linux-kernel - Re: [PATCH v6 0/8] Emulated coherent graphics memory take 2

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Date:   Mon, 21 Oct 2019 12:24:45 +0000
From:   Thomas Hellstrom <thellstrom@...are.com>
To:     Thomas Hellström (VMware) 
        <thomas_os@...pmail.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>
CC:     "torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>,
        Will Deacon <will.deacon@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Rik van Riel <riel@...riel.com>,
        Minchan Kim <minchan@...nel.org>,
        Michal Hocko <mhocko@...e.com>,
        Huang Ying <ying.huang@...el.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        "Kirill A . Shutemov" <kirill@...temov.name>
Subject: Re: [PATCH v6 0/8] Emulated coherent graphics memory take 2

On 10/14/19 3:22 PM, Thomas Hellström (VMware) wrote:
> From: Thomas Hellström <thellstrom@...are.com>
>
> Graphics APIs like OpenGL 4.4 and Vulkan require the graphics driver
> to provide coherent graphics memory, meaning that the GPU sees any
> content written to the coherent memory on the next GPU operation that
> touches that memory, and the CPU sees any content written by the GPU
> to that memory immediately after any fence object trailing the GPU
> operation is signaled.
>
> Paravirtual drivers that otherwise require explicit synchronization
> needs to do this by hooking up dirty tracking to pagefault handlers
> and buffer object validation.
>
> Provide mm helpers needed for this and that also allow for huge pmd-
> and pud entries (patch 1-3), and the associated vmwgfx code (patch 4-7).
>
> The code has been tested and exercised by a tailored version of mesa
> where we disable all explicit synchronization and assume graphics memory
> is coherent. The performance loss varies of course; a typical number is
> around 5%.
>
> I would like to merge this code through the DRM tree, so an ack to include
> the new mm helpers in that merge would be greatly appreciated.
>
> Changes since RFC:
> - Merge conflict changes moved to the correct patch. Fixes intra-patchset
>   compile errors.
> - Be more aggressive when turning ttm vm code into helpers. This makes sure
>   we can use a const qualifier on the vmwgfx vm_ops.
> - Reinstate a lost comment an fix an error path that was broken when turning
>   the ttm vm code into helpers.
> - Remove explicit type-casts of struct vm_area_struct::vm_private_data
> - Clarify the locking inversion that makes us not being able to use the mm
>   pagewalk code.
>
> Changes since v1:
> - Removed the vmwgfx maintainer entry for as_dirty_helpers.c, updated
>   commit message accordingly
> - Removed the TTM patches from the series as they are merged separately
>   through DRM.
> Changes since v2:
> - Split out the pagewalk code from as_dirty_helpers.c and document locking.
> - Add pre_vma and post_vma callbacks to the pagewalk code.
> - Remove huge pmd and -pud asserts that would trip when we protect vmas with
>   struct address_space::i_mmap_rwsem rather than with
>   struct vm_area_struct::mmap_sem.
> - Do some naming cleanup in as_dirty_helpers.c
> Changes since v3:
> - Extensive renaming of the dirty helpers including the filename.
> - Update walk_page_mapping() doc.
> - Update the pagewalk code to not unconditionally split pmds if a pte_entry()
>   callback is present. Update the dirty helper pmd_entry accordingly.
> - Use separate walk ops for the dirty helpers.
> - Update the pagewalk code to take the pagetable lock in walk_pte_range.
> Changes since v4:
> - Fix pte pointer confusion in patch 2/8
> - Skip the pagewalk code conditional split patch for now, and update the
>   mapping_dirty_helper accordingly. That problem will be solved in a cleaner
>   way in a follow-up patchset.
> Changes since v5:
> - Fix tlb flushing when we have other pending tlb flushes.
>   
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Matthew Wilcox <willy@...radead.org>
> Cc: Will Deacon <will.deacon@....com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Rik van Riel <riel@...riel.com>
> Cc: Minchan Kim <minchan@...nel.org>
> Cc: Michal Hocko <mhocko@...e.com>
> Cc: Huang Ying <ying.huang@...el.com>
> Cc: Jérôme Glisse <jglisse@...hat.com>
> Cc: Kirill A. Shutemov <kirill@...temov.name>
>
Kirill, Linus

I have a formal Ack for two of the four mm patches. Is there a chance I
can get an ack to merge the mm patches of this series through drm with
the vmwgfx patches?

Thanks,

Thomas