Re: Deprecating and removing SLOB

From: Mike Rapoport <rppt@kernel.org>
To: Aaro Koskinen <aaro.koskinen@iki.fi>
Cc: Vlastimil Babka <vbabka@suse.cz>,
	Pasha Tatashin <pasha.tatashin@soleen.com>,
	Christoph Lameter <cl@linux.com>,
	David Rientjes <rientjes@google.com>,
	Joonsoo Kim <iamjoonsoo.kim@lge.com>,
	Pekka Enberg <penberg@kernel.org>,
	Hyeonggon Yoo <42.hyeyoo@gmail.com>,
	Matthew Wilcox <willy@infradead.org>,
	Roman Gushchin <roman.gushchin@linux.dev>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Rustam Kovhaev <rkovhaev@gmail.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Josh Triplett <josh@joshtriplett.org>,
	Arnd Bergmann <arnd@arndb.de>,
	Russell King <linux@armlinux.org.uk>,
	Alexander Shiyan <shc_work@mail.ru>,
	Janusz Krzysztofik <jmkrzyszt@gmail.com>,
	Tony Lindgren <tony@atomide.com>,
	Yoshinori Sato <ysato@users.sourceforge.jp>,
	Rich Felker <dalias@libc.org>, Jonas Bonn <jonas@southpole.se>,
	Stefan Kristiansson <stefan.kristiansson@saunalahti.fi>,
	Stafford Horne <shorne@gmail.com>,
	"linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>,
	openrisc@lists.librecores.org, linux-riscv@lists.infradead.org,
	linux-sh@vger.kernel.org
Subject: Re: Deprecating and removing SLOB
Date: Wed, 9 Nov 2022 19:45:19 +0200	[thread overview]
Message-ID: <Y2vnLyprF79EQHNz@kernel.org> (raw)
In-Reply-To: <20221109155008.GC307514@darkstar.musicnaut.iki.fi>

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@suse.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.