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Date:   Fri, 17 Jun 2022 16:19:47 +0200 (CEST)
From:   Christoph Lameter <cl@gentwo.de>
To:     Rongwei Wang <rongwei.wang@linux.alibaba.com>
cc:     David Rientjes <rientjes@google.com>, songmuchun@bytedance.com,
        Hyeonggon Yoo <42.hyeyoo@gmail.com>, akpm@linux-foundation.org,
        vbabka@suse.cz, roman.gushchin@linux.dev, iamjoonsoo.kim@lge.com,
        penberg@kernel.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/3] mm/slub: fix the race between validate_slab and
 slab_free
In-Reply-To: <5085437c-adc9-b6a3-dbd8-91dc0856cf19@linux.alibaba.com>
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References: <20220529081535.69275-1-rongwei.wang@linux.alibaba.com> <YpNa4tB/jfW3MDyi@n2.us-central1-a.c.spheric-algebra-350919.internal> <ac9ba68f-9ee2-1611-9ff8-b486ed9c4df0@google.com> <alpine.DEB.2.22.394.2206021712530.2924@gentwo.de>
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On Fri, 17 Jun 2022, Rongwei Wang wrote:

> Christoph, I refer [1] to test some data below. The slub_test case is same to
> your provided. And here you the result of its test (the baseline is the data
> of upstream kernel, and fix is results of patched kernel).

Ah good.
> Single thread testing
>
> 1. Kmalloc: Repeatedly allocate then free test
>
>                    before (baseline)        fix
>                    kmalloc      kfree       kmalloc      kfree
> 10000 times 8      7 cycles     8 cycles    5 cycles     7 cycles
> 10000 times 16     4 cycles     8 cycles    3 cycles     6 cycles
> 10000 times 32     4 cycles     8 cycles    3 cycles     6 cycles

Well the cycle reduction is strange. Tests are not done in the same
environment? Maybe good to not use NUMA or bind to the same cpu

> 10000 times 64     3 cycles     8 cycles    3 cycles     6 cycles
> 10000 times 128    3 cycles     8 cycles    3 cycles     6 cycles
> 10000 times 256    12 cycles    8 cycles    11 cycles    7 cycles
> 10000 times 512    27 cycles    10 cycles   23 cycles    11 cycles
> 10000 times 1024   18 cycles    9 cycles    20 cycles    10 cycles
> 10000 times 2048   54 cycles    12 cycles   54 cycles    12 cycles
> 10000 times 4096   105 cycles   20 cycles   105 cycles   25 cycles
> 10000 times 8192   210 cycles   35 cycles   212 cycles   39 cycles
> 10000 times 16384  133 cycles   45 cycles   119 cycles   46 cycles


Seems to be different environments.

> According to the above data, It seems that no significant performance
> degradation in patched kernel. Plus, in concurrent allocs test, likes Kmalloc
> N*alloc N*free(1024), the data of 'fix' column is better than baseline (it
> looks less is better, if I am wrong, please let me know). And if you have
> other suggestions, I can try to test more data.

Well can you explain the cycle reduction?