linux-kernel - Re: Deprecating and removing SLOB

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Message-ID: <20221109155008.GC307514@darkstar.musicnaut.iki.fi>
Date:   Wed, 9 Nov 2022 17:50:08 +0200
From:   Aaro Koskinen <aaro.koskinen@....fi>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     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

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.

There are OMAP1 boards with only 16 MB, but support for those boards
will be removed. So from OMAP1 side, I don't think there is any real
need for SLOB anymore.

A.