Re: [PATCH RFC PKS/PMEM 48/58] drivers/md: Utilize new kmap_thread()

On Sat, Oct 10, 2020 at 10:20:34AM +0800, Coly Li wrote:

On 2020/10/10 03:50, ira.weiny@intel.com wrote:

quoted

From: Ira Weiny <redacted>

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.

Thanks,
Ira

Thanks.


Coly Li