From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752426Ab1I1Cpg (ORCPT ); Tue, 27 Sep 2011 22:45:36 -0400 Received: from fgwmail6.fujitsu.co.jp ([192.51.44.36]:59421 "EHLO fgwmail6.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751558Ab1I1Cpf (ORCPT ); Tue, 27 Sep 2011 22:45:35 -0400 X-SecurityPolicyCheck-FJ: OK by FujitsuOutboundMailChecker v1.3.1 Message-ID: <4E828AFC.7070405@jp.fujitsu.com> Date: Wed, 28 Sep 2011 11:48:28 +0900 From: KOSAKI Motohiro User-Agent: Mozilla/5.0 (Windows NT 5.1; rv:6.0.2) Gecko/20110902 Thunderbird/6.0.2 MIME-Version: 1.0 To: minchan.kim@gmail.com CC: akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, jweiner@redhat.com, mel@csn.ul.ie, riel@redhat.com, lee.schermerhorn@hp.com Subject: Re: [PATCH] vmscan: add barrier to prevent evictable page in unevictable list References: <1317174330-2677-1-git-send-email-minchan.kim@gmail.com> <4E8284C6.1050900@jp.fujitsu.com> <20110928022510.GB12100@barrios-desktop> In-Reply-To: <20110928022510.GB12100@barrios-desktop> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org (2011/09/28 11:25), Minchan Kim wrote: > On Wed, Sep 28, 2011 at 11:21:58AM +0900, KOSAKI Motohiro wrote: >> (2011/09/28 10:45), Minchan Kim wrote: >>> When racing between putback_lru_page and shmem_unlock happens, >>> progrom execution order is as follows, but clear_bit in processor #1 >>> could be reordered right before spin_unlock of processor #1. >>> Then, the page would be stranded on the unevictable list. >>> >>> spin_lock >>> SetPageLRU >>> spin_unlock >>> clear_bit(AS_UNEVICTABLE) >>> spin_lock >>> if PageLRU() >>> if !test_bit(AS_UNEVICTABLE) >>> move evictable list >>> smp_mb >>> if !test_bit(AS_UNEVICTABLE) >>> move evictable list >>> spin_unlock >>> >>> But, pagevec_lookup in scan_mapping_unevictable_pages has rcu_read_[un]lock so >>> it could protect reordering before reaching test_bit(AS_UNEVICTABLE) on processor #1 >>> so this problem never happens. But it's a unexpected side effect and we should >>> solve this problem properly. >> >> Do we still need this after Hannes removes scan_mapping_unevictable_pages? > > Hi KOSAKI, > > What Hannes removes is scan_zone_unevictable_pages not scan_mapping_unevictable_pages. > Oops, you are right.