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Subject[PATCH 0/2] tmpfs: Improve tmpfs scalability

We created a token jar library implementing
per cpu cache of tokens to avoid lock contentions whenever
we retrieve or return a token to a token jar. Using this library
with tmpfs, we find Aim7 fserver throughput improved 270%
on a 4 socket, 32 cores NHM-EX system.

In current implementation of tmpfs, whenever we
get a new page, stat_lock in shmem_sb_info needs to be acquired.
This causes a lot of lock contentions when multiple
threads are using tmpfs simultaneously, which makes
system with large number of cpus scale poorly.
Almost 75% of cpu time was spent contending on
stat_lock when we ran Aim7 fserver load with 128 threads
on a 4 socket, 32 cores NHM-EX system.

The first patch in the series implements the quick token jar.
The second patch update the shmem code of tmpfs to use this
library to improve tmpfs performance.

Tim Chen

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