linux-kernel - Re: [PATCH v2 05/46] rmap: hugetlb: switch from page_dup_file_rmap to page_add_file

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Message-ID: <20230302192252.GA10997@monkey>
Date:   Thu, 2 Mar 2023 11:22:52 -0800
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     James Houghton <jthoughton@...gle.com>
Cc:     Jiaqi Yan <jiaqiyan@...gle.com>,
        Muchun Song <songmuchun@...edance.com>,
        Peter Xu <peterx@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        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>,
        Frank van der Linden <fvdl@...gle.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 05/46] rmap: hugetlb: switch from page_dup_file_rmap
 to page_add_file_rmap

On 03/02/23 08:43, James Houghton wrote:
> 
> This solution limits the size of a HugeTLB page to 16G. I'm not sure
> if there are any architectures that support HugeTLB pages larger than
> 16G (it looks like powerpc supports 16G). If they do, I think we can
> just increase the value of COMPOUND_MAPPED. If that's not possible, we
> would need another solution than participating in _nr_pages_mapped
> like THPs.

For now, I believe you should continue with the THP like approach.

A couple days back, Matthew asked me to take a look and comment on his
latest mapcount proposal.  I have not done that yet. :( The hope is that
this will make hugetlb HGM simpler as well.

It is somewhat troubling that mapcount may be changed in the near future.
Better to be consistent with THP than invent something hugetlb HGM specific.
That way, when THP is updated hugetlb updates should be nearly the same.
-- 
Mike Kravetz