| Message ID | 69fef253b37fc44dd28c43398715e27cee5e0fe0.1610170479.git.asml.silence@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | no-copy bvec | expand |
On Sat, Jan 09, 2021 at 04:03:03PM +0000, Pavel Begunkov wrote: > The block layer spends quite a while in blkdev_direct_IO() to copy and > initialise bio's bvec. However, if we've already got a bvec in the input > iterator it might be reused in some cases, i.e. when new > ITER_BVEC_FLAG_FIXED flag is set. Simple tests show considerable > performance boost, and it also reduces memory footprint. > > Suggested-by: Matthew Wilcox <willy@infradead.org> > Reviewed-by: Christoph Hellwig <hch@lst.de> > Signed-off-by: Pavel Begunkov <asml.silence@gmail.com> > --- > Documentation/filesystems/porting.rst | 9 ++++ > block/bio.c | 67 ++++++++++++--------------- > include/linux/bio.h | 5 +- > 3 files changed, 42 insertions(+), 39 deletions(-) > > diff --git a/Documentation/filesystems/porting.rst b/Documentation/filesystems/porting.rst > index c722d94f29ea..1f8cf8e10b34 100644 > --- a/Documentation/filesystems/porting.rst > +++ b/Documentation/filesystems/porting.rst > @@ -872,3 +872,12 @@ its result is kern_unmount() or kern_unmount_array(). > > zero-length bvec segments are disallowed, they must be filtered out before > passed on to an iterator. > + > +--- > + > +**mandatory** > + > +For bvec based itererators bio_iov_iter_get_pages() now doesn't copy bvecs but > +uses the one provided. Anyone issuing kiocb-I/O should ensure that the bvec and > +page references stay until I/O has completed, i.e. until ->ki_complete() has > +been called or returned with non -EIOCBQUEUED code. > diff --git a/block/bio.c b/block/bio.c > index 9f26984af643..6f031a04b59a 100644 > --- a/block/bio.c > +++ b/block/bio.c > @@ -960,21 +960,17 @@ void bio_release_pages(struct bio *bio, bool mark_dirty) > } > EXPORT_SYMBOL_GPL(bio_release_pages); > > -static int __bio_iov_bvec_add_pages(struct bio *bio, struct iov_iter *iter) > +static int bio_iov_bvec_set(struct bio *bio, struct iov_iter *iter) > { > - const struct bio_vec *bv = iter->bvec; > - unsigned int len; > - size_t size; > - > - if (WARN_ON_ONCE(iter->iov_offset > bv->bv_len)) > - return -EINVAL; > - > - len = min_t(size_t, bv->bv_len - iter->iov_offset, iter->count); > - size = bio_add_page(bio, bv->bv_page, len, > - bv->bv_offset + iter->iov_offset); > - if (unlikely(size != len)) > - return -EINVAL; > - iov_iter_advance(iter, size); > + WARN_ON_ONCE(BVEC_POOL_IDX(bio) != 0); > + > + bio->bi_vcnt = iter->nr_segs; > + bio->bi_max_vecs = iter->nr_segs; > + bio->bi_io_vec = (struct bio_vec *)iter->bvec; > + bio->bi_iter.bi_bvec_done = iter->iov_offset; > + bio->bi_iter.bi_size = iter->count; > + > + iov_iter_advance(iter, iter->count); > return 0; > } > > @@ -1088,12 +1084,12 @@ static int __bio_iov_append_get_pages(struct bio *bio, struct iov_iter *iter) > * This takes either an iterator pointing to user memory, or one pointing to > * kernel pages (BVEC iterator). If we're adding user pages, we pin them and > * map them into the kernel. On IO completion, the caller should put those > - * pages. If we're adding kernel pages, and the caller told us it's safe to > - * do so, we just have to add the pages to the bio directly. We don't grab an > - * extra reference to those pages (the user should already have that), and we > - * don't put the page on IO completion. The caller needs to check if the bio is > - * flagged BIO_NO_PAGE_REF on IO completion. If it isn't, then pages should be > - * released. > + * pages. For bvec based iterators bio_iov_iter_get_pages() uses the provided > + * bvecs rather than copying them. Hence anyone issuing kiocb based IO needs > + * to ensure the bvecs and pages stay referenced until the submitted I/O is > + * completed by a call to ->ki_complete() or returns with an error other than > + * -EIOCBQUEUED. The caller needs to check if the bio is flagged BIO_NO_PAGE_REF > + * on IO completion. If it isn't, then pages should be released. > * > * The function tries, but does not guarantee, to pin as many pages as > * fit into the bio, or are requested in @iter, whatever is smaller. If > @@ -1105,27 +1101,22 @@ static int __bio_iov_append_get_pages(struct bio *bio, struct iov_iter *iter) > */ > int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter) > { > - const bool is_bvec = iov_iter_is_bvec(iter); > - int ret; > - > - if (WARN_ON_ONCE(bio->bi_vcnt)) > - return -EINVAL; > + int ret = 0; > > - do { > - if (bio_op(bio) == REQ_OP_ZONE_APPEND) { > - if (WARN_ON_ONCE(is_bvec)) > - return -EINVAL; > - ret = __bio_iov_append_get_pages(bio, iter); > - } else { > - if (is_bvec) > - ret = __bio_iov_bvec_add_pages(bio, iter); > + if (iov_iter_is_bvec(iter)) { > + if (WARN_ON_ONCE(bio_op(bio) == REQ_OP_ZONE_APPEND)) > + return -EINVAL; > + bio_iov_bvec_set(bio, iter); > + bio_set_flag(bio, BIO_NO_PAGE_REF); > + return 0; > + } else { > + do { > + if (bio_op(bio) == REQ_OP_ZONE_APPEND) > + ret = __bio_iov_append_get_pages(bio, iter); > else > ret = __bio_iov_iter_get_pages(bio, iter); > - } > - } while (!ret && iov_iter_count(iter) && !bio_full(bio, 0)); > - > - if (is_bvec) > - bio_set_flag(bio, BIO_NO_PAGE_REF); > + } while (!ret && iov_iter_count(iter) && !bio_full(bio, 0)); > + } > > /* don't account direct I/O as memory stall */ > bio_clear_flag(bio, BIO_WORKINGSET); > diff --git a/include/linux/bio.h b/include/linux/bio.h > index d8f9077c43ef..1d30572a8c53 100644 > --- a/include/linux/bio.h > +++ b/include/linux/bio.h > @@ -444,10 +444,13 @@ static inline void bio_wouldblock_error(struct bio *bio) > > /* > * Calculate number of bvec segments that should be allocated to fit data > - * pointed by @iter. > + * pointed by @iter. If @iter is backed by bvec it's going to be reused > + * instead of allocating a new one. > */ > static inline int bio_iov_vecs_to_alloc(struct iov_iter *iter, int max_segs) > { > + if (iov_iter_is_bvec(iter)) > + return 0; > return iov_iter_npages(iter, max_segs); > } > > -- > 2.24.0 > Reviewed-by: Ming Lei <ming.lei@redhat.com>
diff --git a/Documentation/filesystems/porting.rst b/Documentation/filesystems/porting.rst index c722d94f29ea..1f8cf8e10b34 100644 --- a/Documentation/filesystems/porting.rst +++ b/Documentation/filesystems/porting.rst @@ -872,3 +872,12 @@ its result is kern_unmount() or kern_unmount_array(). zero-length bvec segments are disallowed, they must be filtered out before passed on to an iterator. + +--- + +**mandatory** + +For bvec based itererators bio_iov_iter_get_pages() now doesn't copy bvecs but +uses the one provided. Anyone issuing kiocb-I/O should ensure that the bvec and +page references stay until I/O has completed, i.e. until ->ki_complete() has +been called or returned with non -EIOCBQUEUED code. diff --git a/block/bio.c b/block/bio.c index 9f26984af643..6f031a04b59a 100644 --- a/block/bio.c +++ b/block/bio.c @@ -960,21 +960,17 @@ void bio_release_pages(struct bio *bio, bool mark_dirty) } EXPORT_SYMBOL_GPL(bio_release_pages); -static int __bio_iov_bvec_add_pages(struct bio *bio, struct iov_iter *iter) +static int bio_iov_bvec_set(struct bio *bio, struct iov_iter *iter) { - const struct bio_vec *bv = iter->bvec; - unsigned int len; - size_t size; - - if (WARN_ON_ONCE(iter->iov_offset > bv->bv_len)) - return -EINVAL; - - len = min_t(size_t, bv->bv_len - iter->iov_offset, iter->count); - size = bio_add_page(bio, bv->bv_page, len, - bv->bv_offset + iter->iov_offset); - if (unlikely(size != len)) - return -EINVAL; - iov_iter_advance(iter, size); + WARN_ON_ONCE(BVEC_POOL_IDX(bio) != 0); + + bio->bi_vcnt = iter->nr_segs; + bio->bi_max_vecs = iter->nr_segs; + bio->bi_io_vec = (struct bio_vec *)iter->bvec; + bio->bi_iter.bi_bvec_done = iter->iov_offset; + bio->bi_iter.bi_size = iter->count; + + iov_iter_advance(iter, iter->count); return 0; } @@ -1088,12 +1084,12 @@ static int __bio_iov_append_get_pages(struct bio *bio, struct iov_iter *iter) * This takes either an iterator pointing to user memory, or one pointing to * kernel pages (BVEC iterator). If we're adding user pages, we pin them and * map them into the kernel. On IO completion, the caller should put those - * pages. If we're adding kernel pages, and the caller told us it's safe to - * do so, we just have to add the pages to the bio directly. We don't grab an - * extra reference to those pages (the user should already have that), and we - * don't put the page on IO completion. The caller needs to check if the bio is - * flagged BIO_NO_PAGE_REF on IO completion. If it isn't, then pages should be - * released. + * pages. For bvec based iterators bio_iov_iter_get_pages() uses the provided + * bvecs rather than copying them. Hence anyone issuing kiocb based IO needs + * to ensure the bvecs and pages stay referenced until the submitted I/O is + * completed by a call to ->ki_complete() or returns with an error other than + * -EIOCBQUEUED. The caller needs to check if the bio is flagged BIO_NO_PAGE_REF + * on IO completion. If it isn't, then pages should be released. * * The function tries, but does not guarantee, to pin as many pages as * fit into the bio, or are requested in @iter, whatever is smaller. If @@ -1105,27 +1101,22 @@ static int __bio_iov_append_get_pages(struct bio *bio, struct iov_iter *iter) */ int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter) { - const bool is_bvec = iov_iter_is_bvec(iter); - int ret; - - if (WARN_ON_ONCE(bio->bi_vcnt)) - return -EINVAL; + int ret = 0; - do { - if (bio_op(bio) == REQ_OP_ZONE_APPEND) { - if (WARN_ON_ONCE(is_bvec)) - return -EINVAL; - ret = __bio_iov_append_get_pages(bio, iter); - } else { - if (is_bvec) - ret = __bio_iov_bvec_add_pages(bio, iter); + if (iov_iter_is_bvec(iter)) { + if (WARN_ON_ONCE(bio_op(bio) == REQ_OP_ZONE_APPEND)) + return -EINVAL; + bio_iov_bvec_set(bio, iter); + bio_set_flag(bio, BIO_NO_PAGE_REF); + return 0; + } else { + do { + if (bio_op(bio) == REQ_OP_ZONE_APPEND) + ret = __bio_iov_append_get_pages(bio, iter); else ret = __bio_iov_iter_get_pages(bio, iter); - } - } while (!ret && iov_iter_count(iter) && !bio_full(bio, 0)); - - if (is_bvec) - bio_set_flag(bio, BIO_NO_PAGE_REF); + } while (!ret && iov_iter_count(iter) && !bio_full(bio, 0)); + } /* don't account direct I/O as memory stall */ bio_clear_flag(bio, BIO_WORKINGSET); diff --git a/include/linux/bio.h b/include/linux/bio.h index d8f9077c43ef..1d30572a8c53 100644 --- a/include/linux/bio.h +++ b/include/linux/bio.h @@ -444,10 +444,13 @@ static inline void bio_wouldblock_error(struct bio *bio) /* * Calculate number of bvec segments that should be allocated to fit data - * pointed by @iter. + * pointed by @iter. If @iter is backed by bvec it's going to be reused + * instead of allocating a new one. */ static inline int bio_iov_vecs_to_alloc(struct iov_iter *iter, int max_segs) { + if (iov_iter_is_bvec(iter)) + return 0; return iov_iter_npages(iter, max_segs); }