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

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Date:   Mon, 19 Jun 2023 09:44:20 +0100
From:   Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>
To:     Thomas Hellström (Intel) 
        <thomas_os@...pmail.org>, Ira Weiny <ira.weiny@...el.com>,
        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>,
        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
Cc:     Fabio <fmdefrancesco@...il.com>, Deepak R Varma <drv@...lo.com>
Subject: Re: [PATCH v2] drm/i915: Replace kmap() with kmap_local_page()


On 19/06/2023 08:59, Thomas Hellström (Intel) wrote:
> 
> On 6/18/23 20:11, 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.
>>
>>> 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.
> 
> Thanks.
> 
> 
>> 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>
> 
> LGTM. Reviewed-by: Thomas Hellström <thomas.hellstrom@...ux.intel.com>

Thanks all! I'll just re-send the patch for our CI, since it didn't get 
picked up automatically (stuck in moderation perhaps), with all r-b tags 
added and extra line space removed and merge it if results will be green.

Regards,

Tvrtko