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Subject: Re: [PATCH] mm, oom: consider present pages for the node size
To:     Michal Hocko <mhocko@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     David Rientjes <rientjes@google.com>, linux-mm@kvack.org,
        LKML <linux-kernel@vger.kernel.org>,
        Michal Hocko <mhocko@suse.com>
References: <20190829163443.899-1-mhocko@kernel.org>
From:   David Hildenbrand <david@redhat.com>
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Organization: Red Hat GmbH
Message-ID: <31ea8cf0-0552-52cd-a206-ef41fb018d44@redhat.com>
Date:   Thu, 29 Aug 2019 19:00:41 +0200
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On 29.08.19 18:34, Michal Hocko wrote:
> From: Michal Hocko <mhocko@suse.com>
> 
> constrained_alloc calculates the size of the oom domain by using
> node_spanned_pages which is incorrect because this is the full range of
> the physical memory range that the numa node occupies rather than the
> memory that backs that range which is represented by node_present_pages.
> 
> Sparsely populated nodes (e.g. after memory hot remove or simply sparse
> due to memory layout) can have really a large difference between the
> two. This shouldn't really cause any real user observable problems
> because the oom calculates a ratio against totalpages and used memory
> cannot exceed present pages but it is confusing and wrong from code
> point of view.
> 
> Noticed-by: David Hildenbrand <david@redhat.com>
> Signed-off-by: Michal Hocko <mhocko@suse.com>
> ---
>  mm/oom_kill.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index eda2e2a0bdc6..16af3da97d08 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -287,7 +287,7 @@ static enum oom_constraint constrained_alloc(struct oom_control *oc)
>  	    !nodes_subset(node_states[N_MEMORY], *oc->nodemask)) {
>  		oc->totalpages = total_swap_pages;
>  		for_each_node_mask(nid, *oc->nodemask)
> -			oc->totalpages += node_spanned_pages(nid);
> +			oc->totalpages += node_present_pages(nid);
>  		return CONSTRAINT_MEMORY_POLICY;
>  	}
>  
> @@ -300,7 +300,7 @@ static enum oom_constraint constrained_alloc(struct oom_control *oc)
>  	if (cpuset_limited) {
>  		oc->totalpages = total_swap_pages;
>  		for_each_node_mask(nid, cpuset_current_mems_allowed)
> -			oc->totalpages += node_spanned_pages(nid);
> +			oc->totalpages += node_present_pages(nid);
>  		return CONSTRAINT_CPUSET;
>  	}
>  	return CONSTRAINT_NONE;>

Thanks!

Reviewed-by: David Hildenbrand <david@redhat.com>

-- 

Thanks,

David / dhildenb