path: root/Documentation/filesystems
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authorPavel Begunkov <>2021-01-09 16:03:03 +0000
committerJens Axboe <>2021-01-25 08:58:24 -0700
commitc42bca92be928ce7dece5fc04cf68d0e37ee6718 (patch)
tree132b3485f416fde3c9d57e9003f826fcb5583d75 /Documentation/filesystems
parent3e1a88ec96259282b9a8b45c3f1fda7a3ff4f6ea (diff)
bio: don't copy bvec for direct IO
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 <> Reviewed-by: Christoph Hellwig <> Signed-off-by: Pavel Begunkov <> Reviewed-by: Ming Lei <> Signed-off-by: Jens Axboe <>
Diffstat (limited to 'Documentation/filesystems')
1 files changed, 9 insertions, 0 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.
+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.