Re: [patch 07/21] Xen-paravirt: remove ctor for pgd cache

Jeremy Fitzhardinge
2007-02-16T23:33:11Z

Christoph Lameter wrote:
> On Thu, 15 Feb 2007, Jeremy Fitzhardinge wrote:
>
>
>> Remove the ctor for the pgd cache. There's no point in having the
>> cache machinery do this via an indirect call when all pgd are freed in
>> the one place anyway.
>>
>
> Great. We finally get rid of this evil .....
>
> On second throughts:
>
> Are you sure that you understand what you are modifying? The ctor is not
> called when you allocate an object but when the slab allocates it. Freeing
> an object does not make the slab free it. It will hold it for the next
> kmalloc. So you may just have reduced performance somewhat by addiung
> additional ctor processing and possibly disturbed the preservation of
> cache hot pgds.
It's true I wrote this patch as a result of accidentally reading slob.c
rather than slab.c, which was mostly as a result of hopeful thinking (I
knew that there has been discussion about removing all the slab cache
stuff, and I assumed that it had already happened). As a result I'm
withdrawing this patch for now, but with any luck it will be useful at
some point.

J