Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755227AbaKEOwy (ORCPT ); Wed, 5 Nov 2014 09:52:54 -0500 Received: from mga01.intel.com ([192.55.52.88]:62488 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755108AbaKEOuQ (ORCPT ); Wed, 5 Nov 2014 09:50:16 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.07,320,1413270000"; d="scan'208";a="617582810" From: "Kirill A. Shutemov" To: Andrew Morton , Andrea Arcangeli Cc: Dave Hansen , Hugh Dickins , Mel Gorman , Rik van Riel , Vlastimil Babka , Christoph Lameter , Naoya Horiguchi , Steve Capper , "Aneesh Kumar K.V" , Johannes Weiner , Michal Hocko , linux-kernel@vger.kernel.org, linux-mm@kvack.org, "Kirill A. Shutemov" Subject: [PATCH 07/19] mm, thp: adjust conditions when we can reuse the page on WP fault Date: Wed, 5 Nov 2014 16:49:42 +0200 Message-Id: <1415198994-15252-8-git-send-email-kirill.shutemov@linux.intel.com> X-Mailer: git-send-email 2.1.1 In-Reply-To: <1415198994-15252-1-git-send-email-kirill.shutemov@linux.intel.com> References: <1415198994-15252-1-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 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 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. Signed-off-by: Kirill A. Shutemov --- include/linux/swap.h | 8 +++++++- mm/huge_memory.c | 12 +++++++++++- mm/swapfile.c | 3 +++ 3 files changed, 21 insertions(+), 2 deletions(-) diff --git a/include/linux/swap.h b/include/linux/swap.h index 1b72060f093a..79333ea921c8 100644 --- a/include/linux/swap.h +++ b/include/linux/swap.h @@ -555,7 +555,13 @@ static inline int page_swapcount(struct page *page) return 0; } -#define reuse_swap_page(page) (page_mapcount(page) == 1) +static inline int reuse_swap_page(struct page *page) +{ + /* The page is part of THP and cannot be reused */ + if (PageTransCompound(page)) + return 0; + return 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 869f9bcf481e..aa22350673a7 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -1106,7 +1106,17 @@ 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 57252bb35041..dfc81ba15697 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -887,6 +887,9 @@ 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); -- 2.1.1 -- 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/