From: Hisashi Hifumi Subject: Re: [PATCH] vmscan: set try_to_release_page's gfp_mask to 0 Date: Wed, 13 Aug 2008 15:24:40 +0900 Message-ID: <6.0.0.20.2.20080813150454.03b13e30@172.19.0.2> References: <6.0.0.20.2.20080813111835.03d345b0@172.19.0.2> <20080812202127.b88e8250.akpm@linux-foundation.org> 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, Mingming Cao To: Andrew Morton Return-path: In-Reply-To: <20080812202127.b88e8250.akpm@linux-foundation.org> References: <6.0.0.20.2.20080813111835.03d345b0@172.19.0.2> <20080812202127.b88e8250.akpm@linux-foundation.org> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org 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. > >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? Currently, we are discussing about direct-io -EIO problem because the patch ("jbd: fix race between free buffer and commit transaction") was not enough to fix the issue. The ML subject of this discussion is "[PATCH] jbd jbd2: fix diowritereturningEIOwhentry_to_release_page fails".