From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail202.messagelabs.com (mail202.messagelabs.com [216.82.254.227]) by kanga.kvack.org (Postfix) with SMTP id 2AFA46B004A for ; Fri, 3 Sep 2010 22:05:14 -0400 (EDT) Date: Sat, 4 Sep 2010 10:04:53 +0800 From: Wu Fengguang Subject: Re: [RESEND PATCH v2] compaction: fix COMPACTPAGEFAILED counting Message-ID: <20100904020452.GA7788@localhost> References: <1283438087-11842-1-git-send-email-minchan.kim@gmail.com> <20100903170227.b2f18ba4.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100903170227.b2f18ba4.akpm@linux-foundation.org> Sender: owner-linux-mm@kvack.org To: Andrew Morton Cc: Minchan Kim , Christoph Lameter , Hugh Dickins , Andi Kleen , Mel Gorman , linux-mm , LKML List-ID: On Sat, Sep 04, 2010 at 08:02:27AM +0800, Andrew Morton wrote: > On Thu, 2 Sep 2010 23:34:47 +0900 > Minchan Kim wrote: > > > Now update_nr_listpages doesn't have a role. That's because > > lists passed is always empty just after calling migrate_pages. > > The migrate_pages cleans up page list which have failed to migrate > > before returning by aaa994b3. > > > > [PATCH] page migration: handle freeing of pages in migrate_pages() > > > > Do not leave pages on the lists passed to migrate_pages(). Seems that we will > > not need any postprocessing of pages. This will simplify the handling of > > pages by the callers of migrate_pages(). > > > > At that time, we thought we don't need any postprocessing of pages. > > But the situation is changed. The compaction need to know the number of > > failed to migrate for COMPACTPAGEFAILED stat > > > > This patch makes new rule for caller of migrate_pages to call putback_lru_pages. > > So caller need to clean up the lists so it has a chance to postprocess the pages. > > [suggested by Christoph Lameter] > > I'm having trouble predicting what the user-visible effects of this bug > might be. Just an inaccuracy in the COMPACTPAGEFAILED vm event? Right, it's an accounting fix. Before patch COMPACTPAGEFAILED will remain 0 regardless of how many migration failures. The patch does slightly add dependency for migrate_pages() to return error code properly. Before patch, migrate_pages() calls putback_lru_pages() regardless of the error code. After patch, the migrate_pages() callers will check its return value before calling putback_lru_pages(). In current code, the two conditions do seem to match: "some pages remained in the *from list" == "migrate_pages() returns an error code". Thanks, Fengguang -- 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