From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail137.messagelabs.com (mail137.messagelabs.com [216.82.249.19]) by kanga.kvack.org (Postfix) with SMTP id D62BB6B0044 for ; Tue, 24 Nov 2009 19:42:20 -0500 (EST) Received: from m5.gw.fujitsu.co.jp ([10.0.50.75]) by fgwmail6.fujitsu.co.jp (Fujitsu Gateway) with ESMTP id nAP0gIu1001855 for (envelope-from kosaki.motohiro@jp.fujitsu.com); Wed, 25 Nov 2009 09:42:18 +0900 Received: from smail (m5 [127.0.0.1]) by outgoing.m5.gw.fujitsu.co.jp (Postfix) with ESMTP id D1F7245DE51 for ; Wed, 25 Nov 2009 09:42:17 +0900 (JST) Received: from s5.gw.fujitsu.co.jp (s5.gw.fujitsu.co.jp [10.0.50.95]) by m5.gw.fujitsu.co.jp (Postfix) with ESMTP id AC2C845DE4F for ; Wed, 25 Nov 2009 09:42:17 +0900 (JST) Received: from s5.gw.fujitsu.co.jp (localhost.localdomain [127.0.0.1]) by s5.gw.fujitsu.co.jp (Postfix) with ESMTP id 989DEE1800B for ; Wed, 25 Nov 2009 09:42:17 +0900 (JST) Received: from m108.s.css.fujitsu.com (m108.s.css.fujitsu.com [10.249.87.108]) by s5.gw.fujitsu.co.jp (Postfix) with ESMTP id 482EF1DB8038 for ; Wed, 25 Nov 2009 09:42:17 +0900 (JST) From: KOSAKI Motohiro Subject: Re: [PATCH 4/7] nandsim: Don't use PF_MEMALLOC 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 Date: Wed, 25 Nov 2009 09:42:16 +0900 (JST) Sender: owner-linux-mm@kvack.org To: Adrian Hunter Cc: kosaki.motohiro@jp.fujitsu.com, "Bityutskiy Artem (Nokia-D/Helsinki)" , LKML , linux-mm , Andrew Morton , David Woodhouse , "linux-mtd@lists.infradead.org" List-ID: > 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? -- 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