Re: [GIT PULL] SLAB changes for v3.10

[Christoph Lameter]

On Wed, 8 May 2013, Chris Mason wrote:

> > You correctly moved the checks out of the if (!kmalloc_cacheS())
> > condition so that the caches are created properly.
>
> But if the ordering is required at all, why is it ok to create cache 2
> after cache 6 instead of after cache 7?

The power of two caches are 2^x beginning with KMALLOC_MIN_SHIFT. The non
power of two caches were folded into number 1 + 2 since they do not fit
into the scheme and they are special cased throughout. This works since
the minimal slab cache size is 8 bytes.

> IOW if we can safely do cache 2 after cache 6, why can't we just do both
> cache 1 and cache 2 after the loop?

Because the cache creation in SLAB can cause the use of a fractional slab
size if kmem_cache_create() thinks its better to put the metadata on a
different slab cache (OFF_SLAB type) because data will align better that
way. Its weird I know but its due to the way that SLAB aligns data in the
page frame.

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