From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <391631232.21419@ustc.edu.cn> Date: Sat, 6 Oct 2007 08:40:28 +0800 From: Fengguang Wu Subject: Re: [PATCH] remove throttle_vm_writeout() Message-ID: <20071006004028.GA7121@mail.ustc.edu.cn> References: <20071004164801.d8478727.akpm@linux-foundation.org> <20071004174851.b34a3220.akpm@linux-foundation.org> <1191572520.22357.42.camel@twins> <1191577623.22357.69.camel@twins> <1191581854.22357.85.camel@twins> <1191606600.6715.94.camel@heimdal.trondhjem.org> <1191609139.6210.4.camel@lappy> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1191609139.6210.4.camel@lappy> Sender: owner-linux-mm@kvack.org Return-Path: To: Peter Zijlstra Cc: Trond Myklebust , Miklos Szeredi , akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org List-ID: On Fri, Oct 05, 2007 at 08:32:19PM +0200, Peter Zijlstra wrote: > > On Fri, 2007-10-05 at 13:50 -0400, Trond Myklebust wrote: > > On Fri, 2007-10-05 at 12:57 +0200, Peter Zijlstra wrote: > > > In this patch I totally ignored unstable, but I'm not sure that's the > > > proper thing to do, I'd need to figure out what happens to an unstable > > > page when passed into pageout() - or if its passed to pageout at all. > > > > > > If unstable pages would be passed to pageout(), and it would properly > > > convert them to writeback and clean them, then there is nothing wrong. > > > > Why would we want to do that? That would be a hell of a lot of work > > (locking pages, setting flags, unlocking pages, ...) for absolutely no > > reason. > > > > Unstable writes are writes which have been sent to the server, but which > > haven't been written to disk on the server. A single RPC command is then > > sent (COMMIT) which basically tells the server to call fsync(). After > > that is successful, we can free up the pages, but we do that with no > > extra manipulation of the pages themselves: no page locks, just removal > > from the NFS private radix tree, and freeing up of the NFS private > > structures. > > > > We only need to touch the pages again in the unlikely case that the > > COMMIT fails because the server has rebooted. In this case we have to > > resend the writes, and so the pages are marked as dirty, so we can go > > through the whole writepages() rigmarole again... > > > > So, no. I don't see sending pages through pageout() as being at all > > helpful. > > Well, the thing is, we throttle pageout in throttle_vm_writeout(). As it > stand we can deadlock there because it just waits for the numbers to > drop, and unstable pages don't automagically dissapear. Only > write_inodes() - normally called from balance_dirty_pages() will call > COMMIT. I wonder whether if (!bdi_nr_writeback) break; or something like that could avoid the deadlock? > So my thought was that calling pageout() on an unstable page would do > the COMMIT - we're low on memory, otherwise we would not be paging, so > getting rid of unstable pages seems to make sense to me. I guess "many unstable pages" would be better if we are taking this way. -- 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