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Date:   Mon, 4 Apr 2022 11:28:02 -0700
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Zi Yan <ziy@nvidia.com>
Cc:     Zi Yan <zi.yan@sent.com>, linux-mm@kvack.org,
        Matthew Wilcox <willy@infradead.org>,
        Michal Hocko <mhocko@kernel.org>,
        Naoya Horiguchi <naoya.horiguchi@nec.com>,
        linux-kernel@vger.kernel.org,
        Naoya Horiguchi <naoya.horiguchi@linux.dev>
Subject: Re: [PATCH] mm: migrate: use thp_order instead of HPAGE_PMD_ORDER
 for new page allocation.
Message-Id: <20220404112802.4c07585b7b7e420342c9b0fb@linux-foundation.org>
In-Reply-To: <20220404165325.1883267-1-zi.yan@sent.com>
References: <20220404165325.1883267-1-zi.yan@sent.com>
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On Mon,  4 Apr 2022 12:53:25 -0400 Zi Yan <zi.yan@sent.com> wrote:

> From: Zi Yan <ziy@nvidia.com>
> 
> With folios support, it is possible to have other than HPAGE_PMD_ORDER
> THPs, in the form of folios, in the system. Use thp_order() to correctly
> determine the source page order during migration.

Changelog doesn't describe the end user visible effects of the bug. 
And it really should, because

> Link: https://lore.kernel.org/linux-mm/20220404132908.GA785673@u2004/

it fixes a kernel crash!