4.12-rc ppc64 4k-page needs costly allocations

[Michael Ellerman]

Hugh Dickins <hughd at google.com> writes:

> On Thu, 1 Jun 2017, Christoph Lameter wrote:
>> 
>> Ok so debugging was off but the slab cache has a ctor callback which
>> mandates that the free pointer cannot use the free object space when
>> the object is not in use. Thus the size of the object must be increased to
>> accomodate the freepointer.
>
> Thanks a lot for working that out.  Makes sense, fully understood now,
> nothing to worry about (though makes one wonder whether it's efficient
> to use ctors on high-alignment caches; or whether an internal "zero-me"
> ctor would be useful).

Or should we just be using kmem_cache_zalloc() when we allocate from
those slabs?

Given all the ctor's do is memset to 0.

cheers