David Rientjes <rientjes@xxxxxxxxxx> writes:
> On Mon, 24 Nov 2014, Kirill A. Shutemov wrote:
>
>> > This make sure that we try to allocate hugepages from local node. If
>> > we can't we fallback to small page allocation based on
>> > mempolicy. This is based on the observation that allocating pages
>> > on local node is more beneficial that allocating hugepages on remote node.
>>
>> Local node on allocation is not necessary local node for use.
>> If policy says to use a specific node[s], we should follow.
>>
>
> True, and the interaction between thp and mempolicies is fragile: if a
> process has a MPOL_BIND mempolicy over a set of nodes, that does not
> necessarily mean that we want to allocate thp remotely if it will always
> be accessed remotely. It's simple to benchmark and show that remote
> access latency of a hugepage can exceed that of local pages. MPOL_BIND
> itself is a policy of exclusion, not inclusion, and it's difficult to
> define when local pages and its cost of allocation is better than remote
> thp.
>
> For MPOL_BIND, if the local node is allowed then thp should be forced from
> that node, if the local node is disallowed then allocate from any node in
> the nodemask. For MPOL_INTERLEAVE, I think we should only allocate thp
> from the next node in order, otherwise fail the allocation and fallback to
> small pages. Is this what you meant as well?
>
Something like below
struct page *alloc_hugepage_vma(gfp_t gfp, struct vm_area_struct *vma,
unsigned long addr, int order)
{
struct page *page;
nodemask_t *nmask;
struct mempolicy *pol;
int node = numa_node_id();
unsigned int cpuset_mems_cookie;
retry_cpuset:
pol = get_vma_policy(vma, addr);
cpuset_mems_cookie = read_mems_allowed_begin();
if (unlikely(pol->mode == MPOL_INTERLEAVE)) {
unsigned nid;
nid = interleave_nid(pol, vma, addr, PAGE_SHIFT + order);
mpol_cond_put(pol);
page = alloc_page_interleave(gfp, order, nid);
if (unlikely(!page &&
read_mems_allowed_retry(cpuset_mems_cookie)))
goto retry_cpuset;
return page;
}
nmask = policy_nodemask(gfp, pol);
if (!nmask || node_isset(node, *nmask)) {
mpol_cond_put(pol);
page = alloc_hugepage_exact_node(node, gfp, order);
if (unlikely(!page &&
read_mems_allowed_retry(cpuset_mems_cookie)))
goto retry_cpuset;
return page;
}
/*
* if current node is not part of node mask, try
* the allocation from any node, and we can do retry
* in that case.
*/
page = __alloc_pages_nodemask(gfp, order,
policy_zonelist(gfp, pol, node),
nmask);
mpol_cond_put(pol);
if (unlikely(!page && read_mems_allowed_retry(cpuset_mems_cookie)))
goto retry_cpuset;
return page;
}
-aneesh
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