From: KOSAKI Motohiro Subject: Re: [PATCH] mm: vmscan: Correctly check if reclaimer should schedule during shrink_slab Date: Wed, 18 May 2011 09:45:59 +0900 Message-ID: <4DD316C7.60003@jp.fujitsu.com> References: <1305295404-12129-5-git-send-email-mgorman@suse.de> <4DCFAA80.7040109@jp.fujitsu.com> <1305519711.4806.7.camel@mulgrave.site> <20110516084558.GE5279@suse.de> <20110516102753.GF5279@suse.de> <20110517103840.GL5279@suse.de> <1305640239.2046.27.camel@lenovo> <20110517161508.GN5279@suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 7bit Cc: akpm@linux-foundation.org, minchan.kim@gmail.com, colin.king@canonical.com, James.Bottomley@hansenpartnership.com, raghu.prabhu13@gmail.com, jack@suse.cz, chris.mason@oracle.com, cl@linux.com, penberg@kernel.org, riel@redhat.com, hannes@cmpxchg.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-ext4@vger.kernel.org To: mgorman@suse.de Return-path: Received: from fgwmail5.fujitsu.co.jp ([192.51.44.35]:35139 "EHLO fgwmail5.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932188Ab1ERAqS (ORCPT ); Tue, 17 May 2011 20:46:18 -0400 In-Reply-To: <20110517161508.GN5279@suse.de> Sender: linux-ext4-owner@vger.kernel.org List-ID: (2011/05/18 1:15), Mel Gorman wrote: > It has been reported on some laptops that kswapd is consuming large > amounts of CPU and not being scheduled when SLUB is enabled during > large amounts of file copying. It is expected that this is due to > kswapd missing every cond_resched() point because; > > shrink_page_list() calls cond_resched() if inactive pages were isolated > which in turn may not happen if all_unreclaimable is set in > shrink_zones(). If for whatver reason, all_unreclaimable is > set on all zones, we can miss calling cond_resched(). > > balance_pgdat() only calls cond_resched if the zones are not > balanced. For a high-order allocation that is balanced, it > checks order-0 again. During that window, order-0 might have > become unbalanced so it loops again for order-0 and returns > that it was reclaiming for order-0 to kswapd(). It can then > find that a caller has rewoken kswapd for a high-order and > re-enters balance_pgdat() without ever calling cond_resched(). > > shrink_slab only calls cond_resched() if we are reclaiming slab > pages. If there are a large number of direct reclaimers, the > shrinker_rwsem can be contended and prevent kswapd calling > cond_resched(). > > This patch modifies the shrink_slab() case. If the semaphore is > contended, the caller will still check cond_resched(). After each > successful call into a shrinker, the check for cond_resched() is > still necessary in case one shrinker call is particularly slow. > > This patch replaces > mm-vmscan-if-kswapd-has-been-running-too-long-allow-it-to-sleep.patch > in -mm. > > [mgorman@suse.de: Preserve call to cond_resched after each call into shrinker] > From: Minchan Kim > Signed-off-by: Mel Gorman Looks good to me. Reviewed-by: KOSAKI Motohiro