linux-kernel - Re: [PATCH v2] memory_hotplug: zone_can

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Message-Id: <20161213231236.g6prnnjy6nyt4qkf@arbab-laptop>
Date:   Tue, 13 Dec 2016 17:12:36 -0600
From:   Reza Arbab <arbab@...ux.vnet.ibm.com>
To:     Yasuaki Ishimatsu <yasu.isimatu@...il.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        isimatu.yasuaki@...fujitsu.com
Subject: Re: [PATCH v2] memory_hotplug: zone_can_shift() returns boolean value

On Tue, Dec 13, 2016 at 03:29:49PM -0500, Yasuaki Ishimatsu wrote:
>online_{kernel|movable} is used to change the memory zone to
>ZONE_{NORMAL|MOVABLE} and online the memory.
>
>To check that memory zone can be changed, zone_can_shift() is used.
>Currently the function returns minus integer value, plus integer
>value and 0. When the function returns minus or plus integer value,
>it means that the memory zone can be changed to ZONE_{NORNAL|MOVABLE}.
>
>But when the function returns 0, there is 2 meanings.
>
>One of the meanings is that the memory zone does not need to be changed.
>For example, when memory is in ZONE_NORMAL and onlined by online_kernel
>the memory zone does not need to be changed.
>
>Another meaning is that the memory zone cannot be changed. When memory
>is in ZONE_NORMAL and onlined by online_movable, the memory zone may
>not be changed to ZONE_MOVALBE due to memory online limitation(see
>Documentation/memory-hotplug.txt). In this case, memory must not be
>onlined.
>
>The patch changes the return type of zone_can_shift() so that memory
>is not onlined when memory zone cannot be changed.

Reviewed-by: Reza Arbab <arbab@...ux.vnet.ibm.com>

-- 
Reza Arbab