]> git.karo-electronics.de Git - linux-beck.git/commit
md/bitmap: optimise scanning of empty bitmaps.
authorNeilBrown <neilb@suse.de>
Tue, 1 Jun 2010 09:37:33 +0000 (19:37 +1000)
committerNeilBrown <neilb@suse.de>
Mon, 26 Jul 2010 03:21:32 +0000 (13:21 +1000)
commitef4256733506f2459a0c436b62267d22a3f0cec6
treec73e1849052f56a8f6033498f7fbd65c6259c776
parentb63d7c2e29bf9cc94989806f2df0cfca4976b830
md/bitmap: optimise scanning of empty bitmaps.

A bitmap is stored as one page per 2048 bits.
If none of the bits are set, the page is not allocated.

When bitmap_get_counter finds that a page isn't allocate,
it just reports that one bit work of space isn't flagged,
rather than reporting that 2048 bits worth of space are
unflagged.
This can cause searches for flagged bits (e.g. bitmap_close_sync)
to do more work than is really necessary.

So change bitmap_get_counter (when creating) to report a number of
blocks that more accurately reports the range of the device for which
no counter currently exists.

Signed-off-by: NeilBrown <neilb@suse.de>
drivers/md/bitmap.c