2.6.31-stable review patch. If anyone has any objections, please let us know. ------------------ From: Bo Liu commit 32c5fc10e79a7053ac5728b01a0bff55cbcb9d49 upstream. In try_to_unuse(), swcount is a local copy of *swap_map, including the SWAP_HAS_CACHE bit; but a wrong comparison against swap_count(*swap_map), which masks off the SWAP_HAS_CACHE bit, succeeded where it should fail. That had the effect of resetting the mm from which to start searching for the next swap page, to an irrelevant mm instead of to an mm in which this swap page had been found: which may increase search time by ~20%. But we're used to swapoff being slow, so never noticed the slowdown. Remove that one spurious use of swap_count(): Bo Liu thought it merely redundant, Hugh rewrote the description since it was measurably wrong. Signed-off-by: Bo Liu Signed-off-by: Hugh Dickins Reviewed-by: KAMEZAWA Hiroyuki Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- mm/swapfile.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -1149,8 +1149,7 @@ static int try_to_unuse(unsigned int typ } else retval = unuse_mm(mm, entry, page); - if (set_start_mm && - swap_count(*swap_map) < swcount) { + if (set_start_mm && *swap_map < swcount) { mmput(new_start_mm); atomic_inc(&mm->mm_users); new_start_mm = mm;