From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f70.google.com (mail-wm0-f70.google.com [74.125.82.70]) by kanga.kvack.org (Postfix) with ESMTP id 50E0682F64 for ; Mon, 5 Sep 2016 10:18:44 -0400 (EDT) Received: by mail-wm0-f70.google.com with SMTP id w12so9275560wmf.3 for ; Mon, 05 Sep 2016 07:18:44 -0700 (PDT) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id i89si17608998wmc.142.2016.09.05.07.18.42 for (version=TLS1 cipher=AES128-SHA bits=128/128); Mon, 05 Sep 2016 07:18:43 -0700 (PDT) Subject: Re: [PATCH] mem-hotplug: Don't clear the only node in new_node_page() References: <1473044391.4250.19.camel@TP420> From: Vlastimil Babka Message-ID: Date: Mon, 5 Sep 2016 16:18:29 +0200 MIME-Version: 1.0 In-Reply-To: <1473044391.4250.19.camel@TP420> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Li Zhong , linux-mm Cc: jallen@linux.vnet.ibm.com, qiuxishi@huawei.com, iamjoonsoo.kim@lge.com, n-horiguchi@ah.jp.nec.com, rientjes@google.com, Andrew Morton , Michal Hocko , Tetsuo Handa On 09/05/2016 04:59 AM, Li Zhong wrote: > Commit 394e31d2c introduced new_node_page() for memory hotplug. > > In new_node_page(), the nid is cleared before calling __alloc_pages_nodemask(). > But if it is the only node of the system, So the use case is that we are partially offlining the only online node? > and the first round allocation fails, > it will not be able to get memory from an empty nodemask, and trigger oom. Hmm triggering OOM due to empty nodemask sounds like a wrong thing to do. CCing some OOM experts for insight. Also OOM is skipped for __GFP_THISNODE allocations, so we might also consider the same for nodemask-constrained allocations? > The patch checks whether it is the last node on the system, and if it is, then > don't clear the nid in the nodemask. I'd rather see the allocation not OOM, and rely on the fallback in new_node_page() that doesn't have nodemask. But I suspect it might also make sense to treat empty nodemask as something unexpected and put some WARN_ON (instead of OOM) in the allocator. > Reported-by: John Allen > Signed-off-by: Li Zhong Acked-by: Vlastimil Babka Fixes: 394e31d2ceb4 ("mem-hotplug: alloc new page from a nearest neighbor node when mem-offline") > --- > mm/memory_hotplug.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c > index 41266dc..b58906b 100644 > --- a/mm/memory_hotplug.c > +++ b/mm/memory_hotplug.c > @@ -1567,7 +1567,9 @@ static struct page *new_node_page(struct page *page, unsigned long private, > return alloc_huge_page_node(page_hstate(compound_head(page)), > next_node_in(nid, nmask)); > > - node_clear(nid, nmask); > + if (nid != next_node_in(nid, nmask)) > + node_clear(nid, nmask); > + > if (PageHighMem(page) > || (zone_idx(page_zone(page)) == ZONE_MOVABLE)) > gfp_mask |= __GFP_HIGHMEM; > > > -- 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