Re: [PATCH] General purpose zeroed page slab

[Brian Gerst <bgerst@didntduck.org>]

Martin K. Petersen wrote:
> A while back Bill Irwin converted the page table code on ppc64 to use
> a zeroed page slab.  I recently did the same on ia64 and got a
> significant performance improvement in terms of fault time (4 usec ->
> 700 nsec).
> 
> This cache needs to be initialized fairly early on and so far we've
> called it from pgtable_cache_init() on both archs.  However, Tony Luck
> thought it might be useful to have a general purpose slab cache with
> zeroed pages.  And other architectures might decide to use it for
> their page tables too.
> 
> Consequently here's a patch that puts this functionality in slab.c.
> 
> Signed-off-by: Martin K. Petersen <mkp@wildopensource.com>
> 

This doesn't work as you expect it does.  The constructor is only called 
when a new slab is created, for each new object on the slab.  It is 
_not_ run again when an object is freed.  So if a page is freed then 
immediately reallocated it will contain garbage.

--
				Brian Gerst