From mboxrd@z Thu Jan 1 00:00:00 1970 Subject: Re: [PATCH] remove throttle_vm_writeout() From: Peter Zijlstra In-Reply-To: <1191606600.6715.94.camel@heimdal.trondhjem.org> References: <20071004145640.18ced770.akpm@linux-foundation.org> <20071004160941.e0c0c7e5.akpm@linux-foundation.org> <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> Content-Type: text/plain Date: Fri, 05 Oct 2007 20:32:19 +0200 Message-Id: <1191609139.6210.4.camel@lappy> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Trond Myklebust Cc: Miklos Szeredi , akpm@linux-foundation.org, wfg@mail.ustc.edu.cn, linux-mm@kvack.org, linux-kernel@vger.kernel.org List-ID: 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. 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. -- 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