| Message ID | 20200414150233.24495-25-willy@infradead.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Change readahead API | expand |
On Tue, Apr 14, 2020 at 5:08 PM Matthew Wilcox <willy@infradead.org> wrote: > > From: "Matthew Wilcox (Oracle)" <willy@infradead.org> > > Implement the new readahead operation in fuse by using __readahead_batch() > to fill the array of pages in fuse_args_pages directly. This lets us > inline fuse_readpages_fill() into fuse_readahead(). > > Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> > Reviewed-by: Dave Chinner <dchinner@redhat.com> > Reviewed-by: William Kucharski <william.kucharski@oracle.com> > --- > fs/fuse/file.c | 99 ++++++++++++++------------------------------------ > 1 file changed, 27 insertions(+), 72 deletions(-) > > diff --git a/fs/fuse/file.c b/fs/fuse/file.c > index 9d67b830fb7a..db82fb29dd39 100644 > --- a/fs/fuse/file.c > +++ b/fs/fuse/file.c > @@ -915,84 +915,39 @@ static void fuse_send_readpages(struct fuse_io_args *ia, struct file *file) > fuse_readpages_end(fc, &ap->args, err); > } > > -struct fuse_fill_data { > - struct fuse_io_args *ia; > - struct file *file; > - struct inode *inode; > - unsigned int nr_pages; > - unsigned int max_pages; > -}; > - > -static int fuse_readpages_fill(void *_data, struct page *page) > +static void fuse_readahead(struct readahead_control *rac) > { > - struct fuse_fill_data *data = _data; > - struct fuse_io_args *ia = data->ia; > - struct fuse_args_pages *ap = &ia->ap; > - struct inode *inode = data->inode; > + struct inode *inode = rac->mapping->host; > struct fuse_conn *fc = get_fuse_conn(inode); > + unsigned int i, max_pages, nr_pages = 0; > > - fuse_wait_on_page_writeback(inode, page->index); > - > - if (ap->num_pages && > - (ap->num_pages == fc->max_pages || > - (ap->num_pages + 1) * PAGE_SIZE > fc->max_read || > - ap->pages[ap->num_pages - 1]->index + 1 != page->index)) { > - data->max_pages = min_t(unsigned int, data->nr_pages, > - fc->max_pages); > - fuse_send_readpages(ia, data->file); > - data->ia = ia = fuse_io_alloc(NULL, data->max_pages); > - if (!ia) { > - unlock_page(page); > - return -ENOMEM; > - } > - ap = &ia->ap; > - } > - > - if (WARN_ON(ap->num_pages >= data->max_pages)) { > - unlock_page(page); > - fuse_io_free(ia); > - return -EIO; > - } > - > - get_page(page); > - ap->pages[ap->num_pages] = page; > - ap->descs[ap->num_pages].length = PAGE_SIZE; > - ap->num_pages++; > - data->nr_pages--; > - return 0; > -} > - > -static int fuse_readpages(struct file *file, struct address_space *mapping, > - struct list_head *pages, unsigned nr_pages) > -{ > - struct inode *inode = mapping->host; > - struct fuse_conn *fc = get_fuse_conn(inode); > - struct fuse_fill_data data; > - int err; > - > - err = -EIO; > if (is_bad_inode(inode)) > - goto out; > + return; > > - data.file = file; > - data.inode = inode; > - data.nr_pages = nr_pages; > - data.max_pages = min_t(unsigned int, nr_pages, fc->max_pages); > -; > - data.ia = fuse_io_alloc(NULL, data.max_pages); > - err = -ENOMEM; > - if (!data.ia) > - goto out; > + max_pages = min(fc->max_pages, fc->max_read / PAGE_SIZE); > > - err = read_cache_pages(mapping, pages, fuse_readpages_fill, &data); > - if (!err) { > - if (data.ia->ap.num_pages) > - fuse_send_readpages(data.ia, file); > - else > - fuse_io_free(data.ia); > + for (;;) { > + struct fuse_io_args *ia; > + struct fuse_args_pages *ap; > + > + nr_pages = readahead_count(rac) - nr_pages; Hmm. I see what's going on here, but it's confusing. Why is __readahead_batch() decrementing the readahead count at the start, rather than at the end? At the very least it needs a comment about why nr_pages is calculated this way. > + if (nr_pages > max_pages) > + nr_pages = max_pages; > + if (nr_pages == 0) > + break; > + ia = fuse_io_alloc(NULL, nr_pages); > + if (!ia) > + return; > + ap = &ia->ap; > + nr_pages = __readahead_batch(rac, ap->pages, nr_pages); > + for (i = 0; i < nr_pages; i++) { > + fuse_wait_on_page_writeback(inode, > + readahead_index(rac) + i); What's wrong with ap->pages[i]->index? Are we trying to wean off using ->index? Thanks, Miklos
On Mon, Apr 20, 2020 at 01:14:17PM +0200, Miklos Szeredi wrote: > > + for (;;) { > > + struct fuse_io_args *ia; > > + struct fuse_args_pages *ap; > > + > > + nr_pages = readahead_count(rac) - nr_pages; > > Hmm. I see what's going on here, but it's confusing. Why is > __readahead_batch() decrementing the readahead count at the start, > rather than at the end? > > At the very least it needs a comment about why nr_pages is calculated this way. Because usually that's what we want. See, for example, fs/mpage.c: while ((page = readahead_page(rac))) { prefetchw(&page->flags); args.page = page; args.nr_pages = readahead_count(rac); args.bio = do_mpage_readpage(&args); put_page(page); } fuse is different because it's trying to allocate for the next batch, not for the batch we're currently on. I'm a little annoyed because I posted almost this exact loop here: https://lore.kernel.org/linux-fsdevel/CAJfpegtrhGamoSqD-3Svfj3-iTdAbfD8TP44H_o+HE+g+CAnCA@mail.gmail.com/ and you said "I think that's fine", modified only by your concern for it not being obvious that nr_pages couldn't be decremented by __readahead_batch(), so I modified the loop slightly to assign to nr_pages. The part you're now complaining about is unchanged. > > + if (nr_pages > max_pages) > > + nr_pages = max_pages; > > + if (nr_pages == 0) > > + break; > > + ia = fuse_io_alloc(NULL, nr_pages); > > + if (!ia) > > + return; > > + ap = &ia->ap; > > + nr_pages = __readahead_batch(rac, ap->pages, nr_pages); > > + for (i = 0; i < nr_pages; i++) { > > + fuse_wait_on_page_writeback(inode, > > + readahead_index(rac) + i); > > What's wrong with ap->pages[i]->index? Are we trying to wean off using ->index? It saves reading from a cacheline? I wouldn't be surprised if the compiler hoisted the read from rac->_index to outside the loop and just iterated from rac->_index to rac->_index + nr_pages.
On Mon, Apr 20, 2020 at 1:43 PM Matthew Wilcox <willy@infradead.org> wrote: > > On Mon, Apr 20, 2020 at 01:14:17PM +0200, Miklos Szeredi wrote: > > > + for (;;) { > > > + struct fuse_io_args *ia; > > > + struct fuse_args_pages *ap; > > > + > > > + nr_pages = readahead_count(rac) - nr_pages; > > > > Hmm. I see what's going on here, but it's confusing. Why is > > __readahead_batch() decrementing the readahead count at the start, > > rather than at the end? > > > > At the very least it needs a comment about why nr_pages is calculated this way. > > Because usually that's what we want. See, for example, fs/mpage.c: > > while ((page = readahead_page(rac))) { > prefetchw(&page->flags); > args.page = page; > args.nr_pages = readahead_count(rac); > args.bio = do_mpage_readpage(&args); > put_page(page); > } > > fuse is different because it's trying to allocate for the next batch, > not for the batch we're currently on. > > I'm a little annoyed because I posted almost this exact loop here: > > https://lore.kernel.org/linux-fsdevel/CAJfpegtrhGamoSqD-3Svfj3-iTdAbfD8TP44H_o+HE+g+CAnCA@mail.gmail.com/ > > and you said "I think that's fine", modified only by your concern > for it not being obvious that nr_pages couldn't be decremented by > __readahead_batch(), so I modified the loop slightly to assign to > nr_pages. The part you're now complaining about is unchanged. Your annoyance is perfectly understandable. This is something I noticed now, not back then. > > > > + if (nr_pages > max_pages) > > > + nr_pages = max_pages; > > > + if (nr_pages == 0) > > > + break; > > > + ia = fuse_io_alloc(NULL, nr_pages); > > > + if (!ia) > > > + return; > > > + ap = &ia->ap; > > > + nr_pages = __readahead_batch(rac, ap->pages, nr_pages); > > > + for (i = 0; i < nr_pages; i++) { > > > + fuse_wait_on_page_writeback(inode, > > > + readahead_index(rac) + i); > > > > What's wrong with ap->pages[i]->index? Are we trying to wean off using ->index? > > It saves reading from a cacheline? I wouldn't be surprised if the > compiler hoisted the read from rac->_index to outside the loop and just > iterated from rac->_index to rac->_index + nr_pages. Hah, if such optimizations were worth anything with codepaths involving roundtrips to userspace... Anyway, I'll let these be, and maybe clean them up later. Acked-by: Miklos Szeredi <mszeredi@redhat.com> Thanks, Miklos
diff --git a/fs/fuse/file.c b/fs/fuse/file.c index 9d67b830fb7a..db82fb29dd39 100644 --- a/fs/fuse/file.c +++ b/fs/fuse/file.c @@ -915,84 +915,39 @@ static void fuse_send_readpages(struct fuse_io_args *ia, struct file *file) fuse_readpages_end(fc, &ap->args, err); } -struct fuse_fill_data { - struct fuse_io_args *ia; - struct file *file; - struct inode *inode; - unsigned int nr_pages; - unsigned int max_pages; -}; - -static int fuse_readpages_fill(void *_data, struct page *page) +static void fuse_readahead(struct readahead_control *rac) { - struct fuse_fill_data *data = _data; - struct fuse_io_args *ia = data->ia; - struct fuse_args_pages *ap = &ia->ap; - struct inode *inode = data->inode; + struct inode *inode = rac->mapping->host; struct fuse_conn *fc = get_fuse_conn(inode); + unsigned int i, max_pages, nr_pages = 0; - fuse_wait_on_page_writeback(inode, page->index); - - if (ap->num_pages && - (ap->num_pages == fc->max_pages || - (ap->num_pages + 1) * PAGE_SIZE > fc->max_read || - ap->pages[ap->num_pages - 1]->index + 1 != page->index)) { - data->max_pages = min_t(unsigned int, data->nr_pages, - fc->max_pages); - fuse_send_readpages(ia, data->file); - data->ia = ia = fuse_io_alloc(NULL, data->max_pages); - if (!ia) { - unlock_page(page); - return -ENOMEM; - } - ap = &ia->ap; - } - - if (WARN_ON(ap->num_pages >= data->max_pages)) { - unlock_page(page); - fuse_io_free(ia); - return -EIO; - } - - get_page(page); - ap->pages[ap->num_pages] = page; - ap->descs[ap->num_pages].length = PAGE_SIZE; - ap->num_pages++; - data->nr_pages--; - return 0; -} - -static int fuse_readpages(struct file *file, struct address_space *mapping, - struct list_head *pages, unsigned nr_pages) -{ - struct inode *inode = mapping->host; - struct fuse_conn *fc = get_fuse_conn(inode); - struct fuse_fill_data data; - int err; - - err = -EIO; if (is_bad_inode(inode)) - goto out; + return; - data.file = file; - data.inode = inode; - data.nr_pages = nr_pages; - data.max_pages = min_t(unsigned int, nr_pages, fc->max_pages); -; - data.ia = fuse_io_alloc(NULL, data.max_pages); - err = -ENOMEM; - if (!data.ia) - goto out; + max_pages = min(fc->max_pages, fc->max_read / PAGE_SIZE); - err = read_cache_pages(mapping, pages, fuse_readpages_fill, &data); - if (!err) { - if (data.ia->ap.num_pages) - fuse_send_readpages(data.ia, file); - else - fuse_io_free(data.ia); + for (;;) { + struct fuse_io_args *ia; + struct fuse_args_pages *ap; + + nr_pages = readahead_count(rac) - nr_pages; + if (nr_pages > max_pages) + nr_pages = max_pages; + if (nr_pages == 0) + break; + ia = fuse_io_alloc(NULL, nr_pages); + if (!ia) + return; + ap = &ia->ap; + nr_pages = __readahead_batch(rac, ap->pages, nr_pages); + for (i = 0; i < nr_pages; i++) { + fuse_wait_on_page_writeback(inode, + readahead_index(rac) + i); + ap->descs[i].length = PAGE_SIZE; + } + ap->num_pages = nr_pages; + fuse_send_readpages(ia, rac->file); } -out: - return err; } static ssize_t fuse_cache_read_iter(struct kiocb *iocb, struct iov_iter *to) @@ -3373,10 +3328,10 @@ static const struct file_operations fuse_file_operations = { static const struct address_space_operations fuse_file_aops = { .readpage = fuse_readpage, + .readahead = fuse_readahead, .writepage = fuse_writepage, .writepages = fuse_writepages, .launder_page = fuse_launder_page, - .readpages = fuse_readpages, .set_page_dirty = __set_page_dirty_nobuffers, .bmap = fuse_bmap, .direct_IO = fuse_direct_IO,