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Date:   Mon, 24 Feb 2020 01:29:09 +0000 (UTC)
From:   Christopher Lameter <cl@linux.com>
To:     Wen Yang <wenyang@linux.alibaba.com>
cc:     Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Roman Gushchin <guro@fb.com>,
        Xunlei Pang <xlpang@linux.alibaba.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm/slub: improve count_partial() for
 CONFIG_SLUB_CPU_PARTIAL
In-Reply-To: <20200222092428.99488-1-wenyang@linux.alibaba.com>
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References: <20200222092428.99488-1-wenyang@linux.alibaba.com>
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On Sat, 22 Feb 2020, Wen Yang wrote:

> We also observed that in this scenario, CONFIG_SLUB_CPU_PARTIAL is turned
> on by default, and count_partial() is useless because the returned number
> is far from the reality.

Well its not useless. Its just not counting the partial objects in per cpu
partial slabs. Those are counted by a different counter it.

> Therefore, we can simply return 0, then nr_free is also 0, and eventually
> active_objects == total_objects. We do not introduce any regression, and
> it's preferable to show the unrealistic uniform 100% slab utilization
> rather than some very high but incorrect value.

I suggest that you simply use the number of partial slabs and multiply
them by the number of objects in a slab and use that as a value. Both
values are readily available via /sys/kernel/slab/<...>/

You dont need a patch to do that.