On 02/25/2015 12:24 AM, David Rientjes wrote:
From: Greg Thelen <gthe...@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 <gthe...@google.com>
Signed-off-by: David Rientjes <rient...@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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