Commit 6be96d3a authored by Goldwyn Rodrigues's avatar Goldwyn Rodrigues Committed by Jens Axboe
Browse files

fs: return if direct I/O will trigger writeback 



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: default avatarChristoph Hellwig <hch@lst.de>
Reviewed-by: default avatarJan Kara <jack@suse.cz>
Signed-off-by: default avatarGoldwyn Rodrigues <rgoldwyn@suse.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent b745fafa

mm/filemap.c

+25 −7
Original line number Diff line number Diff line
@@ -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,

		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 (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

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