linux-kernel - Re: [PATCH 21/46] hugetlb: use struct hugetlb_pte for walk_hugetlb

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Message-ID: <Y8B8mW2zSWDDwp7G@x1n>
Date:   Thu, 12 Jan 2023 16:33:13 -0500
From:   Peter Xu <peterx@...hat.com>
To:     James Houghton <jthoughton@...gle.com>
Cc:     Mike Kravetz <mike.kravetz@...cle.com>,
        Muchun Song <songmuchun@...edance.com>,
        David Hildenbrand <david@...hat.com>,
        David Rientjes <rientjes@...gle.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Mina Almasry <almasrymina@...gle.com>,
        Zach O'Keefe <zokeefe@...gle.com>,
        Manish Mishra <manish.mishra@...anix.com>,
        Naoya Horiguchi <naoya.horiguchi@....com>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Baolin Wang <baolin.wang@...ux.alibaba.com>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Yang Shi <shy828301@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 21/46] hugetlb: use struct hugetlb_pte for
 walk_hugetlb_range

On Thu, Jan 12, 2023 at 04:17:52PM -0500, James Houghton wrote:
> I'll look into it, but doing it this way will use _mapcount, so we
> won't be able to use the vmemmap optimization. I think even if we do
> use Hugh's approach, refcount is still being kept on the head page, so
> there's still an overflow risk there (but maybe I am
> misunderstanding).

Could you remind me what's the issue if using refcount on the small pages
rather than the head (assuming vmemmap still can be disabled)?

Thanks,

-- 
Peter Xu