Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752749AbcDPAYV (ORCPT ); Fri, 15 Apr 2016 20:24:21 -0400 Received: from mga14.intel.com ([192.55.52.115]:12523 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752553AbcDPAYR (ORCPT ); Fri, 15 Apr 2016 20:24:17 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.24,489,1455004800"; d="scan'208";a="933504950" 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 , Andres Lagar-Cavilla , Ning Qu , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, "Kirill A. Shutemov" Subject: [PATCHv7 01/29] thp, mlock: update unevictable-lru.txt Date: Sat, 16 Apr 2016 03:23:32 +0300 Message-Id: <1460766240-84565-2-git-send-email-kirill.shutemov@linux.intel.com> X-Mailer: git-send-email 2.8.0.rc3 In-Reply-To: <1460766240-84565-1-git-send-email-kirill.shutemov@linux.intel.com> References: <1460766240-84565-1-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: 1609 Lines: 41 Add description of THP handling into unevictable-lru.txt. Signed-off-by: Kirill A. Shutemov --- Documentation/vm/unevictable-lru.txt | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+) diff --git a/Documentation/vm/unevictable-lru.txt b/Documentation/vm/unevictable-lru.txt index fa3b527086fa..0026a8d33fc0 100644 --- a/Documentation/vm/unevictable-lru.txt +++ b/Documentation/vm/unevictable-lru.txt @@ -461,6 +461,27 @@ unevictable LRU is enabled, the work of compaction is mostly handled by the page migration code and the same work flow as described in MIGRATING MLOCKED PAGES will apply. +MLOCKING TRANSPARENT HUGE PAGES +------------------------------- + +A transparent huge page is represented by a single entry on an LRU list. +Therefore, we can only make unevictable an entire compound page, not +individual subpages. + +If a user tries to mlock() part of a huge page, we want the rest of the +page to be reclaimable. + +We cannot just split the page on partial mlock() as split_huge_page() can +fail and new intermittent failure mode for the syscall is undesirable. + +We handle this by keeping PTE-mapped huge pages on normal LRU lists: the +PMD on border of VM_LOCKED VMA will be split into PTE table. + +This way the huge page is accessible for vmscan. Under memory pressure the +page will be split, subpages which belong to VM_LOCKED VMAs will be moved +to unevictable LRU and the rest can be reclaimed. + +See also comment in follow_trans_huge_pmd(). mmap(MAP_LOCKED) SYSTEM CALL HANDLING ------------------------------------- -- 2.8.0.rc3