Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758374AbbDWVKT (ORCPT ); Thu, 23 Apr 2015 17:10:19 -0400 Received: from mga14.intel.com ([192.55.52.115]:46126 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758459AbbDWVE3 (ORCPT ); Thu, 23 Apr 2015 17:04:29 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.11,634,1422950400"; d="scan'208";a="718320668" 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: [PATCHv5 06/28] mm: handle PTE-mapped tail pages in gerneric fast gup implementaiton Date: Fri, 24 Apr 2015 00:03:41 +0300 Message-Id: <1429823043-157133-7-git-send-email-kirill.shutemov@linux.intel.com> X-Mailer: git-send-email 2.1.4 In-Reply-To: <1429823043-157133-1-git-send-email-kirill.shutemov@linux.intel.com> References: <1429823043-157133-1-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: 1880 Lines: 58 With new refcounting we are going to see THP tail pages mapped with PTE. Generic fast GUP rely on page_cache_get_speculative() to obtain reference on page. page_cache_get_speculative() always fails on tail pages, because ->_count on tail pages is always zero. Let's handle tail pages in gup_pte_range(). New split_huge_page() will rely on migration entries to freeze page's counts. Recheck PTE value after page_cache_get_speculative() on head page should be enough to serialize against split. Signed-off-by: Kirill A. Shutemov Tested-by: Sasha Levin --- mm/gup.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/mm/gup.c b/mm/gup.c index ebdb39b3e820..eaeeae15006b 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -1051,7 +1051,7 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end, * for an example see gup_get_pte in arch/x86/mm/gup.c */ pte_t pte = READ_ONCE(*ptep); - struct page *page; + struct page *head, *page; /* * Similar to the PMD case below, NUMA hinting must take slow @@ -1063,15 +1063,17 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end, VM_BUG_ON(!pfn_valid(pte_pfn(pte))); page = pte_page(pte); + head = compound_head(page); - if (!page_cache_get_speculative(page)) + if (!page_cache_get_speculative(head)) goto pte_unmap; if (unlikely(pte_val(pte) != pte_val(*ptep))) { - put_page(page); + put_page(head); goto pte_unmap; } + VM_BUG_ON_PAGE(compound_head(page) != head, page); pages[*nr] = page; (*nr)++; -- 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/