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

Ira Weiny
2023-06-18T18:11:29Z

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.

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>

> - 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
>