From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx135.postini.com [74.125.245.135]) by kanga.kvack.org (Postfix) with SMTP id E3A6F6B003D for ; Tue, 10 Sep 2013 05:32:43 -0400 (EDT) From: Mel Gorman Subject: [PATCH 09/50] mm: numa: Do not migrate or account for hinting faults on the zero page Date: Tue, 10 Sep 2013 10:31:49 +0100 Message-Id: <1378805550-29949-10-git-send-email-mgorman@suse.de> In-Reply-To: <1378805550-29949-1-git-send-email-mgorman@suse.de> References: <1378805550-29949-1-git-send-email-mgorman@suse.de> Sender: owner-linux-mm@kvack.org List-ID: To: Peter Zijlstra , Rik van Riel Cc: Srikar Dronamraju , Ingo Molnar , Andrea Arcangeli , Johannes Weiner , Linux-MM , LKML , Mel Gorman 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@infradead.org: Correct use of is_huge_zero_page] Signed-off-by: Mel Gorman --- mm/huge_memory.c | 7 ++++++- mm/memory.c | 1 + mm/mprotect.c | 10 +++++++++- 3 files changed, 16 insertions(+), 2 deletions(-) diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 94d0739..40f75a6 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -1303,6 +1303,7 @@ 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) @@ -1488,8 +1489,12 @@ 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. See change_pte_range + * for comment on why the zero page is not modified + */ if (page_mapcount(page) == 1 && + !is_huge_zero_page(page) && !pmd_numa(*pmd)) { entry = pmd_mknuma(entry); } diff --git a/mm/memory.c b/mm/memory.c index c20f872..86c3caf 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -3575,6 +3575,7 @@ 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); diff --git a/mm/mprotect.c b/mm/mprotect.c index 2bbb648..faa499e 100644 --- a/mm/mprotect.c +++ b/mm/mprotect.c @@ -62,7 +62,15 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd, struct page *page; page = vm_normal_page(vma, addr, oldpte); - if (page) { + + /* + * 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 && !is_zero_pfn(page_to_pfn(page))) { int this_nid = page_to_nid(page); if (last_nid == -1) last_nid = this_nid; -- 1.8.1.4 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org