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SubjectRe: [patch] slab: always follow arch requested alignments
On Sun, 23 Jul 2006, Heiko Carstens wrote:

> >
> > See kmem_cache_create():
> > /* 2) arch mandated alignment: disables debug if necessary */
> > if (ralign < ARCH_SLAB_MINALIGN) {
> > ralign = ARCH_SLAB_MINALIGN;
> > if (ralign > BYTES_PER_WORD)
> > flags &= ~(SLAB_RED_ZONE | SLAB_STORE_USER);
> > }
>
> That is because if kmem_cache_create gets called with SLAB_HWCACHE_ALIGN set
> in flags then ralign will be greater or equal to ARCH_SLAB_MINALIGN:
>
> /* 1) arch recommendation: can be overridden for debug */
> if (flags & SLAB_HWCACHE_ALIGN) {
> [...]
> ralign = cache_line_size();
> [...]

Ok. Then you do not have a problem because ralign is greater than
ARCH_SLAB_MINALIGN.

> Therefore the test above will be passed and SLAB_RED_ZONE and SLAB_STORE_USER
> will stay in flags.
> cache_line_size() will return 256 on s390.

Looks as if you would have the correct alignment then. I still do not
understand where the problem is since you want to align on an 8 byte
boundary.


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