Messages in this thread | | | Date | Wed, 25 Feb 2015 11:52:28 +0100 | From | Vlastimil Babka <> | Subject | Re: [patch v2 for-4.0] mm, thp: really limit transparent hugepage allocation to local node |
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On 02/25/2015 12:24 AM, David Rientjes wrote: > From: Greg Thelen <gthelen@google.com> > > Commit 077fcf116c8c ("mm/thp: allocate transparent hugepages on local > node") restructured alloc_hugepage_vma() with the intent of only > allocating transparent hugepages locally when there was not an effective > interleave mempolicy. > > alloc_pages_exact_node() does not limit the allocation to the single > node, however, but rather prefers it. This is because __GFP_THISNODE is > not set which would cause the node-local nodemask to be passed. Without > it, only a nodemask that prefers the local node is passed.
Oops, good catch. But I believe we have the same problem with khugepaged_alloc_page(), rendering the recent node determination and zone_reclaim strictness patches partially useless.
Then I start to wonder about other alloc_pages_exact_node() users. Some do pass __GFP_THISNODE, others not - are they also mistaken? I guess the function is a misnomer - when I see "exact_node", I expect the __GFP_THISNODE behavior.
I think to avoid such hidden catches, we should create alloc_pages_preferred_node() variant, change the exact_node() variant to pass __GFP_THISNODE, and audit and adjust all callers accordingly.
Also, you pass __GFP_NOWARN but that should be covered by GFP_TRANSHUGE already. Of course, nothing guarantees that hugepage == true implies that gfp == GFP_TRANSHUGE... but current in-tree callers conform to that.
> Fix this by passing __GFP_THISNODE and falling back to small pages when > the allocation fails. > > Fixes: 077fcf116c8c ("mm/thp: allocate transparent hugepages on local node") > Signed-off-by: Greg Thelen <gthelen@google.com> > Signed-off-by: David Rientjes <rientjes@google.com> > --- > v2: GFP_THISNODE actually defers compaction and reclaim entirely based on > the combination of gfp flags. We want to try compaction and reclaim, > so only set __GFP_THISNODE. We still set __GFP_NOWARN to suppress > oom warnings in the kernel log when we can simply fallback to small > pages. > > mm/mempolicy.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > diff --git a/mm/mempolicy.c b/mm/mempolicy.c > --- a/mm/mempolicy.c > +++ b/mm/mempolicy.c > @@ -1985,7 +1985,10 @@ retry_cpuset: > nmask = policy_nodemask(gfp, pol); > if (!nmask || node_isset(node, *nmask)) { > mpol_cond_put(pol); > - page = alloc_pages_exact_node(node, gfp, order); > + page = alloc_pages_exact_node(node, gfp | > + __GFP_THISNODE | > + __GFP_NOWARN, > + order); > goto out; > } > } >
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