Commit 60c371bc authored Aug 05, 2006 by Andrew Morton Committed by Linus Torvalds Aug 06, 2006

[PATCH] fadvise() make POSIX_FADV_NOREUSE a no-op

The POSIX_FADV_NOREUSE hint means "the application will use this range of the
file a single time". It seems to be intended that the implementation will use
this hint to perform drop-behind of that part of the file when the application
gets around to reading or writing it.

However for reasons which aren't obvious (or sane?) I mapped
POSIX_FADV_NOREUSE onto POSIX_FADV_WILLNEED. ie: it does readahead.

That's daft. So for now, make POSIX_FADV_NOREUSE a no-op.

This is a non-back-compatible change. If someone was using POSIX_FADV_NOREUSE
to perform readahead, they lose. The likelihood is low.

If/when we later implement POSIX_FADV_NOREUSE things will get interesting - to
do it fully we'll need to maintain file offset/length ranges and peform all
sorts of complex tricks, and managing the lifetime of those ranges' data
structures will be interesting..

A sensible implementation would probably ignore the file range and would
simply mark the entire file as needing some form of drop-behind treatment.

Cc: Michael Kerrisk <mtk-manpages@gmx.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

parent bb39e419

mm/fadvise.c

+2 −1

Original line number	Diff line number	Diff line
		@@ -73,7 +73,6 @@ asmlinkage long sys_fadvise64_64(int fd, loff_t offset, loff_t len, int advice)
		file->f_ra.ra_pages = bdi->ra_pages * 2;
		break;
		case POSIX_FADV_WILLNEED:
		case POSIX_FADV_NOREUSE:
		if (!mapping->a_ops->readpage) {
		ret = -EINVAL;
		break;
		@@ -94,6 +93,8 @@ asmlinkage long sys_fadvise64_64(int fd, loff_t offset, loff_t len, int advice)
		if (ret > 0)
		ret = 0;
		break;
		case POSIX_FADV_NOREUSE:
		break;
		case POSIX_FADV_DONTNEED:
		if (!bdi_write_congested(mapping->backing_dev_info))
		filemap_flush(mapping);

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