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Date:   Thu, 12 Sep 2019 12:40:35 +0300
From:   "Kirill A. Shutemov" <kirill@shutemov.name>
To:     Yu Zhao <yuzhao@google.com>
Cc:     Christoph Lameter <cl@linux.com>,
        Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 1/4] mm: correct mask size for slub page->objects
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 <20190912023111.219636-1-yuzhao@google.com>
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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@google.com>

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