Re: [PATCH v2 1/4] mm: correct mask size for slub page->objects

[Kirill A. Shutemov]

On Wed, Sep 11, 2019 at 08:31:08PM -0600, Yu Zhao wrote:
> Mask of slub objects per page shouldn't be larger than what
> page->objects can hold.
> 
> It requires more than 2^15 objects to hit the problem, and I don't
> think anybody would. It'd be nice to have the mask fixed, but not
> really worth cc'ing the stable.
> 
> Fixes: 50d5c41cd151 ("slub: Do not use frozen page flag but a bit in the page counters")
> Signed-off-by: Yu Zhao <yuzhao@xxxxxxxxxx>

I don't think the patch fixes anything.

Yes, we have one spare bit between order and number of object that is not
used and always zero. So what?

I can imagine for some microarchitecures accessing higher 16 bits of int
is cheaper than shifting by 15.

-- 
 Kirill A. Shutemov