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

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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@xxxxxxxxx>

NIT: No need for the line break between Suggested-by and your signed off line.

Signed-off-by: Sumitra Sharma <sumitraartsy@xxxxxxxxx>
---

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@xxxxxxxxxxx/

All that said the code looks good to me.  So with the above changes.

Reviewed-by: Ira Weiny <ira.weiny@xxxxxxxxx>

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




	- 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




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