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Date:   Mon, 12 Oct 2020 15:40:27 +0800
From:   Coly Li <>
To:     Ira Weiny <>
Cc:     Andrew Morton <>,
        Thomas Gleixner <>,
        Ingo Molnar <>, Borislav Petkov <>,
        Andy Lutomirski <>,
        Peter Zijlstra <>,
        Kent Overstreet <>,,
        Dave Hansen <>,
        Dan Williams <>,
        Fenghua Yu <>,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,
Subject: Re: [PATCH RFC PKS/PMEM 48/58] drivers/md: Utilize new kmap_thread()

On 2020/10/12 13:28, Ira Weiny wrote:
> On Sat, Oct 10, 2020 at 10:20:34AM +0800, Coly Li wrote:
>> On 2020/10/10 03:50, wrote:
>>> From: Ira Weiny <>
>>> These kmap() calls are localized to a single thread.  To avoid the over
>>> head of global PKRS updates use the new kmap_thread() call.
>> Hi Ira,
>> There were a number of options considered.
>> 1) Attempt to change all the thread local kmap() calls to kmap_atomic()
>> 2) Introduce a flags parameter to kmap() to indicate if the mapping
>> should be global or not
>> 3) Change ~20-30 call sites to 'kmap_global()' to indicate that they
>> require a global mapping of the pages
>> 4) Change ~209 call sites to 'kmap_thread()' to indicate that the
>> mapping is to be used within that thread of execution only
>> I copied the above information from patch 00/58 to this message. The
>> idea behind kmap_thread() is fine to me, but as you said the new api is
>> very easy to be missed in new code (even for me). I would like to be
>> supportive to option 2) introduce a flag to kmap(), then we won't forget
>> the new thread-localized kmap method, and people won't ask why a
>> _thread() function is called but no kthread created.
> Thanks for the feedback.
> I'm going to hold off making any changes until others weigh in.  FWIW, I kind
> of like option 2 as well.  But there is already kmap_atomic() so it seemed like
> kmap_XXXX() was more in line with the current API.

I understand it now, the idea is fine to me.

Acked-by: Coly Li <>


Coly Li

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