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

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Date:   Mon, 3 Jul 2023 11:38:59 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Julian Pidancet <julian.pidancet@...cle.com>
Cc:     David Rientjes <rientjes@...gle.com>,
        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>,
        Rafael Aquini <aquini@...hat.com>
Subject: Re: [PATCH v2] mm/slub: disable slab merging in the default
 configuration

On Mon, Jul 03, 2023 at 12:33:25PM +0200, Julian Pidancet wrote:
> 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.

I think it is a sufficiently complicated heap allocation workload (and
real-world). I'd prefer we get this change landed in -next after -rc1 so
we can see if there are any regressions reported by the 0day and other
CI performance tests.

-Kees

-- 
Kees Cook