md: reduce CPU wastage on idle md array with a write-intent bitmap
authorNeilBrown <neilb@suse.de>
Tue, 4 Mar 2008 22:29:30 +0000 (14:29 -0800)
committerLinus Torvalds <torvalds@woody.linux-foundation.org>
Wed, 5 Mar 2008 00:35:17 +0000 (16:35 -0800)
commit8311c29d40235062a843f4a8e8a70a44af6fe4c9
treec869143fae8f135646300d1bac6639af5bb30dd7
parenta35e63efa1fb18c6f20f38e3ddf3f8ffbcf0f6e7
md: reduce CPU wastage on idle md array with a write-intent bitmap

On an md array with a write-intent bitmap, a thread wakes up every few seconds
and scans the bitmap looking for work to do.  If the array is idle, there will
be no work to do, but a lot of scanning is done to discover this.

So cache the fact that the bitmap is completely clean, and avoid scanning the
whole bitmap when the cache is known to be clean.

Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
drivers/md/bitmap.c
include/linux/raid/bitmap.h