[PATCH RFC PKS/PMEM 22/58] fs/f2fs: Utilize new kmap_thread()
dave.hansen at intel.com
Mon Oct 12 12:28:29 EDT 2020
On 10/12/20 9:19 AM, Eric Biggers wrote:
> On Sun, Oct 11, 2020 at 11:56:35PM -0700, Ira Weiny wrote:
>>> And I still don't really understand. After this patchset, there is still code
>>> nearly identical to the above (doing a temporary mapping just for a memcpy) that
>>> would still be using kmap_atomic().
>> I don't understand. You mean there would be other call sites calling:
> Yes, there are tons of places that do this. Try 'git grep -A6 kmap_atomic'
> and look for memcpy().
> Hence why I'm asking what will be the "recommended" way to do this...
> kunmap_thread() or kmap_atomic()?
kmap_atomic() is always preferred over kmap()/kmap_thread().
kmap_atomic() is _much_ more lightweight since its TLB invalidation is
always CPU-local and never broadcast.
So, basically, unless you *must* sleep while the mapping is in place,
kmap_atomic() is preferred.
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