From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755771Ab0GILEn (ORCPT ); Fri, 9 Jul 2010 07:04:43 -0400 Received: from fgwmail7.fujitsu.co.jp ([192.51.44.37]:55388 "EHLO fgwmail7.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755302Ab0GILEm convert rfc822-to-8bit (ORCPT ); Fri, 9 Jul 2010 07:04:42 -0400 X-SecurityPolicyCheck-FJ: OK by FujitsuOutboundMailChecker v1.3.1 From: KOSAKI Motohiro To: Minchan Kim Subject: Re: [PATCH] vmscan: stop meaningless loop iteration when no reclaimable slab Cc: kosaki.motohiro@jp.fujitsu.com, Andrew Morton , Christoph Lameter , LKML , linux-mm , Mel Gorman , Rik van Riel , Johannes Weiner In-Reply-To: References: <20100709191308.FA25.A69D9226@jp.fujitsu.com> Message-Id: <20100709195625.FA28.A69D9226@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 8BIT X-Mailer: Becky! ver. 2.50.07 [ja] Date: Fri, 9 Jul 2010 20:04:36 +0900 (JST) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On Fri, Jul 9, 2010 at 7:13 PM, KOSAKI Motohiro > wrote: > > If number of reclaimable slabs are zero, shrink_icache_memory() and > > shrink_dcache_memory() return 0. but strangely shrink_slab() ignore > > it and continue meaningless loop iteration. > > > > This patch fixes it. > > > > Signed-off-by: KOSAKI Motohiro > > --- > >  mm/vmscan.c |    5 +++++ > >  1 files changed, 5 insertions(+), 0 deletions(-) > > > > diff --git a/mm/vmscan.c b/mm/vmscan.c > > index 0f9f624..8f61adb 100644 > > --- a/mm/vmscan.c > > +++ b/mm/vmscan.c > > @@ -243,6 +243,11 @@ unsigned long shrink_slab(unsigned long scanned, gfp_t gfp_mask, > >                        int nr_before; > > > >                        nr_before = (*shrinker->shrink)(0, gfp_mask); > > +                       /* no slab objects, no more reclaim. */ > > +                       if (nr_before == 0) { > > +                               total_scan = 0; > > Why do you reset totoal_scan to 0? If shab objects are zero, we don't need more reclaim. > I don't know exact meaning of shrinker->nr. similar meaning of reclaim_stat->nr_saved_scan. If total_scan can't divide SHRINK_BATCH(128), saving remainder and using at next shrink_slab(). > AFAIU, it can affect next shrinker's total_scan. > Isn't it harmful? No. This loop is total_scan = shrinker->nr; /* Reset and init total_scan */ shrinker->nr = 0; while (total_scan >= SHRINK_BATCH) { nr_before = (*shrinker->shrink)(0, gfp_mask); /* no slab objects, no more reclaim. */ if (nr_before == 0) { total_scan = 0; break; } shrink_ret = (*shrinker->shrink)(this_scan, gfp_mask); if (shrink_ret == -1) break; if (shrink_ret < nr_before) ret += nr_before - shrink_ret; total_scan -= this_scan; } shrinker->nr += total_scan; /* save remainder #of-scan */