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Date:   Mon, 11 Apr 2022 20:08:00 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Dave Hansen <dave.hansen@intel.com>
Cc:     Khalid Aziz <khalid.aziz@oracle.com>, akpm@linux-foundation.org,
        aneesh.kumar@linux.ibm.com, arnd@arndb.de, 21cnbao@gmail.com,
        corbet@lwn.net, dave.hansen@linux.intel.com, david@redhat.com,
        ebiederm@xmission.com, hagen@jauu.net, jack@suse.cz,
        keescook@chromium.org, kirill@shutemov.name, kucharsk@gmail.com,
        linkinjeon@kernel.org, linux-fsdevel@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        longpeng2@huawei.com, luto@kernel.org, markhemm@googlemail.com,
        pcc@google.com, rppt@kernel.org, sieberf@amazon.com,
        sjpark@amazon.de, surenb@google.com, tst@schoebel-theuer.de,
        yzaikin@google.com
Subject: Re: [PATCH v1 00/14] Add support for shared PTEs across processes
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On Mon, Apr 11, 2022 at 11:51:46AM -0700, Dave Hansen wrote:
> On 4/11/22 10:37, Matthew Wilcox wrote:
> > Another argument that MM developers find compelling is that we can reduce
> > some of the complexity in hugetlbfs where it has the ability to share
> > page tables between processes.
> 
> When could this complexity reduction actually happen in practice?  Can
> this mshare thingy be somehow dropped in underneath the existing
> hugetlbfs implementation?  Or would userspace need to change?

Userspace needs to opt in to mshare, so there's going to be a transition
period where we still need hugetlbfs to still support it, but I have
the impression that the users that need page table sharing are pretty
specialised and we'll be able to find them all before disabling it.

I don't think we can make it transparent to userspace, but I'll noodle
on that a bit.