Messages in this thread Patch in this message | | | From | Mel Gorman <> | Subject | [PATCH 4/4] mm: numa: Do not mark PTEs pte_numa when splitting huge pages | Date | Thu, 2 Oct 2014 14:29:18 +0100 |
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This patch reverts 1ba6e0b50b ("mm: numa: split_huge_page: transfer the NUMA type from the pmd to the pte"). If a huge page is being split due a protection change and the tail will be in a PROT_NONE vma then NUMA hinting PTEs are temporarily created in the protected VMA.
VM_RW|VM_PROTNONE |-----------------| ^ split here
In the specific case above, it should get fixed up by change_pte_range() but there is a window of opportunity for weirdness to happen. Similarly, if a huge page is shrunk and split during a protection update but before pmd_numa is cleared then a pte_numa can be left behind.
Instead of adding complexity trying to deal with the case, this patch will not mark PTEs NUMA when splitting a huge page. NUMA hinting faults will not be triggered which is marginal in comparison to the complexity in dealing with the corner cases during THP split.
Signed-off-by: Mel Gorman <mgorman@suse.de> --- mm/huge_memory.c | 2 -- 1 file changed, 2 deletions(-)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c index d9a21d06..17a74d6 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -1801,8 +1801,6 @@ static int __split_huge_page_map(struct page *page, entry = pte_wrprotect(entry); if (!pmd_young(*pmd)) entry = pte_mkold(entry); - if (pmd_numa(*pmd)) - entry = pte_mknuma(entry); pte = pte_offset_map(&_pmd, haddr); BUG_ON(!pte_none(*pte)); set_pte_at(mm, haddr, pte, entry); -- 1.8.4.5
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