linux-kernel - Memory hotplug not increasing the total RAM

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Message-Id: <20180130083006.GB1245@in.ibm.com>
Date:   Tue, 30 Jan 2018 14:00:06 +0530
From:   Bharata B Rao <bharata@...ux.vnet.ibm.com>
To:     linux-kernel@...r.kernel.org, linux-mm@...ck.org
Cc:     pasha.tatashin@...cle.com
Subject: Memory hotplug not increasing the total RAM

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.

The step 2 has been introduced recently by the following commit:

commit f7f99100d8d95dbcf09e0216a143211e79418b9f
Author: Pavel Tatashin <pasha.tatashin@...cle.com>
Date:   Wed Nov 15 17:36:44 2017 -0800

    mm: stop zeroing memory during allocation in vmemmap

Reverting this commit restores the correct behaviour of memory hotplug.

Regards,
Bharata.