From: Mel Gorman Date: Thu, 2 Oct 2014 18:47:42 +0000 (+0100) Subject: mm: numa: Do not mark PTEs pte_numa when splitting huge pages X-Git-Tag: upstream/snapshot3+hdmi~1416 X-Git-Url: http://review.tizen.org/git/?p=platform%2Fadaptation%2Frenesas_rcar%2Frenesas_kernel.git;a=commitdiff_plain;h=5f50c44d8a63ee6c4801cdcb372b8048ac77efcf mm: numa: Do not mark PTEs pte_numa when splitting huge pages commit abc40bd2eeb77eb7c2effcaf63154aad929a1d5f upstream. 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 Acked-by: Rik van Riel Acked-by: Kirill A. Shutemov Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 4a0c998..718bfa1 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -1826,14 +1826,17 @@ static int __split_huge_page_map(struct page *page, for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) { pte_t *pte, entry; BUG_ON(PageCompound(page+i)); + /* + * Note that pmd_numa is not transferred deliberately + * to avoid any possibility that pte_numa leaks to + * a PROT_NONE VMA by accident. + */ entry = mk_pte(page + i, vma->vm_page_prot); entry = maybe_mkwrite(pte_mkdirty(entry), vma); if (!pmd_write(*pmd)) 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);