linux-kernel - Re: [patch] mm, oom: prevent soft lockup on memcg oom for UP systems

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Message-Id: <202003120012.02C0CEUB043533@www262.sakura.ne.jp>
Date:   Thu, 12 Mar 2020 09:12:14 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     David Rientjes <rientjes@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Michal Hocko <mhocko@...nel.org>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [patch] mm, oom: prevent soft lockup on memcg oom for UP systems

> On Thu, 12 Mar 2020, Tetsuo Handa wrote:
> > > If you have an alternate patch to try, we can test it.  But since this 
> > > cond_resched() is needed anyway, I'm not sure it will change the result.
> > 
> > schedule_timeout_killable(1) is an alternate patch to try; I don't think
> > that this cond_resched() is needed anyway.
> > 
> 
> You are suggesting schedule_timeout_killable(1) in shrink_node_memcgs()?
> 

Andrew Morton also mentioned whether cond_resched() in shrink_node_memcgs()
is enough. But like you mentioned,

David Rientjes wrote:
> On Tue, 10 Mar 2020, Andrew Morton wrote:
> 
> > > --- a/mm/vmscan.c
> > > +++ b/mm/vmscan.c
> > > @@ -2637,6 +2637,8 @@ static void shrink_node_memcgs(pg_data_t *pgdat, struct scan_control *sc)
> > >  		unsigned long reclaimed;
> > >  		unsigned long scanned;
> > >  
> > > +		cond_resched();
> > > +
> > >  		switch (mem_cgroup_protected(target_memcg, memcg)) {
> > >  		case MEMCG_PROT_MIN:
> > >  			/*
> > 
> > 
> > Obviously better, but this will still spin wheels until this tasks's
> > timeslice expires, and we might want to do something to help ensure
> > that the victim runs next (or soon)?
> > 
> 
> We used to have a schedule_timeout_killable(1) to address exactly that 
> scenario but it was removed in 4.19:
> 
> commit 9bfe5ded054b8e28a94c78580f233d6879a00146
> Author: Michal Hocko <mhocko@...e.com>
> Date:   Fri Aug 17 15:49:04 2018 -0700
> 
>     mm, oom: remove sleep from under oom_lock

you can try re-adding sleep outside of oom_lock:

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index d09776cd6e10..3aee7e0eca4e 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1576,6 +1576,7 @@ static bool mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask,
 	 */
 	ret = should_force_charge() || out_of_memory(&oc);
 	mutex_unlock(&oom_lock);
+	schedule_timeout_killable(1);
 	return ret;
 }
 
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 3c4eb750a199..e80158049651 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3797,7 +3797,6 @@ __alloc_pages_may_oom(gfp_t gfp_mask, unsigned int order,
 	 */
 	if (!mutex_trylock(&oom_lock)) {
 		*did_some_progress = 1;
-		schedule_timeout_uninterruptible(1);
 		return NULL;
 	}
 
@@ -4590,6 +4589,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
 
 	/* Retry as long as the OOM killer is making progress */
 	if (did_some_progress) {
+		schedule_timeout_uninterruptible(1);
 		no_progress_loops = 0;
 		goto retry;
 	}

By the way, will you share the reproducer (and how to use the reproducer) ?