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Subject[PATCH] mm/filemap: don't revert iter on -EIOCBQUEUED
Date
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.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
mm/filemap.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index 5bc672d30143..2e1686e09425 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2633,7 +2633,8 @@ generic_file_read_iter(struct kiocb *iocb, struct iov_iter *iter)
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
@@ -3458,7 +3459,8 @@ generic_file_direct_write(struct kiocb *iocb, struct iov_iter *from)
}
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;
}
--
2.24.0
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