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