From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail190.messagelabs.com (mail190.messagelabs.com [216.82.249.51]) by kanga.kvack.org (Postfix) with SMTP id 9A7536B01EF for ; Mon, 5 Apr 2010 22:58:48 -0400 (EDT) Received: from m1.gw.fujitsu.co.jp ([10.0.50.71]) by fgwmail5.fujitsu.co.jp (Fujitsu Gateway) with ESMTP id o362wjHm016658 for (envelope-from kosaki.motohiro@jp.fujitsu.com); Tue, 6 Apr 2010 11:58:45 +0900 Received: from smail (m1 [127.0.0.1]) by outgoing.m1.gw.fujitsu.co.jp (Postfix) with ESMTP id 1137145DE4E for ; Tue, 6 Apr 2010 11:58:45 +0900 (JST) Received: from s1.gw.fujitsu.co.jp (s1.gw.fujitsu.co.jp [10.0.50.91]) by m1.gw.fujitsu.co.jp (Postfix) with ESMTP id DAF1545DE4D for ; Tue, 6 Apr 2010 11:58:44 +0900 (JST) Received: from s1.gw.fujitsu.co.jp (localhost.localdomain [127.0.0.1]) by s1.gw.fujitsu.co.jp (Postfix) with ESMTP id BFBC91DB8045 for ; Tue, 6 Apr 2010 11:58:44 +0900 (JST) Received: from m106.s.css.fujitsu.com (m106.s.css.fujitsu.com [10.249.87.106]) by s1.gw.fujitsu.co.jp (Postfix) with ESMTP id 6CD291DB8040 for ; Tue, 6 Apr 2010 11:58:44 +0900 (JST) From: KOSAKI Motohiro Subject: Re: [PATCH]vmscan: handle underflow for get_scan_ratio In-Reply-To: <20100406023043.GA12420@localhost> References: <20100406105324.7E30.A69D9226@jp.fujitsu.com> <20100406023043.GA12420@localhost> Message-Id: <20100406115543.7E39.A69D9226@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Date: Tue, 6 Apr 2010 11:58:43 +0900 (JST) Sender: owner-linux-mm@kvack.org To: Wu Fengguang Cc: kosaki.motohiro@jp.fujitsu.com, "Li, Shaohua" , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , "akpm@linux-foundation.org" , Rik van Riel List-ID: > On Tue, Apr 06, 2010 at 10:06:19AM +0800, KOSAKI Motohiro wrote: > > > On Tue, Apr 06, 2010 at 09:25:36AM +0800, Li, Shaohua wrote: > > > > On Sun, Apr 04, 2010 at 10:19:06PM +0800, KOSAKI Motohiro wrote: > > > > > > On Fri, Apr 02, 2010 at 05:14:38PM +0800, KOSAKI Motohiro wrote: > > > > > > > > > > This patch makes a lot of sense than previous. however I think <1% anon ratio > > > > > > > > > > shouldn't happen anyway because file lru doesn't have reclaimable pages. > > > > > > > > > > <1% seems no good reclaim rate. > > > > > > > > > > > > > > > > > > Oops, the above mention is wrong. sorry. only 1 page is still too big. > > > > > > > > > because under streaming io workload, the number of scanning anon pages should > > > > > > > > > be zero. this is very strong requirement. if not, backup operation will makes > > > > > > > > > a lot of swapping out. > > > > > > > > Sounds there is no big impact for the workload which you mentioned with the patch. > > > > > > > > please see below descriptions. > > > > > > > > I updated the description of the patch as fengguang suggested. > > > > > > > > > > > > > > Umm.. sorry, no. > > > > > > > > > > > > > > "one fix but introduce another one bug" is not good deal. instead, > > > > > > > I'll revert the guilty commit at first as akpm mentioned. > > > > > > Even we revert the commit, the patch still has its benefit, as it increases > > > > > > calculation precision, right? > > > > > > > > > > no, you shouldn't ignore the regression case. > > > > > > > I don't think this is serious. In my calculation, there is only 1 page swapped out > > > > for 6G anonmous memory. 1 page should haven't any performance impact. > > > > > > 1 anon page scanned for every N file pages scanned? > > > > > > Is N a _huge_ enough ratio so that the anon list will be very light scanned? > > > > > > Rik: here is a little background. > > > > The problem is, the VM are couteniously discarding no longer used file > > cache. if we are scan extra anon 1 page, we will observe tons swap usage > > after few days. > > > > please don't only think benchmark. > > OK the days-of-streaming-io typically happen in file servers. Suppose > a file server with 16GB memory, 1GB of which is consumed by anonymous > pages, others are for page cache. > > Assume that the exact file:anon ratio computed by the get_scan_ratio() > algorithm is 1000:1. In that case percent[0]=0.1 and is rounded down > to 0, which keeps the anon pages in memory for the few days. > > Now with Shaohua's patch, nr[0] = (262144/4096)/1000 = 0.06 will also > be rounded down to 0. It only becomes >=1 when > - reclaim runs into trouble and priority goes low > - anon list goes huge > > So I guess Shaohua's patch still has reasonable "underflow" threshold :) Again, I didn't said his patch is no worth. I only said we don't have to ignore the downside. -- 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