From: Andrew Morton Subject: Re: [PATCH] vmscan: set try_to_release_page's gfp_mask to 0 Date: Wed, 15 Oct 2008 15:36:41 -0700 Message-ID: <20081015153641.afcc94e5.akpm@linux-foundation.org> References: <6.0.0.20.2.20080813111835.03d345b0@172.19.0.2> <20080812202127.b88e8250.akpm@linux-foundation.org> <6.0.0.20.2.20080813150454.03b13e30@172.19.0.2> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-ext4@vger.kernel.org, cmm@us.ibm.com To: Hisashi Hifumi Return-path: Received: from smtp1.linux-foundation.org ([140.211.169.13]:52440 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753179AbYJOWgx (ORCPT ); Wed, 15 Oct 2008 18:36:53 -0400 In-Reply-To: <6.0.0.20.2.20080813150454.03b13e30@172.19.0.2> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Wed, 13 Aug 2008 15:24:40 +0900 Hisashi Hifumi wrote: > At 12:21 08/08/13, Andrew Morton wrote: > >On Wed, 13 Aug 2008 11:21:16 +0900 Hisashi Hifumi > > wrote: > > > >> Hi. > >> > >> shrink_page_list passes gfp_mask to try_to_release_page. > >> When shrink_page_list is called from kswapd or buddy system, gfp_mask is set > >> and (gfp_mask & __GFP_WAIT) and (gfp_mask & __GFP_FS) check is positive. > >> releasepage of jbd/jbd2(ext3/4, ocfs2) and XFS use this parameter. > >> If try_to_free_page fails due to bh busy in jbd/jbd2, jbd/jbd2 lets a > >thread wait for > >> committing transaction. I think this has big performance impacts for vmscan. > >> So I modified shrink_page_list not to pass gfp_mask to try_to_release_page > >> in ordered to improve vmscan performance. > >> > >> Thanks. > >> > >> Signed-off-by: Hisashi Hifumi > >> > >> diff -Nrup linux-2.6.27-rc2.org/mm/vmscan.c linux-2.6.27-rc2.vmscan/mm/vmscan.c > >> --- linux-2.6.27-rc2.org/mm/vmscan.c 2008-08-11 14:33:24.000000000 +0900 > >> +++ linux-2.6.27-rc2.vmscan/mm/vmscan.c 2008-08-12 18:57:05.000000000 +0900 > >> @@ -614,7 +614,7 @@ static unsigned long shrink_page_list(st > >> * Otherwise, leave the page on the LRU so it is swappable. > >> */ > >> if (PagePrivate(page)) { > >> - if (!try_to_release_page(page, sc->gfp_mask)) > >> + if (!try_to_release_page(page, 0)) > >> goto activate_locked; > >> if (!mapping && page_count(page) == 1) { > >> unlock_page(page); > > > >I think the change makes sense. > > > >Has this change been shown to improve any workloads? If so, please > >provide full information for the changelog. If not, please mention > >this and explain why benefits were not demonstrable. This information > >should _always_ be present in a "performance" patch's changelog! > > Sorry, I do not have performance number yet. I'll try this. > This patch remains in a stalled state... And then there's this: : Probably a better fix would be to explicitly tell : journal_try_to_free_buffers() when it need to block on journal commit, : rather than (mis)interpreting the gfp_t in this fashion. I assume the : only caller who really cares is direct-io. That would be quite a bit : of churn, and the asynchronous behaviour perhaps makes sense _anyway_ : when called from page reclaim. : : otoh, there is a risk that this change will cause page reclaim to sit : there burning huge amounts of CPU time and not achieving anything, : because all it is doing is scanning over busy pages. In that case, : blocking behind a commit which would make those pages reclaimable is : correct behaviour. But given that the offending code in : journal_try_to_free_buffers() has only been there for a few weeks, I : guess this isn't a concern. : : : Really, I think what this patch tells us is that 3f31fddf ("jbd: fix : race between free buffer and commit transaction") was an unpleasant : hack which had undesirable and unexpected side-effects. I think - that : depends upon your as-yet-undisclosed testing results? : : Perhaps we should revert 3f31fddf and have another think about how to : fix the direct-io -EIO problem. One option would be to hold our noses : and add a new gfp_t flag for this specific purpose? :