From patchwork Wed Jun 15 20:06:11 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Kirill A . Shutemov" X-Patchwork-Id: 9179421 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 15376604DB for ; Wed, 15 Jun 2016 20:19:36 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 0351F26B4A for ; Wed, 15 Jun 2016 20:19:36 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id EC00E27F07; Wed, 15 Jun 2016 20:19:35 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.9 required=2.0 tests=BAYES_00,RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 8228A26B4A for ; Wed, 15 Jun 2016 20:19:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1161071AbcFOUTJ (ORCPT ); Wed, 15 Jun 2016 16:19:09 -0400 Received: from mga02.intel.com ([134.134.136.20]:54748 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932904AbcFOUG6 (ORCPT ); Wed, 15 Jun 2016 16:06:58 -0400 Received: from fmsmga001.fm.intel.com ([10.253.24.23]) by orsmga101.jf.intel.com with ESMTP; 15 Jun 2016 13:06:58 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.26,477,1459839600"; d="scan'208";a="988242042" Received: from black.fi.intel.com ([10.237.72.93]) by fmsmga001.fm.intel.com with ESMTP; 15 Jun 2016 13:06:54 -0700 Received: by black.fi.intel.com (Postfix, from userid 1000) id D4696666; Wed, 15 Jun 2016 23:06:48 +0300 (EEST) 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, Ebru Akagunduz , "Kirill A. Shutemov" Subject: [PATCHv9-rebased2 06/37] thp, mlock: update unevictable-lru.txt Date: Wed, 15 Jun 2016 23:06:11 +0300 Message-Id: <1466021202-61880-7-git-send-email-kirill.shutemov@linux.intel.com> X-Mailer: git-send-email 2.8.1 In-Reply-To: <1466021202-61880-1-git-send-email-kirill.shutemov@linux.intel.com> References: <1465222029-45942-1-git-send-email-kirill.shutemov@linux.intel.com> <1466021202-61880-1-git-send-email-kirill.shutemov@linux.intel.com> Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP 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 -------------------------------------