tech-kern archive

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Old Index]

Re: Weird PUFFS reclaim activity on netbsd-6

On Thu, Mar 08, 2012 at 05:32:47AM +0100, Emmanuel Dreyfus wrote:
> A posible explanation: perfuse tries to reuse nodes. If the same node is
> looked up twice and not reclaimed in between, perfuse return the same
> node

Further experiments suggest this is the problem. netbsd-6 can lookup 
multiple time the same node without sending a reclaim. But at the end, 
there will be as many reclaims as lookups. If perfuse tracks the 
lookup/reclaim counts and ignore reclaims until it gets to zero, things
seems to work fine.

But this new behavior does not seems very smart on the performance front. 
The kernel sends a lookup for a nodes it already knows, and it sends 
reclaims that must be ignored. In the context of PUFFS filesystem, 
unnecessary VFS ops has a real cost. Is there some rationale behind 
this change?

Emmanuel Dreyfus

Home | Main Index | Thread Index | Old Index