Re: [PATCH] slab: introduce kmem_cache_zalloc allocator

[Manfred Spraul]

Pekka J Enberg wrote:

> On Tue, 21 Mar 2006, Andrew Morton wrote:
>  
>
> > I've always felt that this was an odd design.  Because
> >
> > a) All that cache-warmth which we get from the constructor's zeroing can
> >   be lost by the time we get around to using an individual object and
> >
> > b) The object may be cache-cold by the time we free it, and we'll take
> >   cache misses just putting it back into a constructed state for
> >   kmem_cache_free().  And we'll lose that cache warmth by the time we use
> >   this object again.
> >
> > So from that POV I think (in my simple way) that this is a good patch.  But
> > IIRC, Manfred has reasons why it might not be?
> >    
>
> I assume the design comes from Bonwick's paper which states that the 
> purpose of object constructor is to support one-time initialization of 
> objects which we're _not_ doing in this case.
>
>  
I agree - memset just before use is the Right Thing (tm).

One minor point: There are two cache_alloc entry points: __cache_alloc, 
which is a forced inline function, and kmem_cache_alloc, which is just a 
wrapper for __cache_alloc. Is it really necessary to call __cache_alloc?
The idea is that __cache_alloc is used just by the two high-performance 
paths: kmem_cache_alloc and kmalloc. Noone else should use __cache_alloc 
directly.

--
   Manfred
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