From patchwork Wed Oct 9 03:21:13 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Dave Chinner X-Patchwork-Id: 11180393 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id B09F818B7 for ; Wed, 9 Oct 2019 03:21:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9B55021871 for ; Wed, 9 Oct 2019 03:21:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730650AbfJIDVy (ORCPT ); Tue, 8 Oct 2019 23:21:54 -0400 Received: from mail105.syd.optusnet.com.au ([211.29.132.249]:58007 "EHLO mail105.syd.optusnet.com.au" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730496AbfJIDVf (ORCPT ); Tue, 8 Oct 2019 23:21:35 -0400 Received: from dread.disaster.area (pa49-181-226-196.pa.nsw.optusnet.com.au [49.181.226.196]) by mail105.syd.optusnet.com.au (Postfix) with ESMTPS id 56B213632DC; Wed, 9 Oct 2019 14:21:28 +1100 (AEDT) Received: from discord.disaster.area ([192.168.253.110]) by dread.disaster.area with esmtp (Exim 4.92.2) (envelope-from ) id 1iI2XX-0006Bj-61; Wed, 09 Oct 2019 14:21:27 +1100 Received: from dave by discord.disaster.area with local (Exim 4.92) (envelope-from ) id 1iI2XX-00039c-47; Wed, 09 Oct 2019 14:21:27 +1100 From: Dave Chinner To: linux-xfs@vger.kernel.org Cc: linux-mm@kvack.org, linux-fsdevel@vger.kernel.org Subject: [PATCH 15/26] mm: kswapd backoff for shrinkers Date: Wed, 9 Oct 2019 14:21:13 +1100 Message-Id: <20191009032124.10541-16-david@fromorbit.com> X-Mailer: git-send-email 2.23.0.rc1 In-Reply-To: <20191009032124.10541-1-david@fromorbit.com> References: <20191009032124.10541-1-david@fromorbit.com> MIME-Version: 1.0 X-Optus-CM-Score: 0 X-Optus-CM-Analysis: v=2.2 cv=FNpr/6gs c=1 sm=1 tr=0 a=dRuLqZ1tmBNts2YiI0zFQg==:117 a=dRuLqZ1tmBNts2YiI0zFQg==:17 a=jpOVt7BSZ2e4Z31A5e1TngXxSK0=:19 a=XobE76Q3jBoA:10 a=20KFwNOVAAAA:8 a=NNMOctoXzqbiiAOzY8AA:9 Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org From: Dave Chinner When kswapd reaches the end of the page LRU and starts hitting dirty pages, the logic in shrink_node() allows it to back off and wait for IO to complete, thereby preventing kswapd from scanning excessively and driving the system into swap thrashing and OOM conditions. When we have inode cache heavy workloads on XFS, we have exactly the same problem with reclaim inodes. The non-blocking kswapd reclaim will keep putting pressure onto the inode cache which is unable to make progress. When the system gets to the point where there is no pages in the LRU to free, there is no swap left and there are no clean inodes that can be freed, it will OOM. This has a specific signature in OOM: [ 110.841987] Mem-Info: [ 110.842816] active_anon:241 inactive_anon:82 isolated_anon:1 active_file:168 inactive_file:143 isolated_file:0 unevictable:2621523 dirty:1 writeback:8 unstable:0 slab_reclaimable:564445 slab_unreclaimable:420046 mapped:1042 shmem:11 pagetables:6509 bounce:0 free:77626 free_pcp:2 free_cma:0 In this case, we have about 500-600 pages left in teh LRUs, but we have ~565000 reclaimable slab pages still available for reclaim. Unfortunately, they are mostly dirty inodes, and so we really need to be able to throttle kswapd when shrinker progress is limited due to reaching the dirty end of the LRU... So, add a flag into the reclaim_state so if the shrinker decides it needs kswapd to back off and wait for a while (for whatever reason) it can do so. Signed-off-by: Dave Chinner --- include/linux/swap.h | 1 + mm/vmscan.c | 10 +++++++++- 2 files changed, 10 insertions(+), 1 deletion(-) diff --git a/include/linux/swap.h b/include/linux/swap.h index da0913e14bb9..76fc28f0e483 100644 --- a/include/linux/swap.h +++ b/include/linux/swap.h @@ -133,6 +133,7 @@ struct reclaim_state { unsigned long reclaimed_pages; /* pages freed by shrinkers */ unsigned long scanned_objects; /* quantity of work done */ unsigned long deferred_objects; /* work that wasn't done */ + bool need_backoff; /* tell kswapd to slow down */ }; /* diff --git a/mm/vmscan.c b/mm/vmscan.c index fe8e8508f98d..c56a9ac6d042 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -2951,8 +2951,16 @@ static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc) * implies that pages are cycling through the LRU * faster than they are written so also forcibly stall. */ - if (sc->nr.immediate) + if (sc->nr.immediate) { congestion_wait(BLK_RW_ASYNC, HZ/10); + } else if (reclaim_state && reclaim_state->need_backoff) { + /* + * Ditto, but it's a slab cache that is cycling + * through the LRU faster than they are written + */ + congestion_wait(BLK_RW_ASYNC, HZ/10); + reclaim_state->need_backoff = false; + } } /*