linux-kernel - Re: [PATCH v4 0/6] mm/migrate: avoid device private invalidations

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Date:   Tue, 28 Jul 2020 16:22:36 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Ralph Campbell <rcampbell@...dia.com>
CC:     <linux-rdma@...r.kernel.org>, <linux-mm@...ck.org>,
        <nouveau@...ts.freedesktop.org>, <kvm-ppc@...r.kernel.org>,
        <linux-kselftest@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        Jerome Glisse <jglisse@...hat.com>,
        John Hubbard <jhubbard@...dia.com>,
        Christoph Hellwig <hch@....de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Shuah Khan <shuah@...nel.org>, Ben Skeggs <bskeggs@...hat.com>,
        Bharata B Rao <bharata@...ux.ibm.com>
Subject: Re: [PATCH v4 0/6] mm/migrate: avoid device private invalidations

On Thu, Jul 23, 2020 at 03:29:58PM -0700, Ralph Campbell wrote:
> The goal for this series is to avoid device private memory TLB
> invalidations when migrating a range of addresses from system
> memory to device private memory and some of those pages have already
> been migrated. The approach taken is to introduce a new mmu notifier
> invalidation event type and use that in the device driver to skip
> invalidation callbacks from migrate_vma_setup(). The device driver is
> also then expected to handle device MMU invalidations as part of the
> migrate_vma_setup(), migrate_vma_pages(), migrate_vma_finalize() process.
> Note that this is opt-in. A device driver can simply invalidate its MMU
> in the mmu notifier callback and not handle MMU invalidations in the
> migration sequence.
> 
> This series is based on Jason Gunthorpe's HMM tree (linux-5.8.0-rc4).
> 
> Also, this replaces the need for the following two patches I sent:
> ("mm: fix migrate_vma_setup() src_owner and normal pages")
> https://lore.kernel.org/linux-mm/20200622222008.9971-1-rcampbell@nvidia.com
> ("nouveau: fix mixed normal and device private page migration")
> https://lore.kernel.org/lkml/20200622233854.10889-3-rcampbell@nvidia.com
> 
> Changes in v4:
> Added reviewed-by from Bharata B Rao.
> Removed dead code checking for source device private page in lib/test_hmm.c
>   dmirror_migrate_alloc_and_copy() since the source filter flag guarantees
>   that.
> Added patch 6 to remove a redundant invalidation in migrate_vma_pages().
> 
> Changes in v3:
> Changed the direction field "dir" to a "flags" field and renamed
>   src_owner to pgmap_owner.
> Fixed a locking issue in nouveau for the migration invalidation.
> Added a HMM selftest test case to exercise the HMM test driver
>   invalidation changes.
> Removed reviewed-by Bharata B Rao since this version is moderately
>   changed.
> 
> Changes in v2:
> Rebase to Jason Gunthorpe's HMM tree.
> Added reviewed-by from Bharata B Rao.
> Rename the mmu_notifier_range::data field to migrate_pgmap_owner as
>   suggested by Jason Gunthorpe.
> 
> Ralph Campbell (6):
>   nouveau: fix storing invalid ptes
>   mm/migrate: add a flags parameter to migrate_vma
>   mm/notifier: add migration invalidation type
>   nouveau/svm: use the new migration invalidation
>   mm/hmm/test: use the new migration invalidation

Applied to the hmm tree with the modification I noted, I think all the
comments in the past versions were addressed. I will accumulate more
Reviews if any come.

>   mm/migrate: remove range invalidation in migrate_vma_pages()

Let's have some discussion on this new patch please, at least I don't
follow it yet.

Thanks,
Jason