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

[Andi Kleen <ak@linux.intel.com>]

, tim wrote:
>
> 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.

I reviewed both patches and they look good to me.
Especially the token jar library should be useful in other places
too.

Reviewed-by: Andi Kleen <ak@linux.intel.com>

-Andi