Re: kernel memory allocators

[Andrew Doran <ad%netbsd.org@localhost>]

On Thu, Jan 20, 2011 at 02:11:59AM +0000, YAMAMOTO Takashi wrote:
> hi,
> 
> > Benefits I've thought about:
> > - The kmem pools use pool_caches therefor scalability will be much
> > better as the old malloc has a single lock for all access, the pools
> > have one each with a per cpu cache layer.
> > - The old malloc only returns oversized allocations back to the kmem
> > layer but nothing that is in it's bucket, pools can be drained...
> > - Removing one redundant interface in the kernel-api (in the long
> > term, when dropping the malloc wrapper)
> 
> thanks for working on this.
> while i'm all for removing malloc(9), i tend to think it should be done
> by changing the users to use either kmem_alloc or pool_cache, instead of
> making kmem_alloc interrupt-safe.  i don't think there's much demand for
> interrupt-safe variable-sized memory allocations.

Agreed.  Variable-sized allocations from interrupt context are indicative
of a design flaw.  Either the processing should happen at another level,
or allocations should be from a pool (whether that is pool_cache or some
private mechanism).