Ben Rockwood wrote:
> I've been pouring through the vdev_cache code and need help
> understanding the cache contents. Per CR 6437054 the cache was said to
> only cache meta-data. However, looking at the current code this no
> longer appears to be the case.
>
> Can someone explain what happened here? The idea of only caching
> metadata is odd to me because when you read-ahead you can't be certain
> of what it is you have put in the cache until someone comes knocking for
> that block.
>
> As I understand the current implementation, the per-disk vdev_caches are
> 10MB LRU. Reads smaller than 16K (cache_max) are inflated to 64K
> (cache_bshift), anything larger than 16K is therefore un-inflated. The
> cache does not differentiate between meta-data blocks and data blocks
> when caching. Is this correct?
>
> Thanks.
>
> benr.
>
Ben,
The code you're looking for is in zio_read_bp_init():
if (!dmu_ot[BP_GET_TYPE(bp)].ot_metadata && BP_GET_LEVEL(bp) == 0)
zio->io_flags |= ZIO_FLAG_DONT_CACHE;
So any data blocks have the ZIO_FLAG_DONT_CACHE flag enabled and won't
end up in the vdev_cache.
Thanks,
George
