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fs: return if direct I/O will trigger writeback

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Find out if the I/O will trigger a wait due to writeback. If yes,
return -EAGAIN.

Return -EINVAL for buffered AIO: there are multiple causes of
delay such as page locks, dirty throttling logic, page loading
from disk etc. which cannot be taken care of.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Goldwyn Rodrigues 2017-06-20 07:05:44 -05:00 committed by Jens Axboe
parent b745fafaf7
commit 6be96d3ad3
1 changed files with 25 additions and 7 deletions
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32
mm/filemap.c
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@ -2070,10 +2070,17 @@ generic_file_read_iter(struct kiocb *iocb, struct iov_iter *iter)
loff_t size;
size = i_size_read(inode);
retval = filemap_write_and_wait_range(mapping, iocb->ki_pos,
iocb->ki_pos + count - 1);
if (retval < 0)
goto out;
if (iocb->ki_flags & IOCB_NOWAIT) {
if (filemap_range_has_page(mapping, iocb->ki_pos,
iocb->ki_pos + count - 1))
return -EAGAIN;
} else {
retval = filemap_write_and_wait_range(mapping,
iocb->ki_pos,
iocb->ki_pos + count - 1);
if (retval < 0)
goto out;
}
file_accessed(file);
@ -2674,6 +2681,9 @@ inline ssize_t generic_write_checks(struct kiocb *iocb, struct iov_iter *from)
pos = iocb->ki_pos;
if ((iocb->ki_flags & IOCB_NOWAIT) && !(iocb->ki_flags & IOCB_DIRECT))
return -EINVAL;
if (limit != RLIM_INFINITY) {
if (iocb->ki_pos >= limit) {
send_sig(SIGXFSZ, current, 0);
@ -2742,9 +2752,17 @@ generic_file_direct_write(struct kiocb *iocb, struct iov_iter *from)
write_len = iov_iter_count(from);
end = (pos + write_len - 1) >> PAGE_SHIFT;
written = filemap_write_and_wait_range(mapping, pos, pos + write_len - 1);
if (written)
goto out;
if (iocb->ki_flags & IOCB_NOWAIT) {
/* If there are pages to writeback, return */
if (filemap_range_has_page(inode->i_mapping, pos,
pos + iov_iter_count(from)))
return -EAGAIN;
} else {
written = filemap_write_and_wait_range(mapping, pos,
pos + write_len - 1);
if (written)
goto out;
}
/*
* After a write we want buffered reads to be sure to go to disk to get