From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ee0-f51.google.com (mail-ee0-f51.google.com [74.125.83.51]) by kanga.kvack.org (Postfix) with ESMTP id D02426B0044 for ; Thu, 1 May 2014 04:44:58 -0400 (EDT) Received: by mail-ee0-f51.google.com with SMTP id c13so2057471eek.24 for ; Thu, 01 May 2014 01:44:58 -0700 (PDT) Received: from mx2.suse.de (cantor2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id r9si33491183eew.258.2014.05.01.01.44.57 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Thu, 01 May 2014 01:44:57 -0700 (PDT) From: Mel Gorman Subject: [PATCH 07/17] mm: page_alloc: Take the ALLOC_NO_WATERMARK check out of the fast path Date: Thu, 1 May 2014 09:44:38 +0100 Message-Id: <1398933888-4940-8-git-send-email-mgorman@suse.de> In-Reply-To: <1398933888-4940-1-git-send-email-mgorman@suse.de> References: <1398933888-4940-1-git-send-email-mgorman@suse.de> Sender: owner-linux-mm@kvack.org List-ID: To: Linux-MM , Linux-FSDevel Cc: Johannes Weiner , Vlastimil Babka , Jan Kara , Michal Hocko , Hugh Dickins , Mel Gorman , Linux Kernel ALLOC_NO_WATERMARK is set in a few cases. Always by kswapd, always for __GFP_MEMALLOC, sometimes for swap-over-nfs, tasks etc. Each of these cases are relatively rare events but the ALLOC_NO_WATERMARK check is an unlikely branch in the fast path. This patch moves the check out of the fast path and after it has been determined that the watermarks have not been met. This helps the common fast path at the cost of making the slow path slower and hitting kswapd with a performance cost. It's a reasonable tradeoff. Signed-off-by: Mel Gorman Acked-by: Johannes Weiner --- mm/page_alloc.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 2e576fd..dc123ff 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -1944,9 +1944,6 @@ zonelist_scan: (alloc_flags & ALLOC_CPUSET) && !cpuset_zone_allowed_softwall(zone, gfp_mask)) continue; - BUILD_BUG_ON(ALLOC_NO_WATERMARKS < NR_WMARK); - if (unlikely(alloc_flags & ALLOC_NO_WATERMARKS)) - goto try_this_zone; /* * Distribute pages in proportion to the individual * zone size to ensure fair page aging. The zone a @@ -1993,6 +1990,11 @@ zonelist_scan: classzone_idx, alloc_flags)) { int ret; + /* Checked here to keep the fast path fast */ + BUILD_BUG_ON(ALLOC_NO_WATERMARKS < NR_WMARK); + if (alloc_flags & ALLOC_NO_WATERMARKS) + goto try_this_zone; + if (IS_ENABLED(CONFIG_NUMA) && !did_zlc_setup && nr_online_nodes > 1) { /* -- 1.8.4.5 -- 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