From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from fgwmail6.fujitsu.co.jp ([192.51.44.36]) by bombadil.infradead.org with esmtp (Exim 4.69 #1 (Red Hat Linux)) id 1ND5xe-000809-H2 for linux-mtd@lists.infradead.org; Wed, 25 Nov 2009 00:42:27 +0000 Received: from m4.gw.fujitsu.co.jp ([10.0.50.74]) by fgwmail6.fujitsu.co.jp (Fujitsu Gateway) with ESMTP id nAP0gIeI001866 for (envelope-from kosaki.motohiro@jp.fujitsu.com); Wed, 25 Nov 2009 09:42:18 +0900 Received: from smail (m4 [127.0.0.1]) by outgoing.m4.gw.fujitsu.co.jp (Postfix) with ESMTP id 6CEA945DE70 for ; Wed, 25 Nov 2009 09:42:18 +0900 (JST) Received: from s4.gw.fujitsu.co.jp (s4.gw.fujitsu.co.jp [10.0.50.94]) by m4.gw.fujitsu.co.jp (Postfix) with ESMTP id 4CD1545DE60 for ; Wed, 25 Nov 2009 09:42:18 +0900 (JST) Received: from s4.gw.fujitsu.co.jp (localhost.localdomain [127.0.0.1]) by s4.gw.fujitsu.co.jp (Postfix) with ESMTP id 29F781DB8037 for ; Wed, 25 Nov 2009 09:42:18 +0900 (JST) Received: from m108.s.css.fujitsu.com (m108.s.css.fujitsu.com [10.249.87.108]) by s4.gw.fujitsu.co.jp (Postfix) with ESMTP id CD6E3E18003 for ; Wed, 25 Nov 2009 09:42:17 +0900 (JST) From: KOSAKI Motohiro To: Adrian Hunter 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) Cc: "Bityutskiy Artem \(Nokia-D/Helsinki\)" , David Woodhouse , LKML , linux-mm , "linux-mtd@lists.infradead.org" , kosaki.motohiro@jp.fujitsu.com, Andrew Morton List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , > 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?