Re: [PATCH] Move slab objects to the end of the real allocation

[Manfred Spraul]

Arnd Bergmann wrote:

> Manfred Spraul wrote:
>  
>
> >   - Do not page-pad allocations that are <= SMP_CACHE_LINE_SIZE.  This
> >     crashes.  Right now the limit is hardcoded to 128 bytes, but sooner or
> >     later an arch will appear with 256 byte cache lines.
> >    
>
> What made you think that 128 is the current maximum? All s390 machines
> have 256 byte cache lines.
>  
When I wrote "128" I was not aware that this is linked to the cache line 
size. Initially it was ">128", just as an arbitrary number. I replaced 
that with "> 116" due to an unrelated change, and that crashed, because 
the cache line size was set to 128 bytes.

My patch fixes this bug: It replaces the limits with >=116 [avoid 
wasting too much memory, guarantee that there is a cache for the 
off-slab control structures] and > SMP_CACHE_LINE_SIZE [guarantee that 
there is a cache for the off-slab control structures].

Right now there are too many patches in Andrew's tree, I'll wait until 
everything settled down a bit, then I'll resent the cache line size as a 
one-line patch. Do you want to implement CONFIG_DEBUG_PAGEALLOC 
immediately? If yes, then I can send you the oneliner immediately. 
Nothing except CONFIG_DEBUG_PAGEALLOC is affected by the bug.

--
   Manfred

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