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Date: Tue, 15 Dec 2020 00:20:19 +0000 From: Pavel Begunkov <asml.silence@...il.com> To: linux-block@...r.kernel.org Cc: Jens Axboe <axboe@...nel.dk>, Christoph Hellwig <hch@...radead.org>, Matthew Wilcox <willy@...radead.org>, Ming Lei <ming.lei@...hat.com>, Johannes Weiner <hannes@...xchg.org>, Alexander Viro <viro@...iv.linux.org.uk>, "Darrick J . Wong" <darrick.wong@...cle.com>, "Martin K . Petersen" <martin.petersen@...cle.com>, Jonathan Corbet <corbet@....net>, linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org, io-uring@...r.kernel.org, linux-kernel@...r.kernel.org, target-devel@...r.kernel.org, linux-scsi@...r.kernel.org, linux-doc@...r.kernel.org Subject: [PATCH v1 0/6] no-copy bvec Instead of creating a full copy of iter->bvec into bio in direct I/O, the patchset makes use of the one provided. It changes semantics and obliges users of asynchronous kiocb to track bvec lifetime, and [1/6] converts the only place that doesn't. bio_iov_iter_get_pages() is still does iov_iter_advance(), which is not great, but neccessary for revert to work. It's desirable to have a fast version of iov_iter_advance(i, i->count), so we may want to hack something up for that. E.g. allow to not keep it consistent in some cases when i->count==0. Also we can add a separate bio pool without inlined bvec. Very easy to do and shrinks bios from 3 to 2 cachelines. Also as suggested it removes BIO_WORKINGSET from direct paths: blkdev, iomap, fs/direct-io. Even though the last one is not very important as more filesystems are converted to iomap, but still looks hacky. Maybe, as Johannes mentioned in another thread, moving it to the writeback code (or other option) would be better in the end. Afterwards? since RFC: - add target_core_file patch by Christoph - make no-copy default behaviour, remove iter flag - iter_advance() instead of hacks to revert to work - add bvec iter_advance() optimisation patch - remove PSI annotations from direct IO (iomap, block and fs/direct) - note in d/f/porting Christoph Hellwig (1): target/file: allocate the bvec array as part of struct target_core_file_cmd Pavel Begunkov (5): iov_iter: optimise bvec iov_iter_advance() bio: deduplicate adding a page into bio block/psi: remove PSI annotations from direct IO bio: add a helper calculating nr segments to alloc block/iomap: don't copy bvec for direct IO Documentation/filesystems/porting.rst | 9 +++ block/bio.c | 103 ++++++++++++-------------- drivers/target/target_core_file.c | 20 ++--- fs/block_dev.c | 7 +- fs/direct-io.c | 2 + fs/iomap/direct-io.c | 9 +-- include/linux/bio.h | 9 +++ lib/iov_iter.c | 19 +++++ 8 files changed, 102 insertions(+), 76 deletions(-) -- 2.24.0
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