From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752331AbbASJq7 (ORCPT ); Mon, 19 Jan 2015 04:46:59 -0500 Received: from cantor2.suse.de ([195.135.220.15]:50502 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751293AbbASJq6 (ORCPT ); Mon, 19 Jan 2015 04:46:58 -0500 Date: Mon, 19 Jan 2015 10:46:56 +0100 From: Michal Hocko To: "long.wanglong" Cc: hannes@cmpxchg.org, shijie8@gmail.com, torvalds@linux-foundation.org, azurit@pobox.sk, hugh.dickins@tiscali.co.uk, rientjes@google.com, kosaki.motohiro@jp.fujitsu.com, "linux-kernel@vger.kernel.org" , peifeiyue@huawei.com Subject: Re: does the semantics of MAP_LOCKED is equal to mlock() function? Message-ID: <20150119094656.GA21052@dhcp22.suse.cz> References: <54BCA187.6070601@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <54BCA187.6070601@huawei.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org See http://marc.info/?l=linux-mm&m=142122902313315&w=2 for more information. On Mon 19-01-15 14:17:43, long.wanglong wrote: > Hi all: > > In the latest kernel, i set the memory limit (4096) in a test cgroup. and add the test task. > the test code code is: > > testcase 1: mmap with MAP_LOCKED flag(memsize = 8192) > > 185 p = mmap(NULL, memsize, PROT_WRITE | PROT_READ, > 186 MAP_PRIVATE | MAP_ANONYMOUS | MAP_LOCKED, 0, 0); > 187 if (p == MAP_FAILED) > 188 err(1, "mmap(lock) failed"); > > expect: invoke OOM killer. > result: not invoke OOM killer. > > > testcase 2: mmap without MAP_LOCKED flag and the call mlock (memsize = 8192) > > 185 p = mmap(NULL, memsize, PROT_WRITE | PROT_READ, > 186 MAP_PRIVATE | MAP_ANONYMOUS, 0, 0); > 187 if (p == MAP_FAILED) > 188 err(1, "mmap(lock) failed"); > 189 > 190 if (mlock(p, memsize) == -1) > 191 err(1, "mlock failed") > > expect: invoke OOM killer. > result: invoke OOM killer. > > in the Linux Programmer's Manual: > > MAP_LOCKED (since Linux 2.5.37) > Lock the pages of the mapped region into memory in the manner > of mlock(2). This flag is ignored in older kernels. > > and > mlock() locks pages in the address range starting at addr and > continuing for len bytes. All pages that contain a part of the > specified address range are guaranteed to be resident in RAM when the > call returns successfully; the pages are guaranteed to stay in RAM > until later unlocked. > > According to the description in the manual, the two testcases are equivalent. > > why the first testcase does not invoke OOM killer? > does the mmap with MAP_LOCKED flag will not immediately allocate physical memory? > > > Best Regards > Wang Long > -- Michal Hocko SUSE Labs