Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932888AbbGTOdh (ORCPT ); Mon, 20 Jul 2015 10:33:37 -0400 Received: from mga03.intel.com ([134.134.136.65]:56852 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932262AbbGTOVT (ORCPT ); Mon, 20 Jul 2015 10:21:19 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.15,508,1432623600"; d="scan'208";a="765985110" From: "Kirill A. Shutemov" To: Andrew Morton , Andrea Arcangeli , Hugh Dickins Cc: Dave Hansen , Mel Gorman , Rik van Riel , Vlastimil Babka , Christoph Lameter , Naoya Horiguchi , Steve Capper , "Aneesh Kumar K.V" , Johannes Weiner , Michal Hocko , Jerome Marchand , Sasha Levin , linux-kernel@vger.kernel.org, linux-mm@kvack.org, "Kirill A. Shutemov" Subject: [PATCHv9 04/36] mm, thp: adjust conditions when we can reuse the page on WP fault Date: Mon, 20 Jul 2015 17:20:37 +0300 Message-Id: <1437402069-105900-5-git-send-email-kirill.shutemov@linux.intel.com> X-Mailer: git-send-email 2.1.4 In-Reply-To: <1437402069-105900-1-git-send-email-kirill.shutemov@linux.intel.com> References: <1437402069-105900-1-git-send-email-kirill.shutemov@linux.intel.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3244 Lines: 87 With new refcounting we will be able map the same compound page with PTEs and PMDs. It requires adjustment to conditions when we can reuse the page on write-protection fault. For PTE fault we can't reuse the page if it's part of huge page. For PMD we can only reuse the page if nobody else maps the huge page or it's part. We can do it by checking page_mapcount() on each sub-page, but it's expensive. The cheaper way is to check page_count() to be equal 1: every mapcount takes page reference, so this way we can guarantee, that the PMD is the only mapping. This approach can give false negative if somebody pinned the page, but that doesn't affect correctness. Signed-off-by: Kirill A. Shutemov Tested-by: Sasha Levin Tested-by: Aneesh Kumar K.V Acked-by: Jerome Marchand Acked-by: Vlastimil Babka --- include/linux/swap.h | 3 ++- mm/huge_memory.c | 12 +++++++++++- mm/swapfile.c | 3 +++ 3 files changed, 16 insertions(+), 2 deletions(-) diff --git a/include/linux/swap.h b/include/linux/swap.h index ec62fcbfcad3..24ad6c3b0853 100644 --- a/include/linux/swap.h +++ b/include/linux/swap.h @@ -537,7 +537,8 @@ static inline int swp_swapcount(swp_entry_t entry) return 0; } -#define reuse_swap_page(page) (page_mapcount(page) == 1) +#define reuse_swap_page(page) \ + (!PageTransCompound(page) && page_mapcount(page) == 1) static inline int try_to_free_swap(struct page *page) { diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 6fd6df16e55d..8d5a8881c60e 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -1171,7 +1171,17 @@ int do_huge_pmd_wp_page(struct mm_struct *mm, struct vm_area_struct *vma, page = pmd_page(orig_pmd); VM_BUG_ON_PAGE(!PageCompound(page) || !PageHead(page), page); - if (page_mapcount(page) == 1) { + /* + * We can only reuse the page if nobody else maps the huge page or it's + * part. We can do it by checking page_mapcount() on each sub-page, but + * it's expensive. + * The cheaper way is to check page_count() to be equal 1: every + * mapcount takes page reference reference, so this way we can + * guarantee, that the PMD is the only mapping. + * This can give false negative if somebody pinned the page, but that's + * fine. + */ + if (page_mapcount(page) == 1 && page_count(page) == 1) { pmd_t entry; entry = pmd_mkyoung(orig_pmd); entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma); diff --git a/mm/swapfile.c b/mm/swapfile.c index 866c982cea9b..89ea6af27dc0 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -929,6 +929,9 @@ int reuse_swap_page(struct page *page) VM_BUG_ON_PAGE(!PageLocked(page), page); if (unlikely(PageKsm(page))) return 0; + /* The page is part of THP and cannot be reused */ + if (PageTransCompound(page)) + return 0; count = page_mapcount(page); if (count <= 1 && PageSwapCache(page)) { count += page_swapcount(page); -- 2.1.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/