linux-kernel - Re: [PATCH v4 0/1] Use HMM for ODP v4

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Message-ID: <20190523173302.GD5104@redhat.com>
Date:   Thu, 23 May 2019 13:33:03 -0400
From:   Jerome Glisse <jglisse@...hat.com>
To:     Jason Gunthorpe <jgg@...pe.ca>
Cc:     linux-kernel@...r.kernel.org, linux-rdma@...r.kernel.org,
        Leon Romanovsky <leonro@...lanox.com>,
        Doug Ledford <dledford@...hat.com>,
        Artemy Kovalyov <artemyko@...lanox.com>,
        Moni Shoua <monis@...lanox.com>,
        Mike Marciniszyn <mike.marciniszyn@...el.com>,
        Kaike Wan <kaike.wan@...el.com>,
        Dennis Dalessandro <dennis.dalessandro@...el.com>
Subject: Re: [PATCH v4 0/1] Use HMM for ODP v4

On Thu, May 23, 2019 at 01:34:29PM -0300, Jason Gunthorpe wrote:
> On Thu, May 23, 2019 at 11:52:08AM -0400, Jerome Glisse wrote:
> > On Thu, May 23, 2019 at 12:41:49PM -0300, Jason Gunthorpe wrote:
> > > On Thu, May 23, 2019 at 11:04:32AM -0400, Jerome Glisse wrote:
> > > > On Wed, May 22, 2019 at 08:57:37PM -0300, Jason Gunthorpe wrote:
> > > > > On Wed, May 22, 2019 at 01:48:52PM -0400, Jerome Glisse wrote:
> > > > > 
> > > > > > > > So attached is a rebase on top of 5.2-rc1, i have tested with pingpong
> > > > > > > > (prefetch and not and different sizes). Seems to work ok.
> > > > > > > 
> > > > > > > Urk, it already doesn't apply to the rdma tree :(
> > > > > > > 
> > > > > > > The conflicts are a little more extensive than I'd prefer to handle..
> > > > > > > Can I ask you to rebase it on top of this branch please:
> > > > > > > 
> > > > > > > https://git.kernel.org/pub/scm/linux/kernel/git/rdma/rdma.git/log/?h=wip/jgg-for-next
> > > > > > > 
> > > > > > > Specifically it conflicts with this patch:
> > > > > > > 
> > > > > > > https://git.kernel.org/pub/scm/linux/kernel/git/rdma/rdma.git/commit/?h=wip/jgg-for-next&id=d2183c6f1958e6b6dfdde279f4cee04280710e34
> > > > > 
> > > > > There is at least one more serious blocker here:
> > > > > 
> > > > > config ARCH_HAS_HMM_MIRROR
> > > > >         bool
> > > > >         default y
> > > > >         depends on (X86_64 || PPC64)
> > > > >         depends on MMU && 64BIT
> > > > > 
> > > > > I can't loose ARM64 support for ODP by merging this, that is too
> > > > > serious of a regression.
> > > > > 
> > > > > Can you fix it?
> > > > 
> > > > 5.2 already has patch to fix the Kconfig (ARCH_HAS_HMM_MIRROR and
> > > > ARCH_HAS_HMM_DEVICE replacing ARCH_HAS_HMM) I need to update nouveau
> > > 
> > > Newer than 5.2-rc1? Is this why ARCH_HAS_HMM_MIRROR is not used anywhere?
> > 
> > Yes this is multi-step update, first add the new Kconfig release n,
> > update driver in release n+1, update core Kconfig in release n+2
> > 
> > So we are in release n (5.2), in 5.3 i will update nouveau and amdgpu
> > so that in 5.4 in ca remove the old ARCH_HAS_HMM
> 
> Why don't you just send the patch for both parts to mm or to DRM?
> 
> This is very normal - as long as the resulting conflicts would be
> small during there is no reason not to do this. Can you share the
> combined patch?

This was tested in the past an resulted in failure. So for now i am
taking the simplest and easiest path with the least burden for every
maintainer. It only complexify my life.

Note that mm is not a git tree and thus i can not play any git trick
to help in this endeavor.

> > > If mm takes the fixup patches so hmm mirror is as reliable as ODP's
> > > existing stuff, and patch from you to enable ARM64, then we can
> > > continue to merge into 5.3
> > > 
> > > So, let us try to get acks on those other threads..
> > 
> > I will be merging your patchset and Ralph and repost, they are only
> > minor change mostly that you can not update the driver API in just
> > one release.
> 
> Of course you can, we do it all the time. It requires some
> co-ordination, but as long as the merge conflicts are not big it is
> fine.
> 
> Merge the driver API change and the call site updates to -mm and
> refain from merging horrendously conflicting patches through DRM.
> 
> In the case of the changes in my HMM RFC it is something like 2
> lines in DRM that need touching, no problem at all.
> 
> If you want help I can volunteer make a hmm PR for Linus just for this
> during the merge window - but Andrew would need to agree and ack the
> patches.

This was tested in the past and i do not want to go over this issue
again (or re-iterate the long emails discussion associated with that).
It failed and it put the burden on every maintainers. So it is easier
to do the multi-step thing.

You can take a peak at Ralph patchset and yours into one with minor
changes here:

https://cgit.freedesktop.org/~glisse/linux/log/?h=hmm-5.3

I am about to start testing it with nouveau, amdgpu and RDMA.

Cheers,
Jérôme