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

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Date:   Thu, 2 Aug 2018 14:23:34 +0000
From:   Christopher Lameter <cl@...ux.com>
To:     Jeremy Linton <jeremy.linton@....com>
cc:     linux-mm@...ck.org, penberg@...nel.org, rientjes@...gle.com,
        iamjoonsoo.kim@....com, akpm@...ux-foundation.org, mhocko@...e.com,
        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, 1 Aug 2018, Jeremy Linton wrote:

> diff --git a/mm/slub.c b/mm/slub.c
> index 51258eff4178..e03719bac1e2 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -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;
>  		}
>  	}
>

Would it not be better to implement this check in the page allocator?
There is also the issue of how to fallback to the nearest node.

NUMA_NO_NODE should fallback to the current memory allocation policy but
it seems by inserting it here you would end up just with the default node
for the processor.