Commit fb5527e6 authored by Jeff Moyer's avatar Jeff Moyer Committed by Linus Torvalds
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[PATCH] direct-io: sync and invalidate file region when falling back to buffered write 



When direct-io falls back to buffered write, it will just leave the dirty data
floating about in pagecache, pending regular writeback.

But normal direct-io semantics are that IO is synchronous, and that it leaves
no pagecache behind.

So change the fallback-to-buffered-write code to sync the file region and to
then strip away the pagecache, just as a regular direct-io write would do.

Acked-by: default avatarJeff Moyer <jmoyer@redhat.com>
Cc: Zach Brown <zach.brown@oracle.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent e8e82b76

mm/filemap.c

+45 −6
Original line number Diff line number Diff line
@@ -2222,7 +2222,7 @@ __generic_file_aio_write_nolock(struct kiocb *iocb, const struct iovec *iov, 
				unsigned long nr_segs, loff_t *ppos)

{

	struct file *file = iocb->ki_filp;

	const struct address_space * mapping = file->f_mapping;

	struct address_space * mapping = file->f_mapping;

	size_t ocount;		/* original count */

	size_t count;		/* after file limit checks */

	struct inode 	*inode = mapping->host;
@@ -2275,8 +2275,11 @@ __generic_file_aio_write_nolock(struct kiocb *iocb, const struct iovec *iov, 


	/* coalesce the iovecs and go direct-to-BIO for O_DIRECT */

	if (unlikely(file->f_flags & O_DIRECT)) {

		written = generic_file_direct_write(iocb, iov,

				&nr_segs, pos, ppos, count, ocount);

		loff_t endbyte;

		ssize_t written_buffered;



		written = generic_file_direct_write(iocb, iov, &nr_segs, pos,

							ppos, count, ocount);

		if (written < 0 || written == count)

			goto out;

		/*
@@ -2285,10 +2288,46 @@ __generic_file_aio_write_nolock(struct kiocb *iocb, const struct iovec *iov, 
		 */

		pos += written;

		count -= written;

		written_buffered = generic_file_buffered_write(iocb, iov,

						nr_segs, pos, ppos, count,

						written);

		/*

		 * If generic_file_buffered_write() retuned a synchronous error

		 * then we want to return the number of bytes which were

		 * direct-written, or the error code if that was zero.  Note

		 * that this differs from normal direct-io semantics, which

		 * will return -EFOO even if some bytes were written.

		 */

		if (written_buffered < 0) {

			err = written_buffered;

			goto out;

		}



		/*

		 * We need to ensure that the page cache pages are written to

		 * disk and invalidated to preserve the expected O_DIRECT

		 * semantics.

		 */

		endbyte = pos + written_buffered - written - 1;

		err = do_sync_file_range(file, pos, endbyte,

					 SYNC_FILE_RANGE_WAIT_BEFORE|

					 SYNC_FILE_RANGE_WRITE|

					 SYNC_FILE_RANGE_WAIT_AFTER);

		if (err == 0) {

			written = written_buffered;

			invalidate_mapping_pages(mapping,

						 pos >> PAGE_CACHE_SHIFT,

						 endbyte >> PAGE_CACHE_SHIFT);

		} else {

			/*

			 * We don't know how much we wrote, so just return

			 * the number of bytes which were direct-written

			 */

		}

	} else {

		written = generic_file_buffered_write(iocb, iov, nr_segs,

				pos, ppos, count, written);

	}

out:

	current->backing_dev_info = NULL;

	return written ? written : err;