linux-kernel - Re: Deprecating and removing SLOB

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Date:   Wed, 9 Nov 2022 19:45:19 +0200
From:   Mike Rapoport <rppt@...nel.org>
To:     Aaro Koskinen <aaro.koskinen@....fi>
Cc:     Vlastimil Babka <vbabka@...e.cz>,
        Pasha Tatashin <pasha.tatashin@...een.com>,
        Christoph Lameter <cl@...ux.com>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Pekka Enberg <penberg@...nel.org>,
        Hyeonggon Yoo <42.hyeyoo@...il.com>,
        Matthew Wilcox <willy@...radead.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Rustam Kovhaev <rkovhaev@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Josh Triplett <josh@...htriplett.org>,
        Arnd Bergmann <arnd@...db.de>,
        Russell King <linux@...linux.org.uk>,
        Alexander Shiyan <shc_work@...l.ru>,
        Janusz Krzysztofik <jmkrzyszt@...il.com>,
        Tony Lindgren <tony@...mide.com>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>, Jonas Bonn <jonas@...thpole.se>,
        Stefan Kristiansson <stefan.kristiansson@...nalahti.fi>,
        Stafford Horne <shorne@...il.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        openrisc@...ts.librecores.org, linux-riscv@...ts.infradead.org,
        linux-sh@...r.kernel.org
Subject: Re: Deprecating and removing SLOB

On Wed, Nov 09, 2022 at 05:50:08PM +0200, Aaro Koskinen wrote:
> Hi,
> 
> On Wed, Nov 09, 2022 at 10:00:25AM +0100, Vlastimil Babka wrote:
> > > On Tue, Nov 8, 2022 at 10:55 AM Vlastimil Babka <vbabka@...e.cz> wrote:
> > >> I believe SLOB can be removed because:
> > >>
> > >> - AFAIK nobody really uses it? It strives for minimal memory footprint
> > >> by putting all objects together, which has its CPU performance costs
> > >> (locking, lack of percpu caching, searching for free space...). I'm not
> > >> aware of any "tiny linux" deployment that opts for this. For example,
> > >> OpenWRT seems to use SLUB and the devices these days have e.g. 128MB
> > >> RAM, not up to 16 MB anymore. I've heard anecdotes that the performance
> > >> SLOB impact is too much for those who tried. Googling for
> > >> "CONFIG_SLOB=y" yielded nothing useful.
> > > 
> > > I am all for removing SLOB.
> > > 
> > > There are some devices with configs where SLOB is enabled by default.
> > > Perhaps, the owners/maintainers of those devices/configs should be
> > > included into this thread:
> 
> [...]
> 
> > > arch/arm/configs/omap1_defconfig:CONFIG_SLOB=y
> 
> I have been using SLUB on my OMAP1 boards with 32 MB RAM, because of
> better debugging features and the memory footprint difference doesn't
> really matter for my use cases. Looking at history why SLOB was added
> there, it seems it came from 6cfce27c14aa ("omap1: Add omap1_defconfig")
> when separate boards configs were merged, and SX1 board happened to have
> SLOB in there. This board is nowadays only used in QEMU anyway.

Looks like the same happened with arch/arm/configs/pxa_defconfig. XCEP
board had SLOB in its defconfig and when common pxa_defconfig was created
it apparently used it.
Looks like the board has 64M of RAM, so dropping CONFIG_SLOB=y from
arch/arm/configs/pxa_defconfig and arch/arm/configs/xcep_defconfig seems
very reasonable.

-- 
Sincerely yours,
Mike.