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 59C5C6B01EE for ; Sun, 11 Apr 2010 22:01:59 -0400 (EDT) Date: Mon, 12 Apr 2010 09:57:39 +0800 From: Shaohua Li Subject: Re: [PATCH]vmscan: handle underflow for get_scan_ratio Message-ID: <20100412015739.GA14988@sli10-desk.sh.intel.com> References: <20100331045348.GA3396@sli10-desk.sh.intel.com> <20100331142708.039E.A69D9226@jp.fujitsu.com> <20100331145030.03A1.A69D9226@jp.fujitsu.com> <20100402065052.GA28027@sli10-desk.sh.intel.com> <20100406050325.GA17797@localhost> <20100409065104.GA21480@sli10-desk.sh.intel.com> <20100409142057.be0ce5af.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100409142057.be0ce5af.akpm@linux-foundation.org> Sender: owner-linux-mm@kvack.org To: Andrew Morton Cc: "Wu, Fengguang" , KOSAKI Motohiro , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , "riel@redhat.com" List-ID: On Sat, Apr 10, 2010 at 05:20:57AM +0800, Andrew Morton wrote: > On Fri, 9 Apr 2010 14:51:04 +0800 > Shaohua Li wrote: > > > get_scan_ratio() calculates percentage and if the percentage is < 1%, it will > > round percentage down to 0% and cause we completely ignore scanning anon/file > > pages to reclaim memory even the total anon/file pages are very big. > > > > To avoid underflow, we don't use percentage, instead we directly calculate > > how many pages should be scaned. In this way, we should get several scanned pages > > for < 1% percent. > > > > This has some benefits: > > 1. increase our calculation precision > > 2. making our scan more smoothly. Without this, if percent[x] is underflow, > > shrink_zone() doesn't scan any pages and suddenly it scans all pages when priority > > is zero. With this, even priority isn't zero, shrink_zone() gets chance to scan > > some pages. > > > > Note, this patch doesn't really change logics, but just increase precision. For > > system with a lot of memory, this might slightly changes behavior. For example, > > in a sequential file read workload, without the patch, we don't swap any anon > > pages. With it, if anon memory size is bigger than 16G, we will see one anon page > > swapped. The 16G is calculated as PAGE_SIZE * priority(4096) * (fp/ap). fp/ap > > is assumed to be 1024 which is common in this workload. So the impact sounds not > > a big deal. > > I grabbed this. > > Did we decide that this needed to be backported into 2.6.33.x? If so, > some words explaining the reasoning would be needed. > > Come to that, it's not obvious that we need this in 2.6.34 either. Not needed. > is the user-visible impact here? Should be very small I think. Thanks, Shaohua -- 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