Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754416Ab0GMI7a (ORCPT ); Tue, 13 Jul 2010 04:59:30 -0400 Received: from fxip-0047f.externet.hu ([88.209.222.127]:60714 "EHLO pomaz-ex.szeredi.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753707Ab0GMI72 (ORCPT ); Tue, 13 Jul 2010 04:59:28 -0400 To: Andrew Morton CC: fengguang.wu@intel.com, hch@infradead.org, richard@rsk.demon.co.uk, david@fromorbit.com, jack@suse.cz, a.p.zijlstra@chello.nl, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, miklos@szeredi.hu In-reply-to: <20100712145206.9808b411.akpm@linux-foundation.org> (message from Andrew Morton on Mon, 12 Jul 2010 14:52:06 -0700) Subject: Re: [PATCH 1/6] writeback: take account of NR_WRITEBACK_TEMP in balance_dirty_pages() References: <20100711020656.340075560@intel.com> <20100711021748.594522648@intel.com> <20100712145206.9808b411.akpm@linux-foundation.org> Message-Id: From: Miklos Szeredi Date: Tue, 13 Jul 2010 10:58:47 +0200 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2485 Lines: 63 On Mon, 12 Jul 2010, Andrew Morton wrote: > On Sun, 11 Jul 2010 10:06:57 +0800 > Wu Fengguang wrote: > > > > > Signed-off-by: Richard Kennedy > > Signed-off-by: Wu Fengguang > > --- > > mm/page-writeback.c | 7 ++++--- > > 1 file changed, 4 insertions(+), 3 deletions(-) > > > > --- linux-next.orig/mm/page-writeback.c 2010-07-11 08:41:37.000000000 +0800 > > +++ linux-next/mm/page-writeback.c 2010-07-11 08:42:14.000000000 +0800 > > @@ -503,11 +503,12 @@ static void balance_dirty_pages(struct a > > }; > > > > get_dirty_limits(&background_thresh, &dirty_thresh, > > - &bdi_thresh, bdi); > > + &bdi_thresh, bdi); > > > > nr_reclaimable = global_page_state(NR_FILE_DIRTY) + > > - global_page_state(NR_UNSTABLE_NFS); > > - nr_writeback = global_page_state(NR_WRITEBACK); > > + global_page_state(NR_UNSTABLE_NFS); > > + nr_writeback = global_page_state(NR_WRITEBACK) + > > + global_page_state(NR_WRITEBACK_TEMP); > > > > bdi_nr_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE); > > bdi_nr_writeback = bdi_stat(bdi, BDI_WRITEBACK); > > > > hm, OK. Hm, hm. I'm not sure this is right. The VM has absolutely no control over NR_WRITEBACK_TEMP pages, they may clear quickly or may not make any progress. So it's usually wrong to make a decision based on NR_WRITEBACK_TEMP for an unrelated device. Using it in throttle_vm_writeout() would actually be deadlocky, since the userspace filesystem will probably depend on memory allocations to complete the writeout. The only place where we should be taking NR_WRITEBACK_TEMP into account is calculating the remaining memory that can be devided between dirtyers, and that's (clip_bdi_dirty_limit) where it is already used. > I wonder whether we could/should have unified NR_WRITEBACK_TEMP and > NR_UNSTABLE_NFS. Their "meanings" aren't quite the same, but perhaps > some "treat page as dirty because the fs is futzing with it" thing. AFAICS NR_UNSTABLE_NFS is something akin to NR_DIRTY, only on the server side. So nfs can very much do something about making NR_UNSTABLE_NFS go away, while there's nothing that can be done about NR_WRITEBACK_TEMP. Thanks, Miklos -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/