Re: [patch] Make slab allocator work with SLAB_MUST_HWCACHE_ALIGN

[Arnd Bergmann]

Manfred Spraul wrote:

> But back to the patch that started this thread: Do you still need the 
> ability to set an explicit alignment for slab allocations? If yes, then 
> I'd polish my patch, double check all kmem_cache_create callers and then 
> send the patch to akpm. Otherwise I'd wait - the patch is not a bugfix.

The explicit alignment would be my preferred way to fix slab debugging
on s390. We still have the problem that practically all s390 device drivers
need 64-bit alignment on slab allocations.

Our current hack is to redefine BYTES_PER_WORD in slab.c to 8, but what
I'd like to see is a per-architecture alignment in kmem_cache_init
that would default to 8 on s390 and to sizeof(long) otherwise.

Using the current SLAB_MUST_HWCACHE_ALIGN is not an option since
it wastes a lot of memory with our 2048-bit L1 cache lines.
I'd also like to avoid creating special slab caches for anything
that needs 8-byte alignment.

        Arnd <><
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