Re: [PATCH v2 0/9] drm/i915: Replace kmap_atomic() with kmap_local_page()

["Fabio M. De Francesco" <fmdefrancesco@gmail.com>]

On mercoledì 29 marzo 2023 09:32:11 CEST Zhao Liu wrote:
> From: Zhao Liu <zhao1.liu@intel.com>
> 
> Hi list,
> 
> Sorry for a long delay since v1 [1]. This patchset is based on 197b6b6
> (Linux 6.3-rc4).
> 
> Welcome and thanks for your review and comments!
> 
> 
> # Purpose of this patchset
> 
> The purpose of this pacthset is to replace all uses of kmap_atomic() in
> i915 with kmap_local_page() because the use of kmap_atomic() is being
> deprecated in favor of kmap_local_page()[1]. And 92b64bd (mm/highmem:
> add notes about conversions from kmap{,_atomic}()) has declared the
> deprecation of kmap_atomic().
> 
> 
> # Motivation for deprecating kmap_atomic() and using kmap_local_page()
> 
> The main difference between atomic and local mappings is that local
> mappings doesn't disable page faults or preemption (the preemption is
> disabled for !PREEMPT_RT case, otherwise it only disables migration).
> 
> With kmap_local_page(), we can avoid the often unwanted side effect of
> unnecessary page faults and preemption disables.
> 
> 
> # Patch summary
> 
> Patch 1, 4-6 and 8-9 replace kamp_atomic()/kunmap_atomic() with
>         kmap_local_page()/kunmap_local() directly. With thses local
>         mappings, the page faults and preemption are allowed.
> 
> Patch 2 and 7 use memcpy_from_page() and memcpy_to_page() to replace
>         kamp_atomic()/kunmap_atomic(). These two variants of memcpy()
>         are based on the local mapping, so page faults and preemption
>         are also allowed in these two interfaces.
> 
> Patch 3 replaces kamp_atomic()/kunmap_atomic() with kmap_local_page()/
>         kunmap_local() and also diable page fault since the for special
>         handling (pls see the commit message).
> 
> 
> # Changes since v1
> 
> * Dropped hot plug related description in commit message since it has
>   nothing to do with kmap_local_page().
> * Emphasized the motivation for using kmap_local_page() in commit
>   message.
> * Rebased patch 1 on f47e630 (drm/i915/gem: Typecheck page lookups) to
>   keep the "idx" variable of type pgoff_t here.
> * Used memcpy_from_page() and memcpy_to_page() to replace
>   kmap_local_page() + memcpy() in patch 2.
> 
> 
> # Reference
> 
> [1]:
> https://lore.kernel.org/lkml/20221017093726.2070674-1-zhao1.liu@linux.intel.c
> om/ [1]:
> https://lore.kernel.org/all/20220813220034.806698-1-ira.weiny@intel.com ---
> Zhao Liu (9):
>   drm/i915: Use kmap_local_page() in gem/i915_gem_object.c
>   drm/i915: Use memcpy_[from/to]_page() in gem/i915_gem_pyhs.c
>   drm/i915: Use kmap_local_page() in gem/i915_gem_shmem.c
>   drm/i915: Use kmap_local_page() in gem/selftests/huge_pages.c
>   drm/i915: Use kmap_local_page() in gem/selftests/i915_gem_coherency.c
>   drm/i915: Use kmap_local_page() in gem/selftests/i915_gem_context.c
>   drm/i915: Use memcpy_from_page() in gt/uc/intel_uc_fw.c
>   drm/i915: Use kmap_local_page() in i915_cmd_parser.c
>   drm/i915: Use kmap_local_page() in gem/i915_gem_execbuffer.c
> 

I _think_ that the "long delay" you mentioned in the first sentence has paid 
off in full. 

I don't see things to improve (except all those "kamp_atomic()" typo in the 
patches summary; however, typos are only in the cover so I'm sure they won't 
hurt anybody). 

Each of the nine patches listed above looks good to me, so they are all…

Reviewed-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>

Thanks!

Fabio

PS: Obviously there was no need to reconfirm my tag for patch 3/9. A single 
tag that catches all patches is easier for a lazy person like me :-)

>
>  drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c       | 10 +++++-----
>  drivers/gpu/drm/i915/gem/i915_gem_object.c           |  8 +++-----
>  drivers/gpu/drm/i915/gem/i915_gem_phys.c             | 10 ++--------
>  drivers/gpu/drm/i915/gem/i915_gem_shmem.c            |  6 ++++--
>  drivers/gpu/drm/i915/gem/selftests/huge_pages.c      |  6 +++---
>  .../gpu/drm/i915/gem/selftests/i915_gem_coherency.c  | 12 ++++--------
>  .../gpu/drm/i915/gem/selftests/i915_gem_context.c    |  8 ++++----
>  drivers/gpu/drm/i915/gt/uc/intel_uc_fw.c             |  5 +----
>  drivers/gpu/drm/i915/i915_cmd_parser.c               |  4 ++--
>  9 files changed, 28 insertions(+), 41 deletions(-)
> 
> --
> 2.34.1