linux-kernel - Re: [PATCH] mm: migrate: fix an incorrect call of prep_transhuge

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Message-Id: <20171121141213.89db86bfbd75c22fc0209990@linux-foundation.org>
Date:   Tue, 21 Nov 2017 14:12:13 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Zi Yan <zi.yan@...t.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Zi Yan <zi.yan@...rutgers.edu>,
        Andrea Reale <ar@...ux.vnet.ibm.com>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        stable@...r.kernel.org
Subject: Re: [PATCH] mm: migrate: fix an incorrect call of
 prep_transhuge_page()

On Mon, 20 Nov 2017 21:18:55 -0500 Zi Yan <zi.yan@...t.com> wrote:

> In [1], Andrea reported that during memory hotplug/hot remove
> prep_transhuge_page() is called incorrectly on non-THP pages for
> migration, when THP is on but THP migration is not enabled.
> This leads to a bad state of target pages for migration.
> 
> This patch fixes it by only calling prep_transhuge_page() when we are
> certain that the target page is THP.

What are the user-visible effects of the bug?