Re: [PATCH] Btrfs: save preloaded extent_state's in a percpu cache V2

[Josef Bacik <josef@redhat.com>]

On 06/21/2011 04:20 PM, Andi Kleen wrote:
> Josef Bacik <josef@redhat.com> writes:
> 
>> When doing DIO tracing I noticed we were doing a ton of allocations, a lot of
>> the time for extent_states.  Some of the time we don't even use the prealloc'ed
>> extent_state, it just get's free'd up.  So instead create a per-cpu cache like
>> the radix tree stuff.  So we will check to see if our per-cpu cache has a
>> prealloc'ed extent_state in it and if so we just continue, else we alloc a new
>> one and fill the cache.  Then if we need to use a prealloc'ed extent_state we
>> can just take it out of our per-cpu cache.  We will also refill the cache on
>> free to try and limit the number of times we have to ask the allocator for
>> caches.  With this patch dbench 50 goes from ~210 mb/s to ~260 mb/s.  Thanks,
> 
> You're just reimplementing a poor man's custom slab cache -- all of this is already
> done in slab.
> 
> If the difference is really that big better fix slab and have everyone 
> benefit?
> 
> Did you use slub or slab?
> Did you analyze where the cycles are spent?
> 

Ugh slub debugging bites me again.  Thanks,

Josef