mm/zswap: change zswap_pool kref to percpu_ref

All zswap entries will take a reference of zswap_pool when zswap_store(),
and drop it when free.  Change it to use the percpu_ref is better for
scalability performance.

Although percpu_ref use a bit more memory which should be ok for our use
case, since we almost have only one zswap_pool to be using.  The
performance gain is for zswap_store/load hotpath.

Testing kernel build (32 threads) in tmpfs with memory.max=2GB.  (zswap
shrinker and writeback enabled with one 50GB swapfile, on a 128 CPUs
x86-64 machine, below is the average of 5 runs)

        mm-unstable  zswap-global-lru
real    63.20        63.12
user    1061.75      1062.95
sys     268.74       264.44

[[email protected]: fix zswap_pools_lock usages after changing to percpu_ref]
  Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Chengming Zhou <[email protected]>
Reviewed-by: Nhat Pham <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Yosry Ahmed <[email protected]>
Cc: Chengming Zhou <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

0 files changed, 0 insertions, 0 deletions