Re: [Intel-gfx] [PATCH v2] drm/i915: Replace kmap() with kmap_local_page()

Thomas Hellström (Intel)
2023-06-19T07:59:58Z

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@intel.com>
>>
> NIT: No need for the line break between Suggested-by and your signed off line.
>
>> Signed-off-by: Sumitra Sharma <sumitraartsy@gmail.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@intel.com>

LGTM. Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.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
>>