Re: [RFC, PATCH] set SLAB_HWCACHE_ALIGN for kmalloc caches

[Manfred Spraul <manfred@colorfullife.com>]

Andrew Morton wrote:

>Manfred Spraul <manfred@colorfullife.com> wrote:
>  
>
>>I think the kmalloc caches should remain cache line aligned
>>    
>>
>
>I'm not so sure.  size-64 is used a lot for out-of-line dentry names.
>Taking these up to 128 bytes or even more will consume considerable
>memory in some situations.
>  
>
No, it won't:

>         /* Default alignment: as specified by the arch code.
>          * Except if an object is really small, then squeeze multiple
>          * into one cacheline.
>          */
>         align = cache_line_size();
>         while (size <= align/2)
>                     align /= 2;

SLAB_HWCACHE_ALIGN is still just a hint, for small objects it's 
converted to alignment to a power of two boundary.

--
    Manfred