linux-kernel - Re: [RFC 1/2] slub: Avoid trying to allocate memory on offline nodes

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Message-ID: <20180802091554.GE10808@dhcp22.suse.cz>
Date:   Thu, 2 Aug 2018 11:15:54 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Jeremy Linton <jeremy.linton@....com>
Cc:     linux-mm@...ck.org, cl@...ux.com, penberg@...nel.org,
        rientjes@...gle.com, iamjoonsoo.kim@....com,
        akpm@...ux-foundation.org, vbabka@...e.cz, Punit.Agrawal@....com,
        Lorenzo.Pieralisi@....com, linux-arm-kernel@...ts.infradead.org,
        bhelgaas@...gle.com, linux-kernel@...r.kernel.org
Subject: Re: [RFC 1/2] slub: Avoid trying to allocate memory on offline nodes

On Wed 01-08-18 15:04:17, Jeremy Linton wrote:
[...]
> @@ -2519,6 +2519,8 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
>  		if (unlikely(!node_match(page, searchnode))) {
>  			stat(s, ALLOC_NODE_MISMATCH);
>  			deactivate_slab(s, page, c->freelist, c);
> +			if (!node_online(searchnode))
> +				node = NUMA_NO_NODE;
>  			goto new_slab;

This is inherently racy. Numa node can get offline at any point after
you check it here. Making it race free would involve some sort of
locking and I am not really convinced this is a good idea.

>  		}
>  	}
> -- 
> 2.14.3
> 

-- 
Michal Hocko
SUSE Labs