Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755154AbdCGKUr (ORCPT ); Tue, 7 Mar 2017 05:20:47 -0500 Received: from mx2.suse.de ([195.135.220.15]:53799 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754659AbdCGKUF (ORCPT ); Tue, 7 Mar 2017 05:20:05 -0500 Date: Tue, 7 Mar 2017 11:17:02 +0100 From: Michal Hocko To: Johannes Weiner Cc: Minchan Kim , Andrew Morton , Jia He , Mel Gorman , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@fb.com Subject: Re: [PATCH 1/9] mm: fix 100% CPU kswapd busyloop on unreclaimable nodes Message-ID: <20170307101702.GD28642@dhcp22.suse.cz> References: <20170228214007.5621-1-hannes@cmpxchg.org> <20170228214007.5621-2-hannes@cmpxchg.org> <20170303012609.GA3394@bbox> <20170303075954.GA31499@dhcp22.suse.cz> <20170306013740.GA8779@bbox> <20170306162410.GB2090@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170306162410.GB2090@cmpxchg.org> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2873 Lines: 90 On Mon 06-03-17 11:24:10, Johannes Weiner wrote: [...] > >From e126db716926ff353b35f3a6205bd5853e01877b Mon Sep 17 00:00:00 2001 > From: Johannes Weiner > Date: Mon, 6 Mar 2017 10:53:59 -0500 > Subject: [PATCH] mm: fix 100% CPU kswapd busyloop on unreclaimable nodes fix > > Check kswapd failure against the cumulative nr_reclaimed count, not > against the count from the lowest priority iteration. > > Suggested-by: Minchan Kim > Signed-off-by: Johannes Weiner > --- > mm/vmscan.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index ddcff8a11c1e..b834b2dd4e19 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -3179,9 +3179,9 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx) > count_vm_event(PAGEOUTRUN); > > do { > + unsigned long nr_reclaimed = sc.nr_reclaimed; > bool raise_priority = true; > > - sc.nr_reclaimed = 0; > sc.reclaim_idx = classzone_idx; > > /* > @@ -3271,7 +3271,8 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx) > * Raise priority if scanning rate is too low or there was no > * progress in reclaiming pages > */ > - if (raise_priority || !sc.nr_reclaimed) > + nr_reclaimed = sc.nr_reclaimed - nr_reclaimed; > + if (raise_priority || !nr_reclaimed) > sc.priority--; > } while (sc.priority >= 1); > I would rather not play with the sc state here. From a quick look at least /* * Fragmentation may mean that the system cannot be rebalanced for * high-order allocations. If twice the allocation size has been * reclaimed then recheck watermarks only at order-0 to prevent * excessive reclaim. Assume that a process requested a high-order * can direct reclaim/compact. */ if (sc->order && sc->nr_reclaimed >= compact_gap(sc->order)) sc->order = 0; does rely on the value. Wouldn't something like the following be safer? --- diff --git a/mm/vmscan.c b/mm/vmscan.c index c15b2e4c47ca..b731f24fed12 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -3183,6 +3183,7 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx) .may_unmap = 1, .may_swap = 1, }; + bool reclaimable = false; count_vm_event(PAGEOUTRUN); do { @@ -3274,6 +3275,9 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx) if (try_to_freeze() || kthread_should_stop()) break; + if (sc.nr_reclaimed) + reclaimable = true; + /* * Raise priority if scanning rate is too low or there was no * progress in reclaiming pages @@ -3282,7 +3286,7 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx) sc.priority--; } while (sc.priority >= 1); - if (!sc.nr_reclaimed) + if (!reclaimable) pgdat->kswapd_failures++; out: -- Michal Hocko SUSE Labs