linux-kernel - Re: [PATCH 1/2] mm, oom: do not rely on TIF

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Message-Id: <201708031703.HGC35950.LSJFOHQFtFMOVO@I-love.SAKURA.ne.jp>
Date:   Thu, 3 Aug 2017 17:03:20 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     mhocko@...nel.org
Cc:     akpm@...ux-foundation.org, rientjes@...gle.com, hannes@...xchg.org,
        guro@...com, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] mm, oom: do not rely on TIF_MEMDIE for memory reserves access

Michal Hocko wrote:
> Look, I really appreciate your sentiment for for nommu platform but with
> an absolute lack of _any_ oom reports on that platform that I am aware
> of nor any reports about lockups during oom I am less than thrilled to
> add a code to fix a problem which even might not exist. Nommu is usually
> very special with a very specific workload running (e.g. no overcommit)
> so I strongly suspect that any OOM theories are highly academic.

If you believe that there is really no oom report, get rid of the OOM
killer completely.

> 
> All I do care about is to not regress nommu as much as possible. So can
> we get back to the proposed patch and updates I have done to address
> your review feedback please?

No unless we get rid of the OOM killer if CONFIG_MMU=n.

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 170db4d..e931969 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3312,7 +3312,8 @@ void warn_alloc(gfp_t gfp_mask, nodemask_t *nodemask, const char *fmt, ...)
 		goto out;
 
 	/* Exhausted what can be done so it's blamo time */
-	if (out_of_memory(&oc) || WARN_ON_ONCE(gfp_mask & __GFP_NOFAIL)) {
+	if ((IS_ENABLED(CONFIG_MMU) && out_of_memory(&oc)) ||
+		WARN_ON_ONCE(gfp_mask & __GFP_NOFAIL)) {
 		*did_some_progress = 1;
 
 		/*