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SubjectRe: [RFC 1/2] slub: Avoid trying to allocate memory on offline nodes
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Date
Hi,

On 08/02/2018 04:15 AM, Michal Hocko wrote:
> 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.

I spent some time looking/thinking about this, and i'm pretty sure its
not creating any new problems. But OTOH, I think the node_online() check
is probably a bit misleading as what we really want to assure is that
node<MAX_NUMNODES and that there is going to be a valid entry in
NODE_DATA() so we don't deference null.


>
>> }
>> }
>> --
>> 2.14.3
>>
>

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