Re: [PATCH] slab.c cleanup

[Brian Gerst <bgerst@quark.didntduck.org>]

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
                                    ^^^^

--
				Brian Gerst