Re: [PATCH] [RFC] xfs: lookaside cache for xfs_buf_find

Mark Tinguely
2013-09-09T15:17:28Z

On 09/08/13 20:33, Dave Chinner wrote:
> From: Dave Chinner<dchinner@redhat.com>
>
> CPU overhead of buffer lookups dominate most metadata intensive
> workloads. The thing is, most such workloads are hitting a
> relatively small number of buffers repeatedly, and so caching
> recently hit buffers is a good idea.
>
> Add a hashed lookaside buffer that records the recent buffer
> lookup successes and is searched first before doing a rb-tree
> lookup. If we get a hit, we avoid the expensive rbtree lookup and
> greatly reduce the overhead of the lookup. If we get a cache miss,
> then we've added an extra CPU cacheline miss into the lookup.

Interesting. The last allocated xfs_buf is placed into the hash.

Might be interesting to know the hit-miss ratio on a real workload.