linux-kernel - Re: [PATCH v6 0/8] mmu notifier provide context informations

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Date:   Tue, 9 Apr 2019 15:08:55 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     jglisse@...hat.com
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Christian König <christian.koenig@....com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>, Jan Kara <jack@...e.cz>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Peter Xu <peterx@...hat.com>,
        Felix Kuehling <Felix.Kuehling@....com>,
        Jason Gunthorpe <jgg@...lanox.com>,
        Ross Zwisler <zwisler@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Alex Deucher <alexander.deucher@....com>,
        Radim Krčmář 
        <rkrcmar@...hat.com>, Michal Hocko <mhocko@...nel.org>,
        Ben Skeggs <bskeggs@...hat.com>,
        Ralph Campbell <rcampbell@...dia.com>,
        John Hubbard <jhubbard@...dia.com>, kvm@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linux-rdma@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v6 0/8] mmu notifier provide context informations

On Tue, 26 Mar 2019 12:47:39 -0400 jglisse@...hat.com wrote:

> From: Jérôme Glisse <jglisse@...hat.com>
> 
> (Andrew this apply on top of my HMM patchset as otherwise you will have
>  conflict with changes to mm/hmm.c)
> 
> Changes since v5:
>     - drop KVM bits waiting for KVM people to express interest if they
>       do not then i will post patchset to remove change_pte_notify as
>       without the changes in v5 change_pte_notify is just useless (it
>       it is useless today upstream it is just wasting cpu cycles)
>     - rebase on top of lastest Linus tree
> 
> Previous cover letter with minor update:
> 
> 
> Here i am not posting users of this, they already have been posted to
> appropriate mailing list [6] and will be merge through the appropriate
> tree once this patchset is upstream.
> 
> Note that this serie does not change any behavior for any existing
> code. It just pass down more information to mmu notifier listener.
> 
> The rational for this patchset:
> 
> CPU page table update can happens for many reasons, not only as a
> result of a syscall (munmap(), mprotect(), mremap(), madvise(), ...)
> but also as a result of kernel activities (memory compression, reclaim,
> migration, ...).
> 
> This patch introduce a set of enums that can be associated with each
> of the events triggering a mmu notifier:
> 
>     - UNMAP: munmap() or mremap()
>     - CLEAR: page table is cleared (migration, compaction, reclaim, ...)
>     - PROTECTION_VMA: change in access protections for the range
>     - PROTECTION_PAGE: change in access protections for page in the range
>     - SOFT_DIRTY: soft dirtyness tracking
> 
> Being able to identify munmap() and mremap() from other reasons why the
> page table is cleared is important to allow user of mmu notifier to
> update their own internal tracking structure accordingly (on munmap or
> mremap it is not longer needed to track range of virtual address as it
> becomes invalid). Without this serie, driver are force to assume that
> every notification is an munmap which triggers useless trashing within
> drivers that associate structure with range of virtual address. Each
> driver is force to free up its tracking structure and then restore it
> on next device page fault. With this serie we can also optimize device
> page table update [6].
> 
> More over this can also be use to optimize out some page table updates
> like for KVM where we can update the secondary MMU directly from the
> callback instead of clearing it.

We seem to be rather short of review input on this patchset.  ie: there
is none.

> ACKS AMD/RADEON https://lkml.org/lkml/2019/2/1/395

OK, kind of ackish, but not a review.

> ACKS RDMA https://lkml.org/lkml/2018/12/6/1473

This actually acks the infiniband part of a patch which isn't in this
series.


So we have some work to do, please.  Who would be suitable reviewers?