linux-kernel - Re: [PATCH v2] drm/i915: Replace kmap() with kmap_local

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Message-ID: <20230619154550.GB412243@sumitra.com>
Date:   Mon, 19 Jun 2023 08:45:50 -0700
From:   Sumitra Sharma <sumitraartsy@...il.com>
To:     Ira Weiny <ira.weiny@...el.com>
Cc:     Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org,
        Thomas Hellström (Intel) 
        <thomas_os@...pmail.org>, Fabio <fmdefrancesco@...il.com>,
        Deepak R Varma <drv@...lo.com>,
        Sumitra Sharma <sumitraartsy@...il.com>
Subject: Re: [PATCH v2] drm/i915: Replace kmap() with kmap_local_page()

On Sun, Jun 18, 2023 at 11:11:08AM -0700, Ira Weiny wrote:
> Sumitra Sharma wrote:
> > kmap() has been deprecated in favor of the kmap_local_page()
> > due to high cost, restricted mapping space, the overhead of a
> > global lock for synchronization, and making the process sleep
> > in the absence of free slots.
> > 
> > kmap_local_page() is faster than kmap() and offers thread-local
> > and CPU-local mappings, take pagefaults in a local kmap region
> > and preserves preemption by saving the mappings of outgoing tasks
> > and restoring those of the incoming one during a context switch.
> > 
> > The mapping is kept thread local in the function
> > “i915_vma_coredump_create” in i915_gpu_error.c
> > 
> > Therefore, replace kmap() with kmap_local_page().
> > 
> > Suggested-by: Ira Weiny <ira.weiny@...el.com>
> > 
> 
> NIT: No need for the line break between Suggested-by and your signed off line.
> 

Hi Ira,

What does NIT stand for? 

Thank you. I will take care about the line breaks.

> > Signed-off-by: Sumitra Sharma <sumitraartsy@...il.com>
> > ---
> > 
> > Changes in v2:
> > 	- Replace kmap() with kmap_local_page().
> 
> Generally it is customary to attribute a change like this to those who
> suggested it in a V1 review.
> 
> For example:
> 
>  	- Tvrtko/Thomas: Use kmap_local_page() instead of page_address()
> 
> Also I don't see Thomas on the new email list.  Since he took the time to
> review V1 he might want to check this version out.  I've added him to the
> 'To:' list.
> 
> Also a link to V1 is nice.  B4 formats it like this:
> 
> - Link to v1: https://lore.kernel.org/all/20230614123556.GA381200@sumitra.com/
> 
> All that said the code looks good to me.  So with the above changes.
> 
> Reviewed-by: Ira Weiny <ira.weiny@...el.com>
> 

I have noted down the points mentioned above. Thank you again.

I am not supposed to create another version of this patch for 
adding the above mentions, as you and Thomas both gave this patch 
a reviewed-by tag. Right?


Thanks & regards
Sumitra

PS: I am new to the open source vocabulary terms.

> > 	- Change commit subject and message.
> > 
> >  drivers/gpu/drm/i915/i915_gpu_error.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/i915_gpu_error.c b/drivers/gpu/drm/i915/i915_gpu_error.c
> > index f020c0086fbc..bc41500eedf5 100644
> > --- a/drivers/gpu/drm/i915/i915_gpu_error.c
> > +++ b/drivers/gpu/drm/i915/i915_gpu_error.c
> > @@ -1164,9 +1164,9 @@ i915_vma_coredump_create(const struct intel_gt *gt,
> >  
> >  			drm_clflush_pages(&page, 1);
> >  
> > -			s = kmap(page);
> > +			s = kmap_local_page(page);
> >  			ret = compress_page(compress, s, dst, false);
> > -			kunmap(page);
> > +			kunmap_local(s);
> >  
> >  			drm_clflush_pages(&page, 1);
> >  
> > -- 
> > 2.25.1
> > 
> 
>