From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Pekka Enberg" Subject: Re: msync(2) bug(?), returns AOP_WRITEPAGE_ACTIVATE to userland Date: Mon, 22 Oct 2007 23:48:37 +0300 Message-ID: <84144f020710221348x297795c0qda61046ec69a7178@mail.gmail.com> References: <200710142232.l9EMW8kK029572@agora.fsl.cs.sunysb.edu> <84144f020710150447o94b1babo8b6e6a647828465f@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: "Erez Zadok" , "Ryan Finnie" , "Andrew Morton" , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, cjwatson@ubuntu.com, linux-mm@kvack.org, neilb@suse.de To: "Hugh Dickins" Return-path: Received: from rv-out-0910.google.com ([209.85.198.188]:17648 "EHLO rv-out-0910.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751205AbXJVUsi (ORCPT ); Mon, 22 Oct 2007 16:48:38 -0400 Received: by rv-out-0910.google.com with SMTP id k20so1298951rvb for ; Mon, 22 Oct 2007 13:48:37 -0700 (PDT) In-Reply-To: Content-Disposition: inline Sender: linux-fsdevel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org Hi Hugh, On Mon, 15 Oct 2007, Pekka Enberg wrote: > > I wonder whether _not setting_ BDI_CAP_NO_WRITEBACK implies that > > ->writepage() will never return AOP_WRITEPAGE_ACTIVATE for > > !wbc->for_reclaim case which would explain why we haven't hit this bug > > before. Hugh, Andrew? On 10/22/07, Hugh Dickins wrote: > Only ramdisk and shmem have been returning AOP_WRITEPAGE_ACTIVATE. > Both of those set BDI_CAP_NO_WRITEBACK. ramdisk never returned it > if !wbc->for_reclaim. I contend that shmem shouldn't either: it's > a special code to get the LRU rotation right, not useful elsewhere. > Though Documentation/filesystems/vfs.txt does imply wider use. > > I think this is where people use the phrase "go figure" ;) Heh. As far as I can tell, the implication of "wider use" was added by Neil in commit "341546f5ad6fce584531f744853a5807a140f2a9 Update some VFS documentation", so perhaps he might know? Neil? Pekka