From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wj0-f200.google.com (mail-wj0-f200.google.com [209.85.210.200]) by kanga.kvack.org (Postfix) with ESMTP id AF6C56B0033 for ; Tue, 7 Feb 2017 04:45:59 -0500 (EST) Received: by mail-wj0-f200.google.com with SMTP id c7so24238942wjb.7 for ; Tue, 07 Feb 2017 01:45:59 -0800 (PST) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id g10si4357333wrc.189.2017.02.07.01.45.58 for (version=TLS1 cipher=AES128-SHA bits=128/128); Tue, 07 Feb 2017 01:45:58 -0800 (PST) Date: Tue, 7 Feb 2017 10:45:57 +0100 From: Michal Hocko Subject: Re: [PATCH] mm/page_alloc: return 0 in case this node has no page within the zone Message-ID: <20170207094557.GE5065@dhcp22.suse.cz> References: <20170206154314.15705-1-richard.weiyang@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170206154314.15705-1-richard.weiyang@gmail.com> Sender: owner-linux-mm@kvack.org List-ID: To: Wei Yang Cc: akpm@linux-foundation.org, vbabka@suse.cz, mgorman@techsingularity.net, linux-mm@kvack.org, linux-kernel@vger.kernel.org On Mon 06-02-17 23:43:14, Wei Yang wrote: > The whole memory space is divided into several zones and nodes may have no > page in some zones. In this case, the __absent_pages_in_range() would > return 0, since the range it is searching for is an empty range. > > Also this happens more often to those nodes with higher memory range when > there are more nodes, which is a trend for future architectures. I do not understand this part. Why would we see more zones with zero pfn range in higher memory ranges. > This patch checks the zone range after clamp and adjustment, return 0 if > the range is an empty range. I assume the whole point of this patch is to save __absent_pages_in_range which iterates over all memblock regions, right? Is there any reason why for_each_mem_pfn_range cannot be changed to honor the given start/end pfns instead? I can imagine that a small zone would see a similar pointless iterations... > Signed-off-by: Wei Yang > --- > mm/page_alloc.c | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 6de9440e3ae2..51c60c0eadcb 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -5521,6 +5521,11 @@ static unsigned long __meminit zone_absent_pages_in_node(int nid, > adjust_zone_range_for_zone_movable(nid, zone_type, > node_start_pfn, node_end_pfn, > &zone_start_pfn, &zone_end_pfn); > + > + /* If this node has no page within this zone, return 0. */ > + if (zone_start_pfn == zone_end_pfn) > + return 0; > + > nr_absent = __absent_pages_in_range(nid, zone_start_pfn, zone_end_pfn); > > /* > -- > 2.11.0 > > -- > 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 -- Michal Hocko SUSE Labs -- 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