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

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Message-ID: <f2cc785b-f34a-2a71-78b1-18b4f37de24b@shipmail.org>
Date:   Mon, 19 Jun 2023 09:59:50 +0200
From:   Thomas Hellström (Intel) 
        <thomas_os@...pmail.org>
To:     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>,
        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
Cc:     Fabio <fmdefrancesco@...il.com>, Deepak R Varma <drv@...lo.com>
Subject: Re: [PATCH v2] drm/i915: Replace kmap() with kmap_local_page()


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>



>
>> 	- 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
>>