Date: Fri, 10 Mar 2017 13:00:37 -0600
From: Reza Arbab <arbab@linux.vnet.ibm.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: Igor Mammedov <imammedo@redhat.com>,
        Heiko Carstens <heiko.carstens@de.ibm.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>, linux-mm@kvack.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Greg KH <gregkh@linuxfoundation.org>,
        "K. Y. Srinivasan" <kys@microsoft.com>,
        David Rientjes <rientjes@google.com>,
        Daniel Kiper <daniel.kiper@oracle.com>, linux-api@vger.kernel.org,
        LKML <linux-kernel@vger.kernel.org>, linux-s390@vger.kernel.org,
        xen-devel@lists.xenproject.org, linux-acpi@vger.kernel.org,
        qiuxishi@huawei.com, toshi.kani@hpe.com, xieyisheng1@huawei.com,
        slaoub@gmail.com, iamjoonsoo.kim@lge.com, vbabka@suse.cz,
        Zhang Zhen <zhenzhang.zhang@huawei.com>,
        Yasuaki Ishimatsu <yasu.isimatu@gmail.com>,
        Tang Chen <tangchen@cn.fujitsu.com>
Subject: Re: WTH is going on with memory hotplug sysf interface (was: Re:
 [RFC PATCH] mm, hotplug: get rid of auto_online_blocks)
References: <1488462828-174523-1-git-send-email-imammedo@redhat.com>
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 <20170303183422.6358ee8f@nial.brq.redhat.com>
 <20170306145417.GG27953@dhcp22.suse.cz>
 <20170307134004.58343e14@nial.brq.redhat.com>
 <20170309125400.GI11592@dhcp22.suse.cz>
 <20170310135807.GI3753@dhcp22.suse.cz>
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On Fri, Mar 10, 2017 at 04:53:33PM +0100, Michal Hocko wrote:
>OK, so while I was playing with this setup some more I probably got why
>this is done this way. All new memblocks are added to the zone Normal
>where they are accounted as spanned but not present.

It's not always zone Normal. See zone_for_memory(). This leads to a 
workaround for having to do online_movable in descending block order. 
Instead of this:

1. probe block 34, probe block 33, probe block 32, ...
2. online_movable 34, online_movable 33, online_movable 32, ...

you can online_movable the first block before adding the rest:

1. probe block 32, online_movable 32
2. probe block 33, probe block 34, ...
	- zone_for_memory() will cause these to start Movable
3. online 33, online 34, ...
	- they're already in Movable, so online_movable is equivalentr

I agree with your general sentiment that this stuff is very 
nonintuitive.

-- 
Reza Arbab