Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::3:6 as permitted sender) client-ip=2620:137:e000::3:6;
MIME-Version: 1.0
References: <ZSlragGjFEw9QS1Y@x1n> <12588295-2616-eb11-43d2-96a3c62bd181@redhat.com>
 <ZS2IjEP479WtVdMi@x1n> <8d187891-f131-4912-82d8-13112125b210@redhat.com>
 <ZS7ZqztMbhrG52JQ@x1n> <d40b8c86-6163-4529-ada4-d2b3c1065cba@redhat.com>
 <ZTGJHesvkV84c+l6@x1n> <81cf0943-e258-494c-812a-0c00b11cf807@redhat.com>
 <CAJuCfpHZWfjW530CvQCFx-PYNSaeQwkh-+Z6KgdfFyZHRGSEDQ@mail.gmail.com>
 <d34dfe82-3e31-4f85-8405-c582a0650688@redhat.com> <ZTVD18RgBfITsQC4@x1n>
 <1156ad46-1952-4892-8092-bfbb8588c3f3@redhat.com> <96899aa6-700b-41b9-ab11-2cae48d75549@redhat.com>
In-Reply-To: <96899aa6-700b-41b9-ab11-2cae48d75549@redhat.com>
From:   Suren Baghdasaryan <surenb@google.com>
Date:   Mon, 23 Oct 2023 10:33:40 -0700
Message-ID: <CAJuCfpF+ADAG=vn4y0EKo29j5zUx-TG=puF7Bq8oSp1_7T+OSw@mail.gmail.com>
Subject: Re: [PATCH v3 2/3] userfaultfd: UFFDIO_MOVE uABI
To:     David Hildenbrand <david@redhat.com>
Cc:     Peter Xu <peterx@redhat.com>,
        Lokesh Gidra <lokeshgidra@google.com>,
        akpm@linux-foundation.org, viro@zeniv.linux.org.uk,
        brauner@kernel.org, shuah@kernel.org, aarcange@redhat.com,
        hughd@google.com, mhocko@suse.com, axelrasmussen@google.com,
        rppt@kernel.org, willy@infradead.org, Liam.Howlett@oracle.com,
        jannh@google.com, zhangpeng362@huawei.com, bgeffon@google.com,
        kaleshsingh@google.com, ngeoffray@google.com, jdduke@google.com,
        linux-mm@kvack.org, linux-fsdevel@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org,
        kernel-team@android.com
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On Mon, Oct 23, 2023 at 9:36=E2=80=AFAM David Hildenbrand <david@redhat.com=
> wrote:
>
> On 23.10.23 14:03, David Hildenbrand wrote:
> > On 22.10.23 17:46, Peter Xu wrote:
> >> On Fri, Oct 20, 2023 at 07:16:19PM +0200, David Hildenbrand wrote:
> >>> These are rather the vibes I'm getting from Peter. "Why rename it, co=
uld
> >>> confuse people because the original patches are old", "Why exclude it=
 if it
> >>> has been included in the original patches". Not the kind of reasoning=
 I can
> >>> relate to when it comes to upstreaming some patches.
> >>
> >> You can't blame anyone if you misunderstood and biased the question.
> >>
> >> The first question is definitely valid, even until now.  You guys stil=
l
> >> prefer to rename it, which I'm totally fine with.
> >>
> >> The 2nd question is wrong from your interpretation.  That's not my poi=
nt,
> >> at least not starting from a few replies already.  What I was asking f=
or is
> >> why such page movement between mm is dangerous.  I don't think I get s=
olid
> >> answers even until now.
> >>
> >> Noticing "memcg is missing" is not an argument for "cross-mm is danger=
ous",
> >> it's a review comment.  Suren can address that.
> >>
> >> You'll propose a new feature that may tag an mm is not an argument eit=
her,
> >> if it's not merged yet.  We can also address that depending on what it=
 is,
> >> also on which lands earlier.
> >>
> >> It'll be good to discuss these details even in a single-mm support.  A=
nyone
> >> would like to add that can already refer to discussion in this thread.
> >>
> >> I hope I'm clear.
> >>
> >
> > I said everything I had to say, go read what I wrote.
>
> Re-read your message after flying over first couple of paragraphs
> previously a bit quick too quickly (can easily happen when I'm told that
> I misunderstand questions and read them in a "biased" way).
>
> I'll happy to discuss cross-mm support once we actually need it. I just
> don't see the need to spend any energy on that right now, without any
> users on the horizon.
>
> [(a) I didn't blame anybody, I said that I don't understand the
> reasoning. (b) I hope I made it clear that this is added complexity (and
> not just currently dangerous) and so far I haven't heard a compelling
> argument why we should do any of that or even spend our time discussing
> that. (c) I never used "memcg is missing" as an argument for "cross-mm
> is dangerous", all about added complexity without actual users. (d) "it
> easily shows that there are cases  where this will require extra work --
> without any current benefits" -- is IMHO a perfectly fine argument
> against complexity that currently nobody needs]

Thanks for the discussion, folks!
I think posting the single-mm first and then following up with
cross-mm and its test would help us move forward. That will provide
functionality that is needed today quickly without unnecessary
distractions and will give us more time to discuss cross-mm support.
Also we will be able to test single-mm in isolation and make it more
solid before moving onto cross-mm.
I'll try to post the next version sometime this week.
Thanks,
Suren.

>
> --
> Cheers,
>
> David / dhildenb
>