linux-kernel - Re: [PATCH v2] mm/slub: disable slab merging in the default configuration

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Message-Id: <CTSGWINSM18Q.3HQ1DN27GNA1R@imme>
Date:   Mon, 03 Jul 2023 12:33:25 +0200
From:   "Julian Pidancet" <julian.pidancet@...cle.com>
To:     "David Rientjes" <rientjes@...gle.com>
Cc:     "Christoph Lameter" <cl@...ux.com>,
        "Lameter, Christopher" <cl@...amperecomputing.com>,
        "Pekka Enberg" <penberg@...nel.org>,
        "Joonsoo Kim" <iamjoonsoo.kim@....com>,
        "Andrew Morton" <akpm@...ux-foundation.org>,
        "Vlastimil Babka" <vbabka@...e.cz>,
        "Roman Gushchin" <roman.gushchin@...ux.dev>,
        "Hyeonggon Yoo" <42.hyeyoo@...il.com>, <linux-mm@...ck.org>,
        "Jonathan Corbet" <corbet@....net>, <linux-doc@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        "Matthew Wilcox" <willy@...radead.org>,
        "Kees Cook" <keescook@...omium.org>,
        "Rafael Aquini" <aquini@...hat.com>
Subject: Re: [PATCH v2] mm/slub: disable slab merging in the default
 configuration

On Mon Jul 3, 2023 at 02:09, David Rientjes wrote:
> I think we need more data beyond just kernbench.  Christoph's point about 
> different page sizes is interesting.  In the above results, I don't know 
> the page orders for the various slab caches that this workload will 
> stress.  I think the memory overhead data may be different depending on 
> how slab_max_order is being used, if at all.
>
> We should be able to run this through a variety of different benchmarks 
> and measure peak slab usage at the same time for due diligence.  I support 
> the change in the default, I would just prefer to know what the 
> implications of it is.
>
> Is it possible to collect data for other microbenchmarks and real-world 
> workloads?  And perhaps also with different page sizes where this will 
> impact memory overhead more?  I can help running more workloads once we 
> have the next set of data.
>

David,

I agree about the need to perform those tests on hardware using larger
pages. I will collect data if I have the chance to get my hands on one
of these systems.

Do you have specific tests or workload in mind ? Compiling the kernel
with files sitting on an XFS partition is not exhaustive but it is the
only test I could think of that is both easy to set up and can be 
reproduced while keeping external interferences as little as possible.

-- 
Julian

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