linux-kernel - Re: [PATCH RFC 0/5] mm/gup: Introduce exclusive GUP pinning

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Date: Fri, 21 Jun 2024 09:54:12 +0100
From: Fuad Tabba <tabba@...gle.com>
To: David Hildenbrand <david@...hat.com>
Cc: Sean Christopherson <seanjc@...gle.com>, Jason Gunthorpe <jgg@...dia.com>, 
	John Hubbard <jhubbard@...dia.com>, Elliot Berman <quic_eberman@...cinc.com>, 
	Andrew Morton <akpm@...ux-foundation.org>, Shuah Khan <shuah@...nel.org>, 
	Matthew Wilcox <willy@...radead.org>, maz@...nel.org, kvm@...r.kernel.org, 
	linux-arm-msm@...r.kernel.org, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org, 
	pbonzini@...hat.com
Subject: Re: [PATCH RFC 0/5] mm/gup: Introduce exclusive GUP pinning

Hi David,

On Fri, Jun 21, 2024 at 9:44 AM David Hildenbrand <david@...hat.com> wrote:
>
> >> Again from that thread, one of most important aspects guest_memfd is that VMAs
> >> are not required.  Stating the obvious, lack of VMAs makes it really hard to drive
> >> swap, reclaim, migration, etc. from code that fundamentally operates on VMAs.
> >>
> >>   : More broadly, no VMAs are required.  The lack of stage-1 page tables are nice to
> >>   : have; the lack of VMAs means that guest_memfd isn't playing second fiddle, e.g.
> >>   : it's not subject to VMA protections, isn't restricted to host mapping size, etc.
> >>
> >> [1] https://lore.kernel.org/all/Zfmpby6i3PfBEcCV@google.com
> >> [2] https://lore.kernel.org/all/Zg3xF7dTtx6hbmZj@google.com
> >
> > I wonder if it might be more productive to also discuss this in one of
> > the PUCKs, ahead of LPC, in addition to trying to go over this in LPC.
>
> I don't know in  which context you usually discuss that, but I could
> propose that as a topic in the bi-weekly MM meeting.
>
> This would, of course, be focused on the bigger MM picture: how to mmap,
> how how to support huge pages, interaction with page pinning, ... So
> obviously more MM focused once we are in agreement that we want to
> support shared memory in guest_memfd and how to make that work with core-mm.
>
> Discussing if we want shared memory in guest_memfd might be betetr
> suited for a different, more CC/KVM specific meeting (likely the "PUCKs"
> mentioned here?).

Sorry, I should have given more context on what a PUCK* is :) It's a
periodic (almost weekly) upstream call for KVM.

[*] https://lore.kernel.org/all/20230512231026.799267-1-seanjc@google.com/

But yes, having a discussion in one of the mm meetings ahead of LPC
would also be great. When do these meetings usually take place, to try
to coordinate across timezones.

Cheers,
/fuad

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