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

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Date:	Fri, 16 Feb 2007 15:33:09 -0800
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Christoph Lameter <clameter@....com>
CC:	Andi Kleen <ak@....de>, Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, virtualization@...ts.osdl.org,
	xen-devel@...ts.xensource.com, Chris Wright <chrisw@...s-sol.org>,
	Zachary Amsden <zach@...are.com>
Subject: Re: [patch 07/21] Xen-paravirt: remove ctor for pgd cache

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
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