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Date:   Thu, 15 Dec 2022 13:45:08 -0500
From:   Peter Xu <peterx@redhat.com>
To:     James Houghton <jthoughton@google.com>
Cc:     Mike Kravetz <mike.kravetz@oracle.com>,
        Muchun Song <songmuchun@bytedance.com>,
        David Hildenbrand <david@redhat.com>,
        David Rientjes <rientjes@google.com>,
        Axel Rasmussen <axelrasmussen@google.com>,
        Mina Almasry <almasrymina@google.com>,
        Zach O'Keefe <zokeefe@google.com>,
        Manish Mishra <manish.mishra@nutanix.com>,
        Naoya Horiguchi <naoya.horiguchi@nec.com>,
        "Dr . David Alan Gilbert" <dgilbert@redhat.com>,
        "Matthew Wilcox (Oracle)" <willy@infradead.org>,
        Vlastimil Babka <vbabka@suse.cz>,
        Baolin Wang <baolin.wang@linux.alibaba.com>,
        Miaohe Lin <linmiaohe@huawei.com>,
        Yang Shi <shy828301@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH v2 24/47] hugetlb: update page_vma_mapped to do
 high-granularity walks
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References: <20221021163703.3218176-1-jthoughton@google.com>
 <20221021163703.3218176-25-jthoughton@google.com>
 <CADrL8HU=39e8ZJkmnXNKrMM=f-v1T+SF1yykC9KzwAi6T+MA4w@mail.gmail.com>
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Hi, James,

On Thu, Dec 15, 2022 at 12:49:18PM -0500, James Houghton wrote:
> > @@ -166,19 +167,57 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)

[...]

> I realize that I can't do this -- we're already holding the
> i_mmap_rwsem, and we have to take the VMA lock first. It seems like
> we're always holding it for writing in this case, so if I make
> hugetlb_collapse taking the i_mmap_rwsem for reading, this will be
> safe.
> 
> Peter, you looked at this recently [1] -- do you know if we're always
> holding i_mmap_rwsem *for writing* here?
> 
> [1] https://lore.kernel.org/linux-mm/20221209170100.973970-10-peterx@redhat.com/

I think so, an analysis is in previous v2 in one of my reply to John:

https://lore.kernel.org/all/Y5JjTPTxCWSklCan@x1n/

No hurt to double check, though.

-- 
Peter Xu