joanne, >>>> >>>> On 4/5/25 2:14 AM, Joanne Koong wrote: >>>>> In the current FUSE writeback design (see commit 3be5a52b30aa >>>>> ("fuse: support writable mmap")), a temp page is allocated for every >>>>> dirty page to be written back, the contents of the dirty page are copied over >>>>> to the temp page, and the temp page gets handed to the server to write back. >>>>> >>>>> This is done so that writeback may be immediately cleared on the dirty page, >>>>> and this in turn is done in order to mitigate the following deadlock scenario >>>>> that may arise if reclaim waits on writeback on the dirty page to complete: >>>>> * single-threaded FUSE server is in the middle of handling a request >>>>> that needs a memory allocation >>>>> * memory allocation triggers direct reclaim >>>>> * direct reclaim waits on a folio under writeback >>>>> * the FUSE server can't write back the folio since it's stuck in >>>>> direct reclaim >>>>> >>>>> With a recent change that added AS_WRITEBACK_INDETERMINATE and mitigates >>>>> the situations described above, FUSE writeback does not need to use >>>>> temp pages if it sets AS_WRITEBACK_INDETERMINATE on its inode mappings. >>>>> >>>>> This commit sets AS_WRITEBACK_INDETERMINATE on the inode mappings >>>>> and removes the temporary pages + extra copying and the internal rb >>>>> tree. >>>>> >>>>> fio benchmarks -- >>>>> (using averages observed from 10 runs, throwing away outliers) >>>>> >>>>> Setup: >>>>> sudo mount -t tmpfs -o size=30G tmpfs ~/tmp_mount >>>>> ./libfuse/build/example/passthrough_ll -o writeback -o max_threads=4 -o source=~/tmp_mount ~/fuse_mount >>>>> >>>>> fio --name=writeback --ioengine=sync --rw=write --bs={1k,4k,1M} --size=2G >>>>> --numjobs=2 --ramp_time=30 --group_reporting=1 --directory=/root/fuse_mount >>>>> >>>>> bs = 1k 4k 1M >>>>> Before 351 MiB/s 1818 MiB/s 1851 MiB/s >>>>> After 341 MiB/s 2246 MiB/s 2685 MiB/s >>>>> % diff -3% 23% 45% >>>>> >>>>> Signed-off-by: Joanne Koong <joannelkoong@gmail.com> >>>>> Reviewed-by: Jingbo Xu <jefflexu@linux.alibaba.com> >>>>> Acked-by: Miklos Szeredi <mszeredi@redhat.com> >>>> >>> >>> Hi Jingbo, >>> >>> Thanks for sharing your analysis for this. >>> >>>> Overall this patch LGTM. >>>> >>>> Apart from that, IMO the fi->writectr and fi->queued_writes mechanism is >>>> also unneeded then, at least the DIRECT IO routine (i.e. >>> >>> I took a look at fi->writectr and fi->queued_writes and my >>> understanding is that we do still need this. For example, for >>> truncates (I'm looking at fuse_do_setattr()), I think we still need to >>> prevent concurrent writeback or else the setattr request and the >>> writeback request could race which would result in a mismatch between >>> the file's reported size and the actual data written to disk. >> >> I haven't looked into the truncate routine yet. I will see it later. >> >>> >>>> fuse_direct_io()) doesn't need fuse_sync_writes() anymore. That is >>>> because after removing the temp page, the DIRECT IO routine has already >>>> been waiting for all inflight WRITE requests, see >>>> >>>> # DIRECT read >>>> generic_file_read_iter >>>> kiocb_write_and_wait >>>> filemap_write_and_wait_range >>> >>> Where do you see generic_file_read_iter() getting called for direct io reads? >> >> # DIRECT read >> fuse_file_read_iter >> fuse_cache_read_iter >> generic_file_read_iter >> kiocb_write_and_wait >> filemap_write_and_wait_range >> a_ops->direct_IO(),i.e. fuse_direct_IO() >> > > Oh I see, I thought files opened with O_DIRECT automatically call the > .direct_IO handler for reads/writes but you're right, it first goes > through .read_iter / .write_iter handlers, and the .direct_IO handler > only gets invoked through generic_file_read_iter() / > generic_file_direct_write() in mm/filemap.c > > There's two paths for direct io in FUSE: > a) fuse server sets fi->direct_io = true when a file is opened, which > will set the FOPEN_DIRECT_IO bit in ff->open_flags on the kernel side > b) fuse server doesn't set fi->direct_io = true, but the client opens > the file with O_DIRECT > > We only go through the stack trace you listed above for the b) case. > For the a) case, we'll hit > > if (ff->open_flags & FOPEN_DIRECT_IO) > return fuse_direct_read_iter(iocb, to); > > and > > if (ff->open_flags & FOPEN_DIRECT_IO) > return fuse_direct_write_iter(iocb, from); > > which will invoke fuse_direct_IO() / fuse_direct_io() without going > through the kiocb_write_and_wait() -> filemap_write_and_wait_range() / > kiocb_invalidate_pages() -> filemap_write_and_wait_range() you listed > above. > > So for the a) case I think we'd still need the fuse_sync_writes() in > case there's still pending writeback. > > Do you agree with this analysis or am I missing something here? Yeah, that's true. But instead of calling fuse_sync_writes(), we can call filemap_wait_range() or something similar here. >> filp_close() >> filp_flush() >> filp->f_op->flush() >> fuse_flush() >> write_inode_now >> writeback_single_inode(WB_SYNC_ALL) >> do_writepages >> # flush dirty page >> filemap_fdatawait >> # wait for WRITE completion > > Nice. I missed that write_inode_now() will invoke filemap_fdatawait(). > This seems pretty straightforward. I'll remove the fuse_sync_writes() > call in fuse_flush() when I send out v8. > > The direct io one above is less straight-forward. I won't add that to > v8 but that can be done in a separate future patch when we figure that > out. Thanks for keep working on this. Appreciated.
On Thu, Apr 10, 2025 at 8:11 AM Jingbo Xu <jefflexu@linux.alibaba.com> wrote: > > On 4/10/25 11:07 PM, Joanne Koong wrote: > > On Wed, Apr 9, 2025 at 7:12 PM Jingbo Xu <jefflexu@linux.alibaba.com> wrote: > >> > >> > >> > >> On 4/10/25 7:47 AM, Joanne Koong wrote: > >>> On Tue, Apr 8, 2025 at 7:43 PM Jingbo Xu <jefflexu@linux.alibaba.com> wrote: > >>>> > >>>> Hi Joanne, > >>>> > >>>> On 4/5/25 2:14 AM, Joanne Koong wrote: > >>>>> In the current FUSE writeback design (see commit 3be5a52b30aa > >>>>> ("fuse: support writable mmap")), a temp page is allocated for every > >>>>> dirty page to be written back, the contents of the dirty page are copied over > >>>>> to the temp page, and the temp page gets handed to the server to write back. > >>>>> > >>>>> This is done so that writeback may be immediately cleared on the dirty page, > >>>>> and this in turn is done in order to mitigate the following deadlock scenario > >>>>> that may arise if reclaim waits on writeback on the dirty page to complete: > >>>>> * single-threaded FUSE server is in the middle of handling a request > >>>>> that needs a memory allocation > >>>>> * memory allocation triggers direct reclaim > >>>>> * direct reclaim waits on a folio under writeback > >>>>> * the FUSE server can't write back the folio since it's stuck in > >>>>> direct reclaim > >>>>> > >>>>> With a recent change that added AS_WRITEBACK_INDETERMINATE and mitigates > >>>>> the situations described above, FUSE writeback does not need to use > >>>>> temp pages if it sets AS_WRITEBACK_INDETERMINATE on its inode mappings. > >>>>> > >>>>> This commit sets AS_WRITEBACK_INDETERMINATE on the inode mappings > >>>>> and removes the temporary pages + extra copying and the internal rb > >>>>> tree. > >>>>> > >>>>> fio benchmarks -- > >>>>> (using averages observed from 10 runs, throwing away outliers) > >>>>> > >>>>> Setup: > >>>>> sudo mount -t tmpfs -o size=30G tmpfs ~/tmp_mount > >>>>> ./libfuse/build/example/passthrough_ll -o writeback -o max_threads=4 -o source=~/tmp_mount ~/fuse_mount > >>>>> > >>>>> fio --name=writeback --ioengine=sync --rw=write --bs={1k,4k,1M} --size=2G > >>>>> --numjobs=2 --ramp_time=30 --group_reporting=1 --directory=/root/fuse_mount > >>>>> > >>>>> bs = 1k 4k 1M > >>>>> Before 351 MiB/s 1818 MiB/s 1851 MiB/s > >>>>> After 341 MiB/s 2246 MiB/s 2685 MiB/s > >>>>> % diff -3% 23% 45% > >>>>> > >>>>> Signed-off-by: Joanne Koong <joannelkoong@gmail.com> > >>>>> Reviewed-by: Jingbo Xu <jefflexu@linux.alibaba.com> > >>>>> Acked-by: Miklos Szeredi <mszeredi@redhat.com> > >>>> > >>> > >>> Hi Jingbo, > >>> > >>> Thanks for sharing your analysis for this. > >>> > >>>> Overall this patch LGTM. > >>>> > >>>> Apart from that, IMO the fi->writectr and fi->queued_writes mechanism is > >>>> also unneeded then, at least the DIRECT IO routine (i.e. > >>> > >>> I took a look at fi->writectr and fi->queued_writes and my > >>> understanding is that we do still need this. For example, for > >>> truncates (I'm looking at fuse_do_setattr()), I think we still need to > >>> prevent concurrent writeback or else the setattr request and the > >>> writeback request could race which would result in a mismatch between > >>> the file's reported size and the actual data written to disk. > >> > >> I haven't looked into the truncate routine yet. I will see it later. > >> > >>> > >>>> fuse_direct_io()) doesn't need fuse_sync_writes() anymore. That is > >>>> because after removing the temp page, the DIRECT IO routine has already > >>>> been waiting for all inflight WRITE requests, see > >>>> > >>>> # DIRECT read > >>>> generic_file_read_iter > >>>> kiocb_write_and_wait > >>>> filemap_write_and_wait_range > >>> > >>> Where do you see generic_file_read_iter() getting called for direct io reads? > >> > >> # DIRECT read > >> fuse_file_read_iter > >> fuse_cache_read_iter > >> generic_file_read_iter > >> kiocb_write_and_wait > >> filemap_write_and_wait_range > >> a_ops->direct_IO(),i.e. fuse_direct_IO() > >> > > > > Oh I see, I thought files opened with O_DIRECT automatically call the > > .direct_IO handler for reads/writes but you're right, it first goes > > through .read_iter / .write_iter handlers, and the .direct_IO handler > > only gets invoked through generic_file_read_iter() / > > generic_file_direct_write() in mm/filemap.c > > > > There's two paths for direct io in FUSE: > > a) fuse server sets fi->direct_io = true when a file is opened, which > > will set the FOPEN_DIRECT_IO bit in ff->open_flags on the kernel side > > b) fuse server doesn't set fi->direct_io = true, but the client opens > > the file with O_DIRECT > > > > We only go through the stack trace you listed above for the b) case. > > For the a) case, we'll hit > > > > if (ff->open_flags & FOPEN_DIRECT_IO) > > return fuse_direct_read_iter(iocb, to); > > > > and > > > > if (ff->open_flags & FOPEN_DIRECT_IO) > > return fuse_direct_write_iter(iocb, from); > > > > which will invoke fuse_direct_IO() / fuse_direct_io() without going > > through the kiocb_write_and_wait() -> filemap_write_and_wait_range() / > > kiocb_invalidate_pages() -> filemap_write_and_wait_range() you listed > > above. > > > > So for the a) case I think we'd still need the fuse_sync_writes() in > > case there's still pending writeback. > > > > Do you agree with this analysis or am I missing something here? > > Yeah, that's true. But instead of calling fuse_sync_writes(), we can > call filemap_wait_range() or something similar here. > Agreed. Actually, the more I look at this, the more I think we can replace all fuse_sync_writes() and get rid of it entirely. Right now, fuse_sync_writes() is called in: fuse_fsync(): /* * Start writeback against all dirty pages of the inode, then * wait for all outstanding writes, before sending the FSYNC * request. */ err = file_write_and_wait_range(file, start, end); if (err) goto out; fuse_sync_writes(inode); /* * Due to implementation of fuse writeback * file_write_and_wait_range() does not catch errors. * We have to do this directly after fuse_sync_writes() */ err = file_check_and_advance_wb_err(file); if (err) goto out; We can get rid of the fuse_sync_writes() and file_check_and_advance_wb_err() entirely since now without temp pages, the file_write_and_wait_range() call actually ensures that writeback is completed fuse_writeback_range(): static int fuse_writeback_range(struct inode *inode, loff_t start, loff_t end) { int err = filemap_write_and_wait_range(inode->i_mapping, start, LLONG_MAX); if (!err) fuse_sync_writes(inode); return err; } We can replace fuse_writeback_range() entirely with filemap_write_and_wait_range(). fuse_direct_io(): if (fopen_direct_io && fc->direct_io_allow_mmap) { res = filemap_write_and_wait_range(mapping, pos, pos + count - 1); if (res) { fuse_io_free(ia); return res; } } if (!cuse && filemap_range_has_writeback(mapping, pos, (pos + count - 1))) { if (!write) inode_lock(inode); fuse_sync_writes(inode); if (!write) inode_unlock(inode); } I think this can just replaced with if (fopen_direct_io && (fc->direct_io_allow_mmap || !cuse)) { res = filemap_write_and_wait_range(mapping, pos, pos + count - 1); if (res) { fuse_io_free(ia); return res; } } since for the !fopen_direct_io case, it will already go through filemap_write_and_wait_range(), as you mentioned in your previous message. I think this also fixes a bug (?) in the original code - in the fopen_direct_io && !fc->direct_io_allow_mmap case, I think we still need to write out dirty pages first, which we don't currently do. What do you think? Thanks for all your careful review on this patchset throughout all of its iterations. > > > >> filp_close() > >> filp_flush() > >> filp->f_op->flush() > >> fuse_flush() > >> write_inode_now > >> writeback_single_inode(WB_SYNC_ALL) > >> do_writepages > >> # flush dirty page > >> filemap_fdatawait > >> # wait for WRITE completion > > > > Nice. I missed that write_inode_now() will invoke filemap_fdatawait(). > > This seems pretty straightforward. I'll remove the fuse_sync_writes() > > call in fuse_flush() when I send out v8. > > > > The direct io one above is less straight-forward. I won't add that to > > v8 but that can be done in a separate future patch when we figure that > > out. > > Thanks for keep working on this. Appreciated. > > -- > Thanks, > Jingbo
diff --git a/fs/fuse/file.c b/fs/fuse/file.c index 754378dd9f71..91ada0208863 100644 --- a/fs/fuse/file.c +++ b/fs/fuse/file.c @@ -415,89 +415,11 @@ u64 fuse_lock_owner_id(struct fuse_conn *fc, fl_owner_t id) struct fuse_writepage_args { struct fuse_io_args ia; - struct rb_node writepages_entry; struct list_head queue_entry; - struct fuse_writepage_args *next; struct inode *inode; struct fuse_sync_bucket *bucket; }; -static struct fuse_writepage_args *fuse_find_writeback(struct fuse_inode *fi, - pgoff_t idx_from, pgoff_t idx_to) -{ - struct rb_node *n; - - n = fi->writepages.rb_node; - - while (n) { - struct fuse_writepage_args *wpa; - pgoff_t curr_index; - - wpa = rb_entry(n, struct fuse_writepage_args, writepages_entry); - WARN_ON(get_fuse_inode(wpa->inode) != fi); - curr_index = wpa->ia.write.in.offset >> PAGE_SHIFT; - if (idx_from >= curr_index + wpa->ia.ap.num_folios) - n = n->rb_right; - else if (idx_to < curr_index) - n = n->rb_left; - else - return wpa; - } - return NULL; -} - -/* - * Check if any page in a range is under writeback - */ -static bool fuse_range_is_writeback(struct inode *inode, pgoff_t idx_from, - pgoff_t idx_to) -{ - struct fuse_inode *fi = get_fuse_inode(inode); - bool found; - - if (RB_EMPTY_ROOT(&fi->writepages)) - return false; - - spin_lock(&fi->lock); - found = fuse_find_writeback(fi, idx_from, idx_to); - spin_unlock(&fi->lock); - - return found; -} - -static inline bool fuse_page_is_writeback(struct inode *inode, pgoff_t index) -{ - return fuse_range_is_writeback(inode, index, index); -} - -/* - * Wait for page writeback to be completed. - * - * Since fuse doesn't rely on the VM writeback tracking, this has to - * use some other means. - */ -static void fuse_wait_on_page_writeback(struct inode *inode, pgoff_t index) -{ - struct fuse_inode *fi = get_fuse_inode(inode); - - wait_event(fi->page_waitq, !fuse_page_is_writeback(inode, index)); -} - -static inline bool fuse_folio_is_writeback(struct inode *inode, - struct folio *folio) -{ - pgoff_t last = folio_next_index(folio) - 1; - return fuse_range_is_writeback(inode, folio_index(folio), last); -} - -static void fuse_wait_on_folio_writeback(struct inode *inode, - struct folio *folio) -{ - struct fuse_inode *fi = get_fuse_inode(inode); - - wait_event(fi->page_waitq, !fuse_folio_is_writeback(inode, folio)); -} - /* * Wait for all pending writepages on the inode to finish. * @@ -886,13 +808,6 @@ static int fuse_do_readfolio(struct file *file, struct folio *folio) ssize_t res; u64 attr_ver; - /* - * With the temporary pages that are used to complete writeback, we can - * have writeback that extends beyond the lifetime of the folio. So - * make sure we read a properly synced folio. - */ - fuse_wait_on_folio_writeback(inode, folio); - attr_ver = fuse_get_attr_version(fm->fc); /* Don't overflow end offset */ @@ -1005,17 +920,12 @@ static void fuse_send_readpages(struct fuse_io_args *ia, struct file *file) static void fuse_readahead(struct readahead_control *rac) { struct inode *inode = rac->mapping->host; - struct fuse_inode *fi = get_fuse_inode(inode); struct fuse_conn *fc = get_fuse_conn(inode); unsigned int max_pages, nr_pages; - pgoff_t first = readahead_index(rac); - pgoff_t last = first + readahead_count(rac) - 1; if (fuse_is_bad(inode)) return; - wait_event(fi->page_waitq, !fuse_range_is_writeback(inode, first, last)); - max_pages = min_t(unsigned int, fc->max_pages, fc->max_read / PAGE_SIZE); @@ -1181,7 +1091,7 @@ static ssize_t fuse_send_write_pages(struct fuse_io_args *ia, int err; for (i = 0; i < ap->num_folios; i++) - fuse_wait_on_folio_writeback(inode, ap->folios[i]); + folio_wait_writeback(ap->folios[i]); fuse_write_args_fill(ia, ff, pos, count); ia->write.in.flags = fuse_write_flags(iocb); @@ -1638,7 +1548,7 @@ ssize_t fuse_direct_io(struct fuse_io_priv *io, struct iov_iter *iter, return res; } } - if (!cuse && fuse_range_is_writeback(inode, idx_from, idx_to)) { + if (!cuse && filemap_range_has_writeback(mapping, pos, (pos + count - 1))) { if (!write) inode_lock(inode); fuse_sync_writes(inode); @@ -1835,38 +1745,34 @@ static ssize_t fuse_splice_write(struct pipe_inode_info *pipe, struct file *out, static void fuse_writepage_free(struct fuse_writepage_args *wpa) { struct fuse_args_pages *ap = &wpa->ia.ap; - int i; if (wpa->bucket) fuse_sync_bucket_dec(wpa->bucket); - for (i = 0; i < ap->num_folios; i++) - folio_put(ap->folios[i]); - fuse_file_put(wpa->ia.ff, false); kfree(ap->folios); kfree(wpa); } -static void fuse_writepage_finish_stat(struct inode *inode, struct folio *folio) -{ - struct backing_dev_info *bdi = inode_to_bdi(inode); - - dec_wb_stat(&bdi->wb, WB_WRITEBACK); - node_stat_sub_folio(folio, NR_WRITEBACK_TEMP); - wb_writeout_inc(&bdi->wb); -} - static void fuse_writepage_finish(struct fuse_writepage_args *wpa) { struct fuse_args_pages *ap = &wpa->ia.ap; struct inode *inode = wpa->inode; struct fuse_inode *fi = get_fuse_inode(inode); + struct backing_dev_info *bdi = inode_to_bdi(inode); int i; - for (i = 0; i < ap->num_folios; i++) - fuse_writepage_finish_stat(inode, ap->folios[i]); + for (i = 0; i < ap->num_folios; i++) { + /* + * Benchmarks showed that ending writeback within the + * scope of the fi->lock alleviates xarray lock + * contention and noticeably improves performance. + */ + folio_end_writeback(ap->folios[i]); + dec_wb_stat(&bdi->wb, WB_WRITEBACK); + wb_writeout_inc(&bdi->wb); + } wake_up(&fi->page_waitq); } @@ -1877,7 +1783,6 @@ static void fuse_send_writepage(struct fuse_mount *fm, __releases(fi->lock) __acquires(fi->lock) { - struct fuse_writepage_args *aux, *next; struct fuse_inode *fi = get_fuse_inode(wpa->inode); struct fuse_write_in *inarg = &wpa->ia.write.in; struct fuse_args *args = &wpa->ia.ap.args; @@ -1914,19 +1819,8 @@ __acquires(fi->lock) out_free: fi->writectr--; - rb_erase(&wpa->writepages_entry, &fi->writepages); fuse_writepage_finish(wpa); spin_unlock(&fi->lock); - - /* After rb_erase() aux request list is private */ - for (aux = wpa->next; aux; aux = next) { - next = aux->next; - aux->next = NULL; - fuse_writepage_finish_stat(aux->inode, - aux->ia.ap.folios[0]); - fuse_writepage_free(aux); - } - fuse_writepage_free(wpa); spin_lock(&fi->lock); } @@ -1954,43 +1848,6 @@ __acquires(fi->lock) } } -static struct fuse_writepage_args *fuse_insert_writeback(struct rb_root *root, - struct fuse_writepage_args *wpa) -{ - pgoff_t idx_from = wpa->ia.write.in.offset >> PAGE_SHIFT; - pgoff_t idx_to = idx_from + wpa->ia.ap.num_folios - 1; - struct rb_node **p = &root->rb_node; - struct rb_node *parent = NULL; - - WARN_ON(!wpa->ia.ap.num_folios); - while (*p) { - struct fuse_writepage_args *curr; - pgoff_t curr_index; - - parent = *p; - curr = rb_entry(parent, struct fuse_writepage_args, - writepages_entry); - WARN_ON(curr->inode != wpa->inode); - curr_index = curr->ia.write.in.offset >> PAGE_SHIFT; - - if (idx_from >= curr_index + curr->ia.ap.num_folios) - p = &(*p)->rb_right; - else if (idx_to < curr_index) - p = &(*p)->rb_left; - else - return curr; - } - - rb_link_node(&wpa->writepages_entry, parent, p); - rb_insert_color(&wpa->writepages_entry, root); - return NULL; -} - -static void tree_insert(struct rb_root *root, struct fuse_writepage_args *wpa) -{ - WARN_ON(fuse_insert_writeback(root, wpa)); -} - static void fuse_writepage_end(struct fuse_mount *fm, struct fuse_args *args, int error) { @@ -2010,41 +1867,6 @@ static void fuse_writepage_end(struct fuse_mount *fm, struct fuse_args *args, if (!fc->writeback_cache) fuse_invalidate_attr_mask(inode, FUSE_STATX_MODIFY); spin_lock(&fi->lock); - rb_erase(&wpa->writepages_entry, &fi->writepages); - while (wpa->next) { - struct fuse_mount *fm = get_fuse_mount(inode); - struct fuse_write_in *inarg = &wpa->ia.write.in; - struct fuse_writepage_args *next = wpa->next; - - wpa->next = next->next; - next->next = NULL; - tree_insert(&fi->writepages, next); - - /* - * Skip fuse_flush_writepages() to make it easy to crop requests - * based on primary request size. - * - * 1st case (trivial): there are no concurrent activities using - * fuse_set/release_nowrite. Then we're on safe side because - * fuse_flush_writepages() would call fuse_send_writepage() - * anyway. - * - * 2nd case: someone called fuse_set_nowrite and it is waiting - * now for completion of all in-flight requests. This happens - * rarely and no more than once per page, so this should be - * okay. - * - * 3rd case: someone (e.g. fuse_do_setattr()) is in the middle - * of fuse_set_nowrite..fuse_release_nowrite section. The fact - * that fuse_set_nowrite returned implies that all in-flight - * requests were completed along with all of their secondary - * requests. Further primary requests are blocked by negative - * writectr. Hence there cannot be any in-flight requests and - * no invocations of fuse_writepage_end() while we're in - * fuse_set_nowrite..fuse_release_nowrite section. - */ - fuse_send_writepage(fm, next, inarg->offset + inarg->size); - } fi->writectr--; fuse_writepage_finish(wpa); spin_unlock(&fi->lock); @@ -2131,19 +1953,16 @@ static void fuse_writepage_add_to_bucket(struct fuse_conn *fc, } static void fuse_writepage_args_page_fill(struct fuse_writepage_args *wpa, struct folio *folio, - struct folio *tmp_folio, uint32_t folio_index) + uint32_t folio_index) { struct inode *inode = folio->mapping->host; struct fuse_args_pages *ap = &wpa->ia.ap; - folio_copy(tmp_folio, folio); - - ap->folios[folio_index] = tmp_folio; + ap->folios[folio_index] = folio; ap->descs[folio_index].offset = 0; ap->descs[folio_index].length = PAGE_SIZE; inc_wb_stat(&inode_to_bdi(inode)->wb, WB_WRITEBACK); - node_stat_add_folio(tmp_folio, NR_WRITEBACK_TEMP); } static struct fuse_writepage_args *fuse_writepage_args_setup(struct folio *folio, @@ -2178,18 +1997,12 @@ static int fuse_writepage_locked(struct folio *folio) struct fuse_inode *fi = get_fuse_inode(inode); struct fuse_writepage_args *wpa; struct fuse_args_pages *ap; - struct folio *tmp_folio; struct fuse_file *ff; - int error = -ENOMEM; - - tmp_folio = folio_alloc(GFP_NOFS | __GFP_HIGHMEM, 0); - if (!tmp_folio) - goto err; + int error = -EIO; - error = -EIO; ff = fuse_write_file_get(fi); if (!ff) - goto err_nofile; + goto err; wpa = fuse_writepage_args_setup(folio, ff); error = -ENOMEM; @@ -2200,22 +2013,17 @@ static int fuse_writepage_locked(struct folio *folio) ap->num_folios = 1; folio_start_writeback(folio); - fuse_writepage_args_page_fill(wpa, folio, tmp_folio, 0); + fuse_writepage_args_page_fill(wpa, folio, 0); spin_lock(&fi->lock); - tree_insert(&fi->writepages, wpa); list_add_tail(&wpa->queue_entry, &fi->queued_writes); fuse_flush_writepages(inode); spin_unlock(&fi->lock); - folio_end_writeback(folio); - return 0; err_writepage_args: fuse_file_put(ff, false); -err_nofile: - folio_put(tmp_folio); err: mapping_set_error(folio->mapping, error); return error; @@ -2225,7 +2033,6 @@ struct fuse_fill_wb_data { struct fuse_writepage_args *wpa; struct fuse_file *ff; struct inode *inode; - struct folio **orig_folios; unsigned int max_folios; }; @@ -2260,69 +2067,11 @@ static void fuse_writepages_send(struct fuse_fill_wb_data *data) struct fuse_writepage_args *wpa = data->wpa; struct inode *inode = data->inode; struct fuse_inode *fi = get_fuse_inode(inode); - int num_folios = wpa->ia.ap.num_folios; - int i; spin_lock(&fi->lock); list_add_tail(&wpa->queue_entry, &fi->queued_writes); fuse_flush_writepages(inode); spin_unlock(&fi->lock); - - for (i = 0; i < num_folios; i++) - folio_end_writeback(data->orig_folios[i]); -} - -/* - * Check under fi->lock if the page is under writeback, and insert it onto the - * rb_tree if not. Otherwise iterate auxiliary write requests, to see if there's - * one already added for a page at this offset. If there's none, then insert - * this new request onto the auxiliary list, otherwise reuse the existing one by - * swapping the new temp page with the old one. - */ -static bool fuse_writepage_add(struct fuse_writepage_args *new_wpa, - struct folio *folio) -{ - struct fuse_inode *fi = get_fuse_inode(new_wpa->inode); - struct fuse_writepage_args *tmp; - struct fuse_writepage_args *old_wpa; - struct fuse_args_pages *new_ap = &new_wpa->ia.ap; - - WARN_ON(new_ap->num_folios != 0); - new_ap->num_folios = 1; - - spin_lock(&fi->lock); - old_wpa = fuse_insert_writeback(&fi->writepages, new_wpa); - if (!old_wpa) { - spin_unlock(&fi->lock); - return true; - } - - for (tmp = old_wpa->next; tmp; tmp = tmp->next) { - pgoff_t curr_index; - - WARN_ON(tmp->inode != new_wpa->inode); - curr_index = tmp->ia.write.in.offset >> PAGE_SHIFT; - if (curr_index == folio->index) { - WARN_ON(tmp->ia.ap.num_folios != 1); - swap(tmp->ia.ap.folios[0], new_ap->folios[0]); - break; - } - } - - if (!tmp) { - new_wpa->next = old_wpa->next; - old_wpa->next = new_wpa; - } - - spin_unlock(&fi->lock); - - if (tmp) { - fuse_writepage_finish_stat(new_wpa->inode, - folio); - fuse_writepage_free(new_wpa); - } - - return false; } static bool fuse_writepage_need_send(struct fuse_conn *fc, struct folio *folio, @@ -2331,15 +2080,6 @@ static bool fuse_writepage_need_send(struct fuse_conn *fc, struct folio *folio, { WARN_ON(!ap->num_folios); - /* - * Being under writeback is unlikely but possible. For example direct - * read to an mmaped fuse file will set the page dirty twice; once when - * the pages are faulted with get_user_pages(), and then after the read - * completed. - */ - if (fuse_folio_is_writeback(data->inode, folio)) - return true; - /* Reached max pages */ if (ap->num_folios == fc->max_pages) return true; @@ -2349,7 +2089,7 @@ static bool fuse_writepage_need_send(struct fuse_conn *fc, struct folio *folio, return true; /* Discontinuity */ - if (data->orig_folios[ap->num_folios - 1]->index + 1 != folio_index(folio)) + if (ap->folios[ap->num_folios - 1]->index + 1 != folio_index(folio)) return true; /* Need to grow the pages array? If so, did the expansion fail? */ @@ -2368,7 +2108,6 @@ static int fuse_writepages_fill(struct folio *folio, struct inode *inode = data->inode; struct fuse_inode *fi = get_fuse_inode(inode); struct fuse_conn *fc = get_fuse_conn(inode); - struct folio *tmp_folio; int err; if (!data->ff) { @@ -2383,54 +2122,23 @@ static int fuse_writepages_fill(struct folio *folio, data->wpa = NULL; } - err = -ENOMEM; - tmp_folio = folio_alloc(GFP_NOFS | __GFP_HIGHMEM, 0); - if (!tmp_folio) - goto out_unlock; - - /* - * The page must not be redirtied until the writeout is completed - * (i.e. userspace has sent a reply to the write request). Otherwise - * there could be more than one temporary page instance for each real - * page. - * - * This is ensured by holding the page lock in page_mkwrite() while - * checking fuse_page_is_writeback(). We already hold the page lock - * since clear_page_dirty_for_io() and keep it held until we add the - * request to the fi->writepages list and increment ap->num_folios. - * After this fuse_page_is_writeback() will indicate that the page is - * under writeback, so we can release the page lock. - */ if (data->wpa == NULL) { err = -ENOMEM; wpa = fuse_writepage_args_setup(folio, data->ff); - if (!wpa) { - folio_put(tmp_folio); + if (!wpa) goto out_unlock; - } fuse_file_get(wpa->ia.ff); data->max_folios = 1; ap = &wpa->ia.ap; } folio_start_writeback(folio); - fuse_writepage_args_page_fill(wpa, folio, tmp_folio, ap->num_folios); - data->orig_folios[ap->num_folios] = folio; + fuse_writepage_args_page_fill(wpa, folio, ap->num_folios); err = 0; - if (data->wpa) { - /* - * Protected by fi->lock against concurrent access by - * fuse_page_is_writeback(). - */ - spin_lock(&fi->lock); - ap->num_folios++; - spin_unlock(&fi->lock); - } else if (fuse_writepage_add(wpa, folio)) { + ap->num_folios++; + if (!data->wpa) data->wpa = wpa; - } else { - folio_end_writeback(folio); - } out_unlock: folio_unlock(folio); @@ -2457,13 +2165,6 @@ static int fuse_writepages(struct address_space *mapping, data.wpa = NULL; data.ff = NULL; - err = -ENOMEM; - data.orig_folios = kcalloc(fc->max_pages, - sizeof(struct folio *), - GFP_NOFS); - if (!data.orig_folios) - goto out; - err = write_cache_pages(mapping, wbc, fuse_writepages_fill, &data); if (data.wpa) { WARN_ON(!data.wpa->ia.ap.num_folios); @@ -2472,7 +2173,6 @@ static int fuse_writepages(struct address_space *mapping, if (data.ff) fuse_file_put(data.ff, false); - kfree(data.orig_folios); out: return err; } @@ -2497,8 +2197,6 @@ static int fuse_write_begin(struct file *file, struct address_space *mapping, if (IS_ERR(folio)) goto error; - fuse_wait_on_page_writeback(mapping->host, folio->index); - if (folio_test_uptodate(folio) || len >= folio_size(folio)) goto success; /* @@ -2561,13 +2259,9 @@ static int fuse_launder_folio(struct folio *folio) { int err = 0; if (folio_clear_dirty_for_io(folio)) { - struct inode *inode = folio->mapping->host; - - /* Serialize with pending writeback for the same page */ - fuse_wait_on_page_writeback(inode, folio->index); err = fuse_writepage_locked(folio); if (!err) - fuse_wait_on_page_writeback(inode, folio->index); + folio_wait_writeback(folio); } return err; } @@ -2611,7 +2305,7 @@ static vm_fault_t fuse_page_mkwrite(struct vm_fault *vmf) return VM_FAULT_NOPAGE; } - fuse_wait_on_folio_writeback(inode, folio); + folio_wait_writeback(folio); return VM_FAULT_LOCKED; } @@ -3429,9 +3123,12 @@ static const struct address_space_operations fuse_file_aops = { void fuse_init_file_inode(struct inode *inode, unsigned int flags) { struct fuse_inode *fi = get_fuse_inode(inode); + struct fuse_conn *fc = get_fuse_conn(inode); inode->i_fop = &fuse_file_operations; inode->i_data.a_ops = &fuse_file_aops; + if (fc->writeback_cache) + mapping_set_writeback_indeterminate(&inode->i_data); INIT_LIST_HEAD(&fi->write_files); INIT_LIST_HEAD(&fi->queued_writes); @@ -3439,7 +3136,6 @@ void fuse_init_file_inode(struct inode *inode, unsigned int flags) fi->iocachectr = 0; init_waitqueue_head(&fi->page_waitq); init_waitqueue_head(&fi->direct_io_waitq); - fi->writepages = RB_ROOT; if (IS_ENABLED(CONFIG_FUSE_DAX)) fuse_dax_inode_init(inode, flags); diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h index fee96fe7887b..28a101a5c558 100644 --- a/fs/fuse/fuse_i.h +++ b/fs/fuse/fuse_i.h @@ -141,9 +141,6 @@ struct fuse_inode { /* waitq for direct-io completion */ wait_queue_head_t direct_io_waitq; - - /* List of writepage requestst (pending or sent) */ - struct rb_root writepages; }; /* readdir cache (directory only) */
In the current FUSE writeback design (see commit 3be5a52b30aa ("fuse: support writable mmap")), a temp page is allocated for every dirty page to be written back, the contents of the dirty page are copied over to the temp page, and the temp page gets handed to the server to write back. This is done so that writeback may be immediately cleared on the dirty page, and this in turn is done in order to mitigate the following deadlock scenario that may arise if reclaim waits on writeback on the dirty page to complete: * single-threaded FUSE server is in the middle of handling a request that needs a memory allocation * memory allocation triggers direct reclaim * direct reclaim waits on a folio under writeback * the FUSE server can't write back the folio since it's stuck in direct reclaim With a recent change that added AS_WRITEBACK_INDETERMINATE and mitigates the situations described above, FUSE writeback does not need to use temp pages if it sets AS_WRITEBACK_INDETERMINATE on its inode mappings. This commit sets AS_WRITEBACK_INDETERMINATE on the inode mappings and removes the temporary pages + extra copying and the internal rb tree. fio benchmarks -- (using averages observed from 10 runs, throwing away outliers) Setup: sudo mount -t tmpfs -o size=30G tmpfs ~/tmp_mount ./libfuse/build/example/passthrough_ll -o writeback -o max_threads=4 -o source=~/tmp_mount ~/fuse_mount fio --name=writeback --ioengine=sync --rw=write --bs={1k,4k,1M} --size=2G --numjobs=2 --ramp_time=30 --group_reporting=1 --directory=/root/fuse_mount bs = 1k 4k 1M Before 351 MiB/s 1818 MiB/s 1851 MiB/s After 341 MiB/s 2246 MiB/s 2685 MiB/s % diff -3% 23% 45% Signed-off-by: Joanne Koong <joannelkoong@gmail.com> Reviewed-by: Jingbo Xu <jefflexu@linux.alibaba.com> Acked-by: Miklos Szeredi <mszeredi@redhat.com> --- fs/fuse/file.c | 360 ++++------------------------------------------- fs/fuse/fuse_i.h | 3 - 2 files changed, 28 insertions(+), 335 deletions(-)