From: Pavel Begunkov <asml.silence@xxxxxxxxx>
Subject: mm/filemap: don't revert iter on -EIOCBQUEUED
Currently, if I/O is enqueued for async execution direct paths of
generic_file_{read,write}_iter() will always revert the iter. There are
no users expecting that, and that is also costly. Leave iterators as is
on -EIOCBQUEUED.
Link: https://lkml.kernel.org/r/f5247b60e7abbd2ff850cd108491f53a2e0c501a.1610207781.git.asml.silence@xxxxxxxxx
Signed-off-by: Pavel Begunkov <asml.silence@xxxxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/filemap.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
--- a/mm/filemap.c~mm-filemap-dont-revert-iter-on-eiocbqueued
+++ a/mm/filemap.c
@@ -2615,7 +2615,8 @@ generic_file_read_iter(struct kiocb *ioc
iocb->ki_pos += retval;
count -= retval;
}
- iov_iter_revert(iter, count - iov_iter_count(iter));
+ if (retval != -EIOCBQUEUED)
+ iov_iter_revert(iter, count - iov_iter_count(iter));
/*
* Btrfs can have a short DIO read if we encounter
@@ -3426,7 +3427,8 @@ generic_file_direct_write(struct kiocb *
}
iocb->ki_pos = pos;
}
- iov_iter_revert(from, write_len - iov_iter_count(from));
+ if (written != -EIOCBQUEUED)
+ iov_iter_revert(from, write_len - iov_iter_count(from));
out:
return written;
}
_
