From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933656AbZKYAmO (ORCPT ); Tue, 24 Nov 2009 19:42:14 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S933355AbZKYAmN (ORCPT ); Tue, 24 Nov 2009 19:42:13 -0500 Received: from fgwmail7.fujitsu.co.jp ([192.51.44.37]:33368 "EHLO fgwmail7.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933178AbZKYAmN (ORCPT ); Tue, 24 Nov 2009 19:42:13 -0500 X-SecurityPolicyCheck-FJ: OK by FujitsuOutboundMailChecker v1.3.1 From: KOSAKI Motohiro To: Adrian Hunter Subject: Re: [PATCH 4/7] nandsim: Don't use PF_MEMALLOC Cc: kosaki.motohiro@jp.fujitsu.com, "Bityutskiy Artem (Nokia-D/Helsinki)" , LKML , linux-mm , Andrew Morton , David Woodhouse , "linux-mtd@lists.infradead.org" In-Reply-To: <4B0BC9E3.6070504@nokia.com> References: <20091124194532.AFC2.A69D9226@jp.fujitsu.com> <4B0BC9E3.6070504@nokia.com> Message-Id: <20091125084630.AFC5.A69D9226@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit X-Mailer: Becky! ver. 2.50.07 [ja] Date: Wed, 25 Nov 2009 09:42:16 +0900 (JST) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > ext KOSAKI Motohiro wrote: > > Hi > > > > Thank you for this useful comments. > > > >>> I vaguely remember Adrian (CCed) did this on purpose. This is for the > >>> case when nandsim emulates NAND flash on top of a file. So there are 2 > >>> file-systems involved: one sits on top of nandsim (e.g. UBIFS) and the > >>> other owns the file which nandsim uses (e.g., ext3). > >>> > >>> And I really cannot remember off the top of my head why he needed > >>> PF_MEMALLOC, but I think Adrian wanted to prevent the direct reclaim > >>> path to re-enter, say UBIFS, and cause deadlock. But I'd thing that all > >>> the allocations in vfs_read()/vfs_write() should be GFP_NOFS, so that > >>> should not be a probelm? > >>> > >> Yes it needs PF_MEMALLOC to prevent deadlock because there can be a > >> file system on top of nandsim which, in this case, is on top of another > >> file system. > >> > >> I do not see how mempools will help here. > >> > >> Please offer an alternative solution. > > > > I have few questions. > > > > Can you please explain more detail? Another stackable filesystam > > (e.g. ecryptfs) don't have such problem. Why nandsim have its issue? > > What lock cause deadlock? > > The file systems are not stacked. One is over nandsim, which nandsim > does not know about because it is just a lowly NAND device, and, with > the file cache option, one file system below to provide the file cache. > > The deadlock is the kernel writing out dirty pages to the top file system > which writes to nandsim which writes to the bottom file system which > allocates memory which causes dirty pages to be written out to the top > file system, which tries to write to nandsim => deadlock. You mean you want to prevent pageout() instead reclaim itself? Dropping filecache seems don't make recursive call, right?