From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754542AbZDVA02 (ORCPT ); Tue, 21 Apr 2009 20:26:28 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753835AbZDVA0Q (ORCPT ); Tue, 21 Apr 2009 20:26:16 -0400 Received: from fgwmail7.fujitsu.co.jp ([192.51.44.37]:46223 "EHLO fgwmail7.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753753AbZDVA0P (ORCPT ); Tue, 21 Apr 2009 20:26:15 -0400 From: KOSAKI Motohiro To: Mel Gorman Subject: Re: [PATCH 21/25] Use allocation flags as an index to the zone watermark Cc: kosaki.motohiro@jp.fujitsu.com, Linux Memory Management List , Christoph Lameter , Nick Piggin , Linux Kernel Mailing List , Lin Ming , Zhang Yanmin , Peter Zijlstra , Pekka Enberg , Andrew Morton In-Reply-To: <1240266011-11140-22-git-send-email-mel@csn.ul.ie> References: <1240266011-11140-1-git-send-email-mel@csn.ul.ie> <1240266011-11140-22-git-send-email-mel@csn.ul.ie> Message-Id: <20090422092429.6271.A69D9226@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit X-Mailer: Becky! ver. 2.50 [ja] Date: Wed, 22 Apr 2009 09:26:10 +0900 (JST) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > ALLOC_WMARK_MIN, ALLOC_WMARK_LOW and ALLOC_WMARK_HIGH determin whether > pages_min, pages_low or pages_high is used as the zone watermark when > allocating the pages. Two branches in the allocator hotpath determine which > watermark to use. This patch uses the flags as an array index and places > the three watermarks in a union with an array so it can be offset. This > means the flags can be used as an array index and reduces the branches > taken. > > Signed-off-by: Mel Gorman > Reviewed-by: Christoph Lameter > --- > include/linux/mmzone.h | 8 +++++++- > mm/page_alloc.c | 18 ++++++++---------- > 2 files changed, 15 insertions(+), 11 deletions(-) > > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h > index f82bdba..c1fa208 100644 > --- a/include/linux/mmzone.h > +++ b/include/linux/mmzone.h > @@ -275,7 +275,13 @@ struct zone_reclaim_stat { > > struct zone { > /* Fields commonly accessed by the page allocator */ > - unsigned long pages_min, pages_low, pages_high; > + union { > + struct { > + unsigned long pages_min, pages_low, pages_high; > + }; > + unsigned long pages_mark[3]; > + }; > + hmmm... I don't like union hack. Why can't we change all caller to use page_mark? > /* > * We don't know if the memory that we're going to allocate will be freeable > * or/and it will be released eventually, so to avoid totally wasting several > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 376d848..e61867e 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -1157,10 +1157,13 @@ failed: > return NULL; > } > > -#define ALLOC_NO_WATERMARKS 0x01 /* don't check watermarks at all */ > -#define ALLOC_WMARK_MIN 0x02 /* use pages_min watermark */ > -#define ALLOC_WMARK_LOW 0x04 /* use pages_low watermark */ > -#define ALLOC_WMARK_HIGH 0x08 /* use pages_high watermark */ > +/* The WMARK bits are used as an index zone->pages_mark */ > +#define ALLOC_WMARK_MIN 0x00 /* use pages_min watermark */ > +#define ALLOC_WMARK_LOW 0x01 /* use pages_low watermark */ > +#define ALLOC_WMARK_HIGH 0x02 /* use pages_high watermark */ > +#define ALLOC_NO_WATERMARKS 0x08 /* don't check watermarks at all */ > +#define ALLOC_WMARK_MASK 0x07 /* Mask to get the watermark bits */ the mask only use two bit. but mask definition is three bit (0x07), why? > + > #define ALLOC_HARDER 0x10 /* try to alloc harder */ > #define ALLOC_HIGH 0x20 /* __GFP_HIGH set */ > #ifdef CONFIG_CPUSETS > @@ -1463,12 +1466,7 @@ zonelist_scan: > > if (!(alloc_flags & ALLOC_NO_WATERMARKS)) { > unsigned long mark; > - if (alloc_flags & ALLOC_WMARK_MIN) > - mark = zone->pages_min; > - else if (alloc_flags & ALLOC_WMARK_LOW) > - mark = zone->pages_low; > - else > - mark = zone->pages_high; > + mark = zone->pages_mark[alloc_flags & ALLOC_WMARK_MASK]; > if (!zone_watermark_ok(zone, order, mark, > classzone_idx, alloc_flags)) { > if (!zone_reclaim_mode || > -- > 1.5.6.5 >