linux-kernel - Re: [PATCH] oom: warn if we go OOM for higher order and compaction is disabled

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Message-ID: <20160830111632.GD23963@dhcp22.suse.cz>
Date:   Tue, 30 Aug 2016 13:16:32 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     David Rientjes <rientjes@...gle.com>,
        Johannes Weiner <hannes@...xchg.org>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] oom: warn if we go OOM for higher order and compaction
 is disabled

Ups, forgot to fold the fix up into the commit.
---
>From 32c000ea9beb18555ab368e4dd22bac1ca8370e8 Mon Sep 17 00:00:00 2001
From: Michal Hocko <mhocko@...e.com>
Date: Mon, 29 Aug 2016 17:08:20 +0200
Subject: [PATCH] oom: warn if we go OOM for higher order and compaction is
 disabled

Since the lumpy reclaim is gone there is no source of higher order pages
if CONFIG_COMPACTION=n except for the order-0 pages reclaim which is
unreliable for that purpose to say the least. Hitting an OOM for !costly
higher order requests is therefore all not that hard to imagine. We are
trying hard to not invoke OOM killer as much as possible but there is
simply no reliable way to detect whether more reclaim retries make sense.

Disabling COMPACTION is not widespread but it seems that some users
might have disable the feature without realizing full consequences
(mostly along with disabling THP because compaction used to be THP
mainly thing). This patch just adds a note if the OOM killer was
triggered by higher order request with compaction disabled. This will
help us identifying possible misconfiguration right from the oom report
which is easier than to always keep in mind that somebody might have
disabled COMPACTION without a good reason.

Signed-off-by: Michal Hocko <mhocko@...e.com>
---
 mm/oom_kill.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 10f686969fc4..0034baf35f0c 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -406,6 +406,8 @@ static void dump_header(struct oom_control *oc, struct task_struct *p)
 	pr_warn("%s invoked oom-killer: gfp_mask=%#x(%pGg), order=%d, oom_score_adj=%hd\n",
 		current->comm, oc->gfp_mask, &oc->gfp_mask, oc->order,
 		current->signal->oom_score_adj);
+	if (!IS_ENABLED(CONFIG_COMPACTION) && oc->order)
+		pr_warn("COMPACTION is disabled!!!\n");

 	cpuset_print_current_mems_allowed();
 	dump_stack();
-- 
2.8.1

-- 
Michal Hocko
SUSE Labs