Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933341AbcCKXGJ (ORCPT ); Fri, 11 Mar 2016 18:06:09 -0500 Received: from mga03.intel.com ([134.134.136.65]:59008 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753114AbcCKW7f (ORCPT ); Fri, 11 Mar 2016 17:59:35 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.24,321,1455004800"; d="scan'208";a="762612781" From: "Kirill A. Shutemov" To: Hugh Dickins , Andrea Arcangeli , Andrew Morton Cc: Dave Hansen , Vlastimil Babka , Christoph Lameter , Naoya Horiguchi , Jerome Marchand , Yang Shi , Sasha Levin , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, "Kirill A. Shutemov" Subject: [PATCHv4 10/25] thp: handle file COW faults Date: Sat, 12 Mar 2016 01:59:02 +0300 Message-Id: <1457737157-38573-11-git-send-email-kirill.shutemov@linux.intel.com> X-Mailer: git-send-email 2.7.0 In-Reply-To: <1457737157-38573-1-git-send-email-kirill.shutemov@linux.intel.com> References: <1457737157-38573-1-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: 982 Lines: 32 File COW for THP is handled on pte level: just split the pmd. It's not clear how benefitial would be allocation of huge pages on COW faults. And it would require some code to make them work. I think at some point we can consider teaching khugepaged to collapse pages in COW mappings, but allocating huge on fault is probably overkill. Signed-off-by: Kirill A. Shutemov --- mm/memory.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/mm/memory.c b/mm/memory.c index f7a73b6cabac..c0a2510b9e15 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -3366,6 +3366,11 @@ static int wp_huge_pmd(struct fault_env *fe, pmd_t orig_pmd) if (fe->vma->vm_ops->pmd_fault) return fe->vma->vm_ops->pmd_fault(fe->vma, fe->address, fe->pmd, fe->flags); + + /* COW handled on pte level: split pmd */ + VM_BUG_ON_VMA(fe->vma->vm_flags & VM_SHARED, fe->vma); + split_huge_pmd(fe->vma, fe->pmd, fe->address); + return VM_FAULT_FALLBACK; } -- 2.7.0