Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754077AbZLAMbG (ORCPT ); Tue, 1 Dec 2009 07:31:06 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753416AbZLAMbG (ORCPT ); Tue, 1 Dec 2009 07:31:06 -0500 Received: from fgwmail6.fujitsu.co.jp ([192.51.44.36]:49308 "EHLO fgwmail6.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753231AbZLAMbE (ORCPT ); Tue, 1 Dec 2009 07:31:04 -0500 X-SecurityPolicyCheck-FJ: OK by FujitsuOutboundMailChecker v1.3.1 From: KOSAKI Motohiro To: Andrea Arcangeli Subject: Re: [RFC] high system time & lock contention running large mixed workload Cc: kosaki.motohiro@jp.fujitsu.com, Larry Woodman , linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, Hugh Dickins , KAMEZAWA Hiroyuki , Rik van Riel In-Reply-To: <20091201100444.GN30235@random.random> References: <1259618429.2345.3.camel@dhcp-100-19-198.bos.redhat.com> <20091201100444.GN30235@random.random> Message-Id: <20091201212357.5C3A.A69D9226@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit X-Mailer: Becky! ver. 2.50.07 [ja] Date: Tue, 1 Dec 2009 21:31:09 +0900 (JST) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2392 Lines: 49 > On Mon, Nov 30, 2009 at 05:00:29PM -0500, Larry Woodman wrote: > > Before the splitLRU patch shrink_active_list() would only call > > page_referenced() when reclaim_mapped got set. reclaim_mapped only got > > set when the priority worked its way from 12 all the way to 7. This > > prevented page_referenced() from being called from shrink_active_list() > > until the system was really struggling to reclaim memory. > > page_referenced should never be called and nobody should touch ptes > until priority went down to 7. This is a regression in splitLRU that > should be fixed. With light VM pressure we should never touch ptes ever. Ummm. I can't agree this. 7 is too small priority. if large system have prio==7, the system have unacceptable big latency trouble. if only prio==DEF_PRIOTIRY or something, I can agree you probably. > > On way to prevent this is to change page_check_address() to execute a > > spin_trylock(ptl) when it was called by shrink_active_list() and simply > > fail if it could not get the pte_lockptr spinlock. This will make > > shrink_active_list() consider the page not referenced and allow the > > anon_vma->lock to be dropped much quicker. > > > > The attached patch does just that, thoughts??? > > Just stop calling page_referenced there... > > Even if we ignore the above, one problem later in skipping over the PT > lock, is also to assume the page is not referenced when it actually > is, so it won't be activated again when page_referenced is called > again to move the page back in the active list... Not the end of the > world to lose a young bit sometime though. > > There may be all reasons in the world why we have to mess with ptes > when there's light VM pressure, for whatever terabyte machine or > whatever workload that performs better that way, but I know in 100% of > my systems I don't ever want the VM to touch ptes when there's light > VM pressure, no matter what. So if you want the default to be messing > with ptes, just give me a sysctl knob to let me run faster. Um. Avoiding lock contention on light VM pressure is important than strict lru order. I guess we don't need knob. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/