Manfred Spraul wrote:
> Brian Gerst wrote:
>
>>
>> Perhaps, but it currently is already allocating 128 bytes for smaller
>> caches, because the cache is created with SLAB_HWCACHE_ALIGN. So we
>> ended up with redundantly sized caches.
>>
>
> linux/mm/slab.c:
>
>> if (flags & SLAB_HWCACHE_ALIGN) {
>> /* Need to adjust size so that objs are cache aligned. */
>> /* Small obj size, can get at least two per cache line. */
>> while (size < align/2)
>> align /= 2;
>> size = (size+align-1)&(~(align-1));
>> }
>>
>>
> HWALIGN is just a hint, the implementation ignores it if it results in
> unreasonable wasting of memory.
I think I see what was causing be to believe it was always rounding up
to the cache size. The while test should be while (size <= align/2).
On my machine (athlon, 64 byte cache), the size-32 cache was rounded up
to 64 bytes because of this.
size-128 1416 1470 128 49 49 1 : 248 124
size-64 351 413 64 7 7 1 : 248 124
size-32 649 649 64 11 11 1 : 248 124
^^^^
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