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

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Message-ID: <d7a6f81e-94b8-1cb3-5fd6-ac944a052470@linux.intel.com>
Date:   Mon, 26 Jun 2023 10:02:18 +0100
From:   Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>
To:     Ira Weiny <ira.weiny@...el.com>,
        Sumitra Sharma <sumitraartsy@...il.com>
Cc:     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,
        Thomas Hellström (Intel) 
        <thomas_os@...pmail.org>, Fabio <fmdefrancesco@...il.com>,
        Deepak R Varma <drv@...lo.com>
Subject: Re: [PATCH v2] drm/i915: Replace kmap() with kmap_local_page()


On 20/06/2023 14:23, Ira Weiny wrote:
> Sumitra Sharma wrote:
>> On Sun, Jun 18, 2023 at 11:11:08AM -0700, 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.
>>>
>>
>> Hi Ira,
>>
>> What does NIT stand for?
> 
> Shorthand for 'nitpicking'.
> 
> "giving too much attention to details that are not important, especially
> as a way of criticizing: "
> 
> 	- https://dictionary.cambridge.org/dictionary/english/nitpicking
> 
> Via email this is a way for authors of an email to indicate something is
> technically wrong but while nicely acknowledging that it is not very
> significant and could be seen as overly critical.
> 
> For this particular comment I'm showing something to pay attention to next
> time but that was not a big deal this time around.
> 
>>
>> Thank you. I will take care about the line breaks.
>>
>>>> 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.
>>>
>>> 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>
>>>
>>
>> I have noted down the points mentioned above. Thank you again.
>>
>> I am not supposed to create another version of this patch for
>> adding the above mentions, as you and Thomas both gave this patch
>> a reviewed-by tag. Right?
>>
> 
> Based on this response[*] from Tvrtko I think this version can move
> through without a v3.
> 
> Thanks!
> Ira
> 
> [*] https://lore.kernel.org/all/bcb0a1d2-cd4d-a56f-1ee6-7ccfdd2f7b38@linux.intel.com/
> 
> <quote>
> 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
> </quote>

Pushed to drm-intel-gt-next, thanks for the patch and reviews!

Regards,

Tvrtko