linux-kernel - Re: [patch] mm, thp: do not cause memcg oom for thp

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Date:   Tue, 20 Mar 2018 08:16:24 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     David Rientjes <rientjes@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Vlastimil Babka <vbabka@...e.cz>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [patch] mm, thp: do not cause memcg oom for thp

On Mon 19-03-18 14:10:05, David Rientjes wrote:
> Commit 2516035499b9 ("mm, thp: remove __GFP_NORETRY from khugepaged and
> madvised allocations") changed the page allocator to no longer detect thp
> allocations based on __GFP_NORETRY.
> 
> It did not, however, modify the mem cgroup try_charge() path to avoid oom
> kill for either khugepaged collapsing or thp faulting.  It is never
> expected to oom kill a process to allocate a hugepage for thp; reclaim is
> governed by the thp defrag mode and MADV_HUGEPAGE, but allocations (and
> charging) should fallback instead of oom killing processes.

For some reason I thought that the charging path simply bails out for
costly orders - effectively the same thing as for the global OOM killer.
But we do not. Is there any reason to not do that though? Why don't we
simply do


diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index d1a917b5b7b7..08accbcd1a18 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1493,7 +1493,7 @@ static void memcg_oom_recover(struct mem_cgroup *memcg)
 
 static void mem_cgroup_oom(struct mem_cgroup *memcg, gfp_t mask, int order)
 {
-	if (!current->memcg_may_oom)
+	if (!current->memcg_may_oom || order > PAGE_ALLOC_COSTLY_ORDER)
 		return;
 	/*
 	 * We are in the middle of the charge context here, so we
-- 
Michal Hocko
SUSE Labs