From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail191.messagelabs.com (mail191.messagelabs.com [216.82.242.19]) by kanga.kvack.org (Postfix) with SMTP id A3475600786 for ; Tue, 1 Dec 2009 07:31:14 -0500 (EST) Received: from m4.gw.fujitsu.co.jp ([10.0.50.74]) by fgwmail5.fujitsu.co.jp (Fujitsu Gateway) with ESMTP id nB1CVA0s020004 for (envelope-from kosaki.motohiro@jp.fujitsu.com); Tue, 1 Dec 2009 21:31:10 +0900 Received: from smail (m4 [127.0.0.1]) by outgoing.m4.gw.fujitsu.co.jp (Postfix) with ESMTP id 6154D45DE6F for ; Tue, 1 Dec 2009 21:31:10 +0900 (JST) Received: from s4.gw.fujitsu.co.jp (s4.gw.fujitsu.co.jp [10.0.50.94]) by m4.gw.fujitsu.co.jp (Postfix) with ESMTP id 3EB4145DE6E for ; Tue, 1 Dec 2009 21:31:10 +0900 (JST) Received: from s4.gw.fujitsu.co.jp (localhost.localdomain [127.0.0.1]) by s4.gw.fujitsu.co.jp (Postfix) with ESMTP id 091961DB8041 for ; Tue, 1 Dec 2009 21:31:10 +0900 (JST) Received: from ml13.s.css.fujitsu.com (ml13.s.css.fujitsu.com [10.249.87.103]) by s4.gw.fujitsu.co.jp (Postfix) with ESMTP id AAE691DB803B for ; Tue, 1 Dec 2009 21:31:09 +0900 (JST) From: KOSAKI Motohiro Subject: Re: [RFC] high system time & lock contention running large mixed workload 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 Date: Tue, 1 Dec 2009 21:31:09 +0900 (JST) Sender: owner-linux-mm@kvack.org To: Andrea Arcangeli 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 List-ID: > 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, 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/ . Don't email: email@kvack.org