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

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Message-ID: <648f48bc3d3c2_1de3f9294a3@iweiny-mobl.notmuch>
Date:   Sun, 18 Jun 2023 11:11:08 -0700
From:   Ira Weiny <ira.weiny@...el.com>
To:     Sumitra Sharma <sumitraartsy@...il.com>,
        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>
CC:     Ira Weiny <ira.weiny@...el.com>, 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()

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.

> 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>

> 	- 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
>