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

[Zhao Liu]

Hi Fabio,

On Wed, Mar 29, 2023 at 06:03:38PM +0200, Fabio M. De Francesco wrote:
> Date: Wed, 29 Mar 2023 18:03:38 +0200
> From: "Fabio M. De Francesco" <fmdefrancesco@xxxxxxxxx>
> Subject: Re: [PATCH v2 0/9] drm/i915: Replace kmap_atomic() with
>  kmap_local_page()
> 
> On mercoledì 29 marzo 2023 09:32:11 CEST Zhao Liu wrote:
> > From: Zhao Liu <zhao1.liu@xxxxxxxxx>
> > 
> > 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@xxxxxxxxx ---
> > 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). 

Thanks a lot for your patience and your help! :-)

> 
> Each of the nine patches listed above looks good to me, so they are all…
> 
> Reviewed-by: Fabio M. De Francesco <fmdefrancesco@xxxxxxxxx>
> 
> 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 :-)

The typos and this description still can be improved. I'll pay
attention in the future!

Thanks,
Zhao

> 
> >
> >  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
> 
> 
> 
>