| Message ID | 498b34d746627e874740d8315b2924880c46dbc3.1607976425.git.asml.silence@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | no-copy bvec | expand |
On Tue, Dec 15, 2020 at 12:20:25AM +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> > Signed-off-by: Pavel Begunkov <asml.silence@gmail.com> > --- > Documentation/filesystems/porting.rst | 9 ++++ > block/bio.c | 64 +++++++++++---------------- > include/linux/bio.h | 3 ++ > 3 files changed, 38 insertions(+), 38 deletions(-) This doesn't touch iomap code, so the title of the patch seems wrong... > +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. This is hard to follow. Perhaps: bio_iov_iter_get_pages() uses the bvecs provided for bvec based iterators 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. > diff --git a/include/linux/bio.h b/include/linux/bio.h > index 2a9f3f0bbe0a..337f4280b639 100644 > --- a/include/linux/bio.h > +++ b/include/linux/bio.h > @@ -444,6 +444,9 @@ static inline void bio_wouldblock_error(struct bio *bio) > > static inline int bio_iov_vecs_to_alloc(struct iov_iter *iter, int max_segs) > { > + /* reuse iter->bvec */ > + if (iov_iter_is_bvec(iter)) > + return 0; > return iov_iter_npages(iter, max_segs); Ah, I'm a blind idiot... :/ Cheers, Dave.
On 15/12/2020 01:09, Dave Chinner wrote: > On Tue, Dec 15, 2020 at 12:20:25AM +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> >> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com> >> --- >> Documentation/filesystems/porting.rst | 9 ++++ >> block/bio.c | 64 +++++++++++---------------- >> include/linux/bio.h | 3 ++ >> 3 files changed, 38 insertions(+), 38 deletions(-) > > This doesn't touch iomap code, so the title of the patch seems > wrong... yeah, should be bio. > >> +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. > > This is hard to follow. Perhaps: > > bio_iov_iter_get_pages() uses the bvecs provided for bvec based > iterators 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. Agree, that's easier to read, thanks > >> diff --git a/include/linux/bio.h b/include/linux/bio.h >> index 2a9f3f0bbe0a..337f4280b639 100644 >> --- a/include/linux/bio.h >> +++ b/include/linux/bio.h >> @@ -444,6 +444,9 @@ static inline void bio_wouldblock_error(struct bio *bio) >> >> static inline int bio_iov_vecs_to_alloc(struct iov_iter *iter, int max_segs) >> { >> + /* reuse iter->bvec */ >> + if (iov_iter_is_bvec(iter)) >> + return 0; >> return iov_iter_npages(iter, max_segs); > > Ah, I'm a blind idiot... :/ > > Cheers, > > Dave. >
On Tue, Dec 15, 2020 at 12:20:25AM +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> > Signed-off-by: Pavel Begunkov <asml.silence@gmail.com> > --- > Documentation/filesystems/porting.rst | 9 ++++ > block/bio.c | 64 +++++++++++---------------- > include/linux/bio.h | 3 ++ > 3 files changed, 38 insertions(+), 38 deletions(-) > > diff --git a/Documentation/filesystems/porting.rst b/Documentation/filesystems/porting.rst > index 867036aa90b8..47a622879952 100644 > --- a/Documentation/filesystems/porting.rst > +++ b/Documentation/filesystems/porting.rst > @@ -865,3 +865,12 @@ no matter what. Everything is handled by the caller. > > clone_private_mount() returns a longterm mount now, so the proper destructor of > its result is kern_unmount() or kern_unmount_array(). > + > +--- > + > +**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 3192358c411f..f8229be24562 100644 > --- a/block/bio.c > +++ b/block/bio.c > @@ -960,25 +960,16 @@ void bio_release_pages(struct bio *bio, bool mark_dirty) > } > EXPORT_SYMBOL_GPL(bio_release_pages); > > +static int bio_iov_bvec_set(struct bio *bio, struct iov_iter *iter) > { > + 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; Nit: I find an empty liner after WARN_ON_ONCE that assert the caller state very helpful when reading the code. > static inline int bio_iov_vecs_to_alloc(struct iov_iter *iter, int max_segs) > { > + /* reuse iter->bvec */ Maybe add a ", see bio_iov_bvec_set for details" here?
diff --git a/Documentation/filesystems/porting.rst b/Documentation/filesystems/porting.rst index 867036aa90b8..47a622879952 100644 --- a/Documentation/filesystems/porting.rst +++ b/Documentation/filesystems/porting.rst @@ -865,3 +865,12 @@ no matter what. Everything is handled by the caller. clone_private_mount() returns a longterm mount now, so the proper destructor of its result is kern_unmount() or kern_unmount_array(). + +--- + +**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 3192358c411f..f8229be24562 100644 --- a/block/bio.c +++ b/block/bio.c @@ -960,25 +960,16 @@ 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; - struct page *page = bv->bv_page; - bool same_page = false; - unsigned int off, len; - - 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); - off = bv->bv_offset + iter->iov_offset; - - if (!__bio_try_merge_page(bio, page, len, off, &same_page)) { - if (bio_full(bio, len)) - return -EINVAL; - bio_add_page_noaccount(bio, page, len, off); - } - iov_iter_advance(iter, len); + 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; } @@ -1092,12 +1083,13 @@ 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. If we're adding kernel pages, it doesn't take extra page references + * and reuses the provided bvec, so the caller must ensure that the bvec isn't + * freed and page references remain to be taken until I/O has completed. If + * the I/O is completed asynchronously, the bvec must not be freed before + * ->ki_complete() has been called. 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 @@ -1109,27 +1101,23 @@ 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; + 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; + } do { - if (bio_op(bio) == REQ_OP_ZONE_APPEND) { - if (WARN_ON_ONCE(is_bvec)) - return -EINVAL; + if (bio_op(bio) == REQ_OP_ZONE_APPEND) ret = __bio_iov_append_get_pages(bio, iter); - } else { - if (is_bvec) - ret = __bio_iov_bvec_add_pages(bio, iter); - else - ret = __bio_iov_iter_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); return bio->bi_vcnt ? 0 : ret; } EXPORT_SYMBOL_GPL(bio_iov_iter_get_pages); diff --git a/include/linux/bio.h b/include/linux/bio.h index 2a9f3f0bbe0a..337f4280b639 100644 --- a/include/linux/bio.h +++ b/include/linux/bio.h @@ -444,6 +444,9 @@ static inline void bio_wouldblock_error(struct bio *bio) static inline int bio_iov_vecs_to_alloc(struct iov_iter *iter, int max_segs) { + /* reuse iter->bvec */ + if (iov_iter_is_bvec(iter)) + return 0; return iov_iter_npages(iter, max_segs); }
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> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com> --- Documentation/filesystems/porting.rst | 9 ++++ block/bio.c | 64 +++++++++++---------------- include/linux/bio.h | 3 ++ 3 files changed, 38 insertions(+), 38 deletions(-)