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Date: Mon, 7 Oct 2013 11:28:50 +0100 From: Mel Gorman <mgorman@...e.de> To: Peter Zijlstra <a.p.zijlstra@...llo.nl>, Rik van Riel <riel@...hat.com> Cc: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>, Ingo Molnar <mingo@...nel.org>, Andrea Arcangeli <aarcange@...hat.com>, Johannes Weiner <hannes@...xchg.org>, Linux-MM <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>, Mel Gorman <mgorman@...e.de> Subject: [PATCH 12/63] mm: numa: Do not migrate or account for hinting faults on the zero page The zero page is not replicated between nodes and is often shared between processes. The data is read-only and likely to be cached in local CPUs if heavily accessed meaning that the remote memory access cost is less of a concern. This patch prevents trapping faults on the zero pages. For tasks using the zero page this will reduce the number of PTE updates, TLB flushes and hinting faults. [peterz@...radead.org: Correct use of is_huge_zero_page] Signed-off-by: Mel Gorman <mgorman@...e.de> --- mm/huge_memory.c | 10 +++++++++- mm/memory.c | 1 + 2 files changed, 10 insertions(+), 1 deletion(-) diff --git a/mm/huge_memory.c b/mm/huge_memory.c index de8d5cf..8677dbf 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -1291,6 +1291,7 @@ int do_huge_pmd_numa_page(struct mm_struct *mm, struct vm_area_struct *vma, goto out_unlock; page = pmd_page(pmd); + BUG_ON(is_huge_zero_page(page)); page_nid = page_to_nid(page); count_vm_numa_event(NUMA_HINT_FAULTS); if (page_nid == this_nid) @@ -1481,8 +1482,15 @@ int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, } else { struct page *page = pmd_page(*pmd); - /* only check non-shared pages */ + /* + * Only check non-shared pages. Do not trap faults + * against the zero page. The read-only data is likely + * to be read-cached on the local CPU cache and it is + * less useful to know about local vs remote hits on + * the zero page. + */ if (page_mapcount(page) == 1 && + !is_huge_zero_page(page) && !pmd_numa(*pmd)) { entry = pmdp_get_and_clear(mm, addr, pmd); entry = pmd_mknuma(entry); diff --git a/mm/memory.c b/mm/memory.c index 42ae82e..ed51f15 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -3564,6 +3564,7 @@ int do_numa_page(struct mm_struct *mm, struct vm_area_struct *vma, pte_unmap_unlock(ptep, ptl); return 0; } + BUG_ON(is_zero_pfn(page_to_pfn(page))); page_nid = page_to_nid(page); target_nid = numa_migrate_prep(page, vma, addr, page_nid); -- 1.8.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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