tree ae99a8cb55b4d2716847521953db4bddd66b8e8b
parent 48aae42556e5ea1ba0d8ddab25352706577af2ed
author Nick Piggin <npiggin@suse.de> 1231281622 -0800
committer Linus Torvalds <torvalds@linux-foundation.org> 1231286349 -0800

mm: direct IO starvation improvement

Direct IO can invalidate and sync a lot of pagecache pages in the mapping.
 A 4K direct IO will actually try to sync and/or invalidate the pagecache
of the entire file, for example (which might be many GB or TB large).

Improve this by doing range syncs.  Also, memory no longer has to be
unmapped to catch the dirty bits for syncing, as dirty bits would remain
coherent due to dirty mmap accounting.

This fixes the immediate DM deadlocks when doing direct IO reads to block
device with a mounted filesystem, if only by papering over the problem
somewhat rather than addressing the fsync starvation cases.

Signed-off-by: Nick Piggin <npiggin@suse.de>
Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>