linux-kernel - Re: [PATCH 12/12] mm, slob: rename CONFIG_SLOB to CONFIG_SLOB

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Message-ID: <53c6d988-7147-2233-6904-f881e7c067b6@suse.cz>
Date:   Mon, 21 Nov 2022 20:42:53 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Christoph Lameter <cl@...ux.com>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Pekka Enberg <penberg@...nel.org>
Cc:     Hyeonggon Yoo <42.hyeyoo@...il.com>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>, patches@...ts.linux.dev,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Russell King <linux@...linux.org.uk>,
        Aaro Koskinen <aaro.koskinen@....fi>,
        Janusz Krzysztofik <jmkrzyszt@...il.com>,
        Tony Lindgren <tony@...mide.com>,
        Jonas Bonn <jonas@...thpole.se>,
        Stefan Kristiansson <stefan.kristiansson@...nalahti.fi>,
        Stafford Horne <shorne@...il.com>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>, Arnd Bergmann <arnd@...db.de>,
        Josh Triplett <josh@...htriplett.org>,
        Conor Dooley <conor@...nel.org>,
        Damien Le Moal <damien.lemoal@...nsource.wdc.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        linux-arm-kernel@...ts.infradead.org, linux-omap@...r.kernel.org,
        openrisc@...ts.librecores.org, linux-riscv@...ts.infradead.org,
        linux-sh@...r.kernel.org
Subject: Re: [PATCH 12/12] mm, slob: rename CONFIG_SLOB to
 CONFIG_SLOB_DEPRECATED

On 11/21/22 18:12, Vlastimil Babka wrote:
> As explained in [1], we would like to remove SLOB if possible.
> 
> - There are no known users that need its somewhat lower memory footprint
>    so much that they cannot handle SLUB (after some modifications by the
>    previous patches) instead.
> 
> - It is an extra maintenance burden, and a number of features are
>    incompatible with it.
> 
> - It blocks the API improvement of allowing kfree() on objects allocated
>    via kmem_cache_alloc().
> 
> As the first step, rename the CONFIG_SLOB option in the slab allocator
> configuration choice to CONFIG_SLOB_DEPRECATED. Add CONFIG_SLOB
> depending on CONFIG_SLOB_DEPRECATED as an internal option to avoid code
> churn. This will cause existing .config files and defconfigs with
> CONFIG_SLOB=y to silently switch to the default (and recommended
> replacement) SLUB, while still allowing SLOB to be configured by anyone
> that notices and needs it. But those should contact the slab maintainers
> and linux-mm@...ck.org as explained in the updated help. With no valid
> objections, the plan is to update the existing defconfigs to SLUB and
> remove SLOB in a few cycles.
> 
> To make SLUB more suitable replacement for SLOB, a CONFIG_SLUB_TINY
> option was introduced to limit SLUB's memory overhead.
> There is a number of defconfigs specifying CONFIG_SLOB=y. As part of
> this patch, update them to select CONFIG_SLUB and CONFIG_SLUB_TINY.

Hm I forgot - some of those defconfigs might not actually be for so tiny 
devices to need CONFIG_SLUB_TINY (or SLOB previously). For those it 
would make more sense to simply remove CONFIG_SLOB=y and leave it to the 
default choice, which is SLUB (without _TINY). Feel free to point those 
out to me and I'll adjust. Thanks.

> [1] https://lore.kernel.org/all/b35c3f82-f67b-2103-7d82-7a7ba7521439@suse.cz/
> 
> Cc: Russell King <linux@...linux.org.uk>
> Cc: Aaro Koskinen <aaro.koskinen@....fi>
> Cc: Janusz Krzysztofik <jmkrzyszt@...il.com>
> Cc: Tony Lindgren <tony@...mide.com>
> Cc: Jonas Bonn <jonas@...thpole.se>
> Cc: Stefan Kristiansson <stefan.kristiansson@...nalahti.fi>
> Cc: Stafford Horne <shorne@...il.com>
> Cc: Yoshinori Sato <ysato@...rs.sourceforge.jp>
> Cc: Rich Felker <dalias@...c.org>
> Cc: Arnd Bergmann <arnd@...db.de>
> Cc: Josh Triplett <josh@...htriplett.org>
> Cc: Conor Dooley <conor@...nel.org>
> Cc: Damien Le Moal <damien.lemoal@...nsource.wdc.com>
> Cc: Christophe Leroy <christophe.leroy@...roup.eu>
> Cc: Geert Uytterhoeven <geert@...ux-m68k.org>
> Cc: <linux-arm-kernel@...ts.infradead.org>
> Cc: <linux-omap@...r.kernel.org>
> Cc: <openrisc@...ts.librecores.org>
> Cc: <linux-riscv@...ts.infradead.org>
> Cc: <linux-sh@...r.kernel.org>
> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>