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Date:   Mon, 9 May 2022 13:43:26 +0200
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Subject: Re: [Patch v3] mm/slub: Remove repeated action in calculate_order()
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To:     Wonhyuk Yang <vvghjk1234@gmail.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>,
        Roman Gushchin <roman.gushchin@linux.dev>,
        Hyeonggon Yoo <42.hyeyoo@gmail.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
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From:   Vlastimil Babka <vbabka@suse.cz>
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On 5/9/22 11:42, Wonhyuk Yang wrote:

>> > +     if (unlikely(order_objects(slub_min_order, size) > MAX_OBJS_PER_PAGE)) {
>> > +             order = get_order(size * MAX_OBJS_PER_PAGE) - 1;
>> > +             goto out;
>> > +     }
>>
>> Hm interestingly, both before and after your patch, MAX_OBJS_PER_PAGE might
>> be theoretically overflowed not by slub_min_order, but then with higher
>> orders. Seems to be prevented only as a side-effect of fragmentation close
>> to none, thus higher orders not attempted. Would be maybe less confusing to
>> check that explicitly. Even if that's wasteful, but this is not really perf
>> critical code.
> 
> Yes, I agree that checking the overflow of object number explicitly is
> better even if
> it is almost impossible. But it checked repeatedly by calling
> calc_slab_order(). It
> seems to me that is unnecessary doesn't it?

Yeah I'm OK with the goal of your patch.