linux-kernel - Re: [RFC PATCH v2 16/47] hugetlb: make unmapping compatible with high-granularity mappings

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Date:   Wed, 14 Dec 2022 16:28:56 -0800
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     James Houghton <jthoughton@...gle.com>
Cc:     Muchun Song <songmuchun@...edance.com>,
        Peter Xu <peterx@...hat.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: [RFC PATCH v2 16/47] hugetlb: make unmapping compatible with
 high-granularity mappings

On 10/21/22 16:36, James Houghton wrote:
> Enlighten __unmap_hugepage_range to deal with high-granularity mappings.
> This doesn't change its API; it still must be called with hugepage
> alignment, but it will correctly unmap hugepages that have been mapped
> at high granularity.
> 
> The rules for mapcount and refcount here are:
>  1. Refcount and mapcount are tracked on the head page.
>  2. Each page table mapping into some of an hpage will increase that
>     hpage's mapcount and refcount by 1.
> 
> Eventually, functionality here can be expanded to allow users to call
> MADV_DONTNEED on PAGE_SIZE-aligned sections of a hugepage, but that is
> not done here.
> 
> Signed-off-by: James Houghton <jthoughton@...gle.com>
> ---
>  include/asm-generic/tlb.h |  6 ++--
>  mm/hugetlb.c              | 76 +++++++++++++++++++++++++--------------
>  2 files changed, 52 insertions(+), 30 deletions(-)

All looks reasonable, nothing stands out.

-- 
Mike Kravetz