From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753327AbbJFPYT (ORCPT ); Tue, 6 Oct 2015 11:24:19 -0400 Received: from mga03.intel.com ([134.134.136.65]:51301 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752983AbbJFPYQ (ORCPT ); Tue, 6 Oct 2015 11:24:16 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.17,644,1437462000"; d="scan'208";a="820637936" 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: [PATCHv12 04/37] mm, thp: adjust conditions when we can reuse the page on WP fault Date: Tue, 6 Oct 2015 18:23:31 +0300 Message-Id: <1444145044-72349-5-git-send-email-kirill.shutemov@linux.intel.com> X-Mailer: git-send-email 2.5.3 In-Reply-To: <1444145044-72349-1-git-send-email-kirill.shutemov@linux.intel.com> References: <1444145044-72349-1-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, 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 9c7c4b418498..1184fdbd30ba 100644 --- a/include/linux/swap.h +++ b/include/linux/swap.h @@ -540,7 +540,8 @@ 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 7c41c0606e98..76a845b12d8d 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -1230,7 +1230,17 @@ 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 f131bc1838d3..c6aec93c8c0b 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); -- 2.5.3