From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <owner-linux-mm@kvack.org>
Received: from mail-wr0-f197.google.com (mail-wr0-f197.google.com [209.85.128.197])
	by kanga.kvack.org (Postfix) with ESMTP id 9AAD76B03A4
	for <linux-mm@kvack.org>; Wed, 19 Apr 2017 08:16:42 -0400 (EDT)
Received: by mail-wr0-f197.google.com with SMTP id g31so2241117wrg.15
        for <linux-mm@kvack.org>; Wed, 19 Apr 2017 05:16:42 -0700 (PDT)
Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15])
        by mx.google.com with ESMTPS id q185si3823467wmg.28.2017.04.19.05.16.41
        for <linux-mm@kvack.org>
        (version=TLS1 cipher=AES128-SHA bits=128/128);
        Wed, 19 Apr 2017 05:16:41 -0700 (PDT)
Date: Wed, 19 Apr 2017 14:16:37 +0200
From: Michal Hocko <mhocko@kernel.org>
Subject: Re: [PATCH 1/3] mm: consider zone which is not fully populated to
 have holes
Message-ID: <20170419121637.GG29789@dhcp22.suse.cz>
References: <20170410110351.12215-1-mhocko@kernel.org>
 <20170415121734.6692-1-mhocko@kernel.org>
 <20170415121734.6692-2-mhocko@kernel.org>
 <97a658cd-e656-6efa-7725-150063d276f1@suse.cz>
 <20170418092757.GM22360@dhcp22.suse.cz>
 <12814e7e-5ed7-de1f-3e7c-9501eec1682a@suse.cz>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <12814e7e-5ed7-de1f-3e7c-9501eec1682a@suse.cz>
Sender: owner-linux-mm@kvack.org
List-ID: <linux-mm.kvack.org>
To: Vlastimil Babka <vbabka@suse.cz>, Joonsoo Kim <js1304@gmail.com>
Cc: linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>, Mel Gorman <mgorman@suse.de>, Andrea Arcangeli <aarcange@redhat.com>, Jerome Glisse <jglisse@redhat.com>, Reza Arbab <arbab@linux.vnet.ibm.com>, Yasuaki Ishimatsu <yasu.isimatu@gmail.com>, qiuxishi@huawei.com, Kani Toshimitsu <toshi.kani@hpe.com>, slaoub@gmail.com, Andi Kleen <ak@linux.intel.com>, David Rientjes <rientjes@google.com>, Daniel Kiper <daniel.kiper@oracle.com>, Igor Mammedov <imammedo@redhat.com>, Vitaly Kuznetsov <vkuznets@redhat.com>, LKML <linux-kernel@vger.kernel.org>

On Wed 19-04-17 13:59:40, Vlastimil Babka wrote:
> On 04/18/2017 11:27 AM, Michal Hocko wrote:
[...]
> > I am not aware of any such user. PageReserved has always been about "the
> > core mm should touch these pages and modify their state" AFAIR.
> > But I believe that touching those holes just asks for problems so I
> > would rather have them covered.
> 
> OK. I guess it's OK to use PageReserved of first pageblock page to
> determine if we can trust page_zone(), because the memory offline
> scenario should have sufficient granularity and not make holes inside
> pageblock?

Yes memblocks should be section size aligned and that is 128M resp. 2GB
on large machines. So we are talking about much larger than page block
granularity here.

Anyway, Joonsoo didn't like the the explicit PageReserved checks so I
have come with pfn_to_online_page which hides this implementation
detail. How do you like the following instead?
---