From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail190.messagelabs.com (mail190.messagelabs.com [216.82.249.51]) by kanga.kvack.org (Postfix) with SMTP id BF6396B007E for ; Mon, 2 Nov 2009 11:50:39 -0500 (EST) Date: Mon, 2 Nov 2009 16:50:33 +0000 (GMT) From: Hugh Dickins Subject: [PATCH] mm: remove incorrect swap_count() from try_to_unuse() Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org To: Linus Torvalds Cc: Bo Liu , Bob Liu , Andrew Morton , KAMEZAWA Hiroyuki , linux-mm@kvack.org, linux-kernel@vger.kernel.org List-ID: From: Bo Liu 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 Cc: stable@kernel.org --- mm/swapfile.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) --- 2.6.32-rc5/mm/swapfile.c 2009-10-05 04:20:31.000000000 +0100 +++ linux/mm/swapfile.c 2009-10-28 19:31:43.000000000 +0000 @@ -1151,8 +1151,7 @@ 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; -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org