From: KOSAKI Motohiro Subject: Re: [PATCH 4/4] mm: vmscan: If kswapd has been running too long, allow it to sleep Date: Wed, 18 May 2011 09:26:09 +0900 Message-ID: <4DD31221.3060205@jp.fujitsu.com> References: <1305295404-12129-1-git-send-email-mgorman@suse.de> <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> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 7bit Cc: minchan.kim@gmail.com, James.Bottomley@hansenpartnership.com, akpm@linux-foundation.org, colin.king@canonical.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: In-Reply-To: <20110516102753.GF5279@suse.de> Sender: owner-linux-mm@kvack.org List-Id: linux-ext4.vger.kernel.org > Lets see; > > shrink_page_list() only applies 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(). > > shrink_slab only applies if we are reclaiming slab pages. If the first > shrinker returns -1, we do not call cond_resched(). If that > first shrinker is dcache and __GFP_FS is not set, direct > reclaimers will not shrink at all. However, if there are > enough of them running or if one of the other shrinkers > is running for a very long time, kswapd could be starved > acquiring the shrinker_rwsem and never reaching the > cond_resched(). OK. > > 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 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 have called cond_resched(). Then, Shouldn't balance_pgdat() call cond_resched() unconditionally? The problem is NOT 100% cpu consumption. if kswapd will sleep, other processes need to reclaim old pages. The problem is, kswapd doesn't invoke context switch and other tasks hang-up. > While it appears unlikely, there are bad conditions which can result > in cond_resched() being avoided. > -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org