On Sun, Jul 23, 2006 at 06:03:09AM -0700, Christoph Lameter wrote:
> 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.
CONFIG_DEBUG_SLAB is on. In step 4) we have align = ralign.
Still ok.
Next thing:
if (flags & SLAB_RED_ZONE) {
/* redzoning only works with word aligned caches */
align = BYTES_PER_WORD;
Result: align is less than ARCH_SLAB_MINALIGN -> busted.
Same is true if SLAB_STORE_USER is set.
Therefore I masked them both out in my patch.
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