On 10/12/20 9:19 AM, Eric Biggers wrote:

On Sun, Oct 11, 2020 at 11:56:35PM -0700, Ira Weiny wrote:

quoted

quoted

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:

kmap_atomic()
memcpy()
kunmap_atomic()

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.