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From:   Zi Yan <ziy@nvidia.com>
To:     Matthew Wilcox <willy@infradead.org>
Cc:     Naoya Horiguchi <naoya.horiguchi@linux.dev>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Michal Hocko <mhocko@kernel.org>,
        Naoya Horiguchi <naoya.horiguchi@nec.com>
Subject: Re: v5.18-rc1: migratepages triggers VM_BUG_ON_FOLIO(folio_nr_pages(old) != nr_pages)
Date:   Mon, 04 Apr 2022 12:41:04 -0400
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On 4 Apr 2022, at 12:06, Matthew Wilcox wrote:

> On Mon, Apr 04, 2022 at 11:44:39AM -0400, Zi Yan wrote:
>> I am wondering if my change is the right fix or not. folios with order>0
>> are still available when CONFIG_TRANSPARENT_HUGEPAGE is not set, right?
>
> That's the eventual plan, but it's not possible today.  We need to
> be able to split large folios (eg in truncation) and that functionality
> is still under CONFIG_TRANSPARENT_HUGEPAGE in mm/huge_memory.c.  So
> large folios depend on CONFIG_TRANSPARENT_HUGEPAGE instead of having a
> clean separation between functionality-to-support-PMD-mapping and
> functionality-to-support-order>0.
>
> So I preferred your earlier patch because it's more obvious.  I mean,
> we could pull in the two or three patches from my tree that convert
> these functions and their callers to folios ... we're only at rc1.
> I can post them and see what others think.

OK, I will send out my initial patch.

--
Best Regards,
Yan, Zi

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