From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi0-f71.google.com (mail-oi0-f71.google.com [209.85.218.71]) by kanga.kvack.org (Postfix) with ESMTP id CD5AA6B0038 for ; Mon, 20 Feb 2017 12:09:51 -0500 (EST) Received: by mail-oi0-f71.google.com with SMTP id z13so25387764oig.0 for ; Mon, 20 Feb 2017 09:09:51 -0800 (PST) Received: from mx0a-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com. [148.163.158.5]) by mx.google.com with ESMTPS id p197si13302462wmg.0.2017.02.20.09.09.50 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 20 Feb 2017 09:09:51 -0800 (PST) Received: from pps.filterd (m0098413.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.20/8.16.0.20) with SMTP id v1KH8bhT098753 for ; Mon, 20 Feb 2017 12:09:49 -0500 Received: from e06smtp14.uk.ibm.com (e06smtp14.uk.ibm.com [195.75.94.110]) by mx0b-001b2d01.pphosted.com with ESMTP id 28r4dt0jkf-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Mon, 20 Feb 2017 12:09:49 -0500 Received: from localhost by e06smtp14.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 20 Feb 2017 17:09:47 -0000 Subject: Re: [PATCH] mm/cgroup: avoid panic when init with low memory References: <1487154969-6704-1-git-send-email-ldufour@linux.vnet.ibm.com> <20170220130123.GI2431@dhcp22.suse.cz> From: Laurent Dufour Date: Mon, 20 Feb 2017 18:09:43 +0100 MIME-Version: 1.0 In-Reply-To: <20170220130123.GI2431@dhcp22.suse.cz> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Message-Id: <934d40ec-060b-4794-2fdc-35a7ea1dc9e2@linux.vnet.ibm.com> Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Johannes Weiner , Vladimir Davydov , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org On 20/02/2017 14:01, Michal Hocko wrote: > On Wed 15-02-17 11:36:09, Laurent Dufour wrote: >> The system may panic when initialisation is done when almost all the >> memory is assigned to the huge pages using the kernel command line >> parameter hugepage=xxxx. Panic may occur like this: > > I am pretty sure the system might blow up in many other ways when you > misconfigure it and pull basically all the memory out. Anyway... > > [...] > >> This is a chicken and egg issue where the kernel try to get free >> memory when allocating per node data in mem_cgroup_init(), but in that >> path mem_cgroup_soft_limit_reclaim() is called which assumes that >> these data are allocated. >> >> As mem_cgroup_soft_limit_reclaim() is best effort, it should return >> when these data are not yet allocated. > > ... this makes some sense. Especially when there is no soft limit > configured. So this is a good step. I would just like to ask you to go > one step further. Can we make the whole soft reclaim thing uninitialized > until the soft limit is actually set? Soft limit is not used in cgroup > v2 at all and I would strongly discourage it in v1 as well. We will save > few bytes as a bonus. Hi Michal, and thanks for the review. I'm not familiar with that part of the kernel, so to be sure we are on the same line, are you suggesting to set soft_limit_tree at the first time mem_cgroup_write() is called to set a soft_limit field ? Obviously, all callers to soft_limit_tree_node() and soft_limit_tree_from_page() will have to check for the return pointer to be NULL. Cheers, Laurent. >> Signed-off-by: Laurent Dufour >> --- >> mm/memcontrol.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/mm/memcontrol.c b/mm/memcontrol.c >> index 1fd6affcdde7..213f96b2f601 100644 >> --- a/mm/memcontrol.c >> +++ b/mm/memcontrol.c >> @@ -2556,7 +2556,7 @@ unsigned long mem_cgroup_soft_limit_reclaim(pg_data_t *pgdat, int order, >> * is empty. Do it lockless to prevent lock bouncing. Races >> * are acceptable as soft limit is best effort anyway. >> */ >> - if (RB_EMPTY_ROOT(&mctz->rb_root)) >> + if (!mctz || RB_EMPTY_ROOT(&mctz->rb_root)) >> return 0; >> >> /* >> -- >> 2.7.4 > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org