Re: [PATCH 12/12] mm, slob: rename CONFIG_SLOB to CONFIG_SLOB_DEPRECATED

From: Vlastimil Babka
Date: Mon Nov 21 2022 - 14:44:48 EST


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@xxxxxxxxx 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@xxxxxxx/

Cc: Russell King <linux@xxxxxxxxxxxxxxx>
Cc: Aaro Koskinen <aaro.koskinen@xxxxxx>
Cc: Janusz Krzysztofik <jmkrzyszt@xxxxxxxxx>
Cc: Tony Lindgren <tony@xxxxxxxxxxx>
Cc: Jonas Bonn <jonas@xxxxxxxxxxxx>
Cc: Stefan Kristiansson <stefan.kristiansson@xxxxxxxxxxxxx>
Cc: Stafford Horne <shorne@xxxxxxxxx>
Cc: Yoshinori Sato <ysato@xxxxxxxxxxxxxxxxxxxx>
Cc: Rich Felker <dalias@xxxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
Cc: Conor Dooley <conor@xxxxxxxxxx>
Cc: Damien Le Moal <damien.lemoal@xxxxxxxxxxxxxxxxxx>
Cc: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
Cc: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
Cc: <linux-arm-kernel@xxxxxxxxxxxxxxxxxxx>
Cc: <linux-omap@xxxxxxxxxxxxxxx>
Cc: <openrisc@xxxxxxxxxxxxxxxxxxxx>
Cc: <linux-riscv@xxxxxxxxxxxxxxxxxxx>
Cc: <linux-sh@xxxxxxxxxxxxxxx>
Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>