linux-kernel - Re: Memory hotplug not increasing the total RAM

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Message-ID: <20180130091600.GA26445@dhcp22.suse.cz>
Date:   Tue, 30 Jan 2018 10:16:00 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Bharata B Rao <bharata@...ux.vnet.ibm.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        pasha.tatashin@...cle.com
Subject: Re: Memory hotplug not increasing the total RAM

On Tue 30-01-18 14:00:06, Bharata B Rao wrote:
> Hi,
> 
> With the latest upstream, I see that memory hotplug is not working
> as expected. The hotplugged memory isn't seen to increase the total
> RAM pages. This has been observed with both x86 and Power guests.
> 
> 1. Memory hotplug code intially marks pages as PageReserved via
> __add_section().
> 2. Later the struct page gets cleared in __init_single_page().
> 3. Next online_pages_range() increments totalram_pages only when
>    PageReserved is set.

You are right. I have completely forgot about this late struct page
initialization during onlining. memory hotplug really doesn't want
zeroying. Let me think about a fix.
-- 
Michal Hocko
SUSE Labs