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Date:   Tue, 6 Jun 2023 22:15:38 +0200
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Subject: Re: RFC for new feature to move pages from one vma to another without
 split
To:     Peter Xu <peterx@redhat.com>, David Hildenbrand <david@redhat.com>
Cc:     Lokesh Gidra <lokeshgidra@google.com>,
        Axel Rasmussen <axelrasmussen@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        "open list:MEMORY MANAGEMENT" <linux-mm@kvack.org>,
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        "Kirill A . Shutemov" <kirill@shutemov.name>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Brian Geffon <bgeffon@google.com>,
        Suren Baghdasaryan <surenb@google.com>,
        Kalesh Singh <kaleshsingh@google.com>,
        Nicolas Geoffray <ngeoffray@google.com>,
        Jared Duke <jdduke@google.com>,
        android-mm <android-mm@google.com>,
        Blake Caldwell <blake.caldwell@colorado.edu>,
        Mike Rapoport <rppt@kernel.org>
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On 4/13/23 17:36, Peter Xu wrote:
> On Thu, Apr 13, 2023 at 10:10:44AM +0200, David Hildenbrand wrote:
>> So instead, we consider the whole address space as a virtual, anon file,
>> starting at offset 0. The pgoff of a VMA is then simply the offset in that
>> virtual file (easily computed from the start of the VMA), and VMA merging is
>> just the same as for an ordinary file.
> 
> Interesting point, thanks!

FYI, I've advised a master thesis exploring how to update page->index during
mremap() to keep things mergeable:

https://dspace.cuni.cz/bitstream/handle/20.500.11956/176288/120426800.pdf

I think the last RFC posting was:
https://lore.kernel.org/all/20220516125405.1675-1-matenajakub@gmail.com/

It was really tricky for the general case. Maybe it would be more feasible
for the limited case Lokesh describes, if we could be sure the pages that
are moved aren't mapped anywhere else.