splice: use get_user_pages_fast
splice: use get_user_pages_fast

Use get_user_pages_fast in splice.  This reverts some mmap_sem batching
there, however the biggest problem with mmap_sem tends to be hold times
blocking out other threads rather than cacheline bouncing.  Further: on
architectures that implement get_user_pages_fast without locks, mmap_sem
can be avoided completely anyway.

Signed-off-by: Nick Piggin <24829078df5003d9dd1dd871ca2aeb0b1cf95ef4@suse.de>
Cc: Dave Kleikamp <9bc4ae2e83dabb4524fc335d7c1dac408a99dbe5@austin.ibm.com>
Cc: Andy Whitcroft <b4658fdd7fbd645c2859b0e39d71018f32058d12@shadowen.org>
Cc: Ingo Molnar <9dbbbf0688fedc85ad4da37637f1a64b8c718ee2@elte.hu>
Cc: Thomas Gleixner <00e4cf8f46a57000a44449bf9dd8cbbcc209fd2a@linutronix.de>
Cc: Andi Kleen <dbd122ef7b6a09ffecf5db9c9296320f3c94e707@firstfloor.org>
Cc: Dave Kleikamp <9bc4ae2e83dabb4524fc335d7c1dac408a99dbe5@austin.ibm.com>
Cc: Badari Pulavarty <a0471031ec5071754e15184cabeebf7217ef1fd9@us.ibm.com>
Cc: Zach Brown <bdd5f2a410e3c75a25da3e38f76d719a18e93cd3@oracle.com>
Cc: Jens Axboe <165ab144a3ccfd9429d5c6466b275f24fafdb114@oracle.com>
Reviewed-by: Peter Zijlstra <645ca7d3a8d3d4f60557176cd361ea8351edc32b@chello.nl>
Signed-off-by: Andrew Morton <5c1e68b099950c134891f0b6e179498a8ebe9cf9@linux-foundation.org>
Signed-off-by: Linus Torvalds <69652caca27c8b940640ad396ab71f93cacec34f@linux-foundation.org>

KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs