linux-kernel - Re: [RFC PATCH 0/6] Add support for shared PTEs across processes

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Date:   Tue, 25 Jan 2022 13:23:21 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     Khalid Aziz <khalid.aziz@...cle.com>, akpm@...ux-foundation.org,
        longpeng2@...wei.com, arnd@...db.de, dave.hansen@...ux.intel.com,
        david@...hat.com, rppt@...nel.org, surenb@...gle.com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [RFC PATCH 0/6] Add support for shared PTEs across processes

On Tue, Jan 25, 2022 at 02:42:12PM +0300, Kirill A. Shutemov wrote:
> I wounder if we can get away with zero-API here: we can transparently
> create/use shared page tables for any inode on mmap(MAP_SHARED) as long as
> size and alignment is sutiable. Page tables will be linked to the inode
> and will be freed when the last of such mapping will go away. I don't see
> a need in new syscalls of flags to existing one.

That's how HugeTLBfs works today, right?  Would you want that mechanism
hoisted into the real MM?  Because my plan was the opposite -- remove it
from the shadow MM once mshare() is established.