mm, slob: rename CONFIG_SLOB to CONFIG_SLOB_DEPRECATED

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@kvack.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.

[1] https://lore.kernel.org/all/b35c3f82-f67b-2103-7d82-7a7ba7521439@suse.cz/

Cc: Russell King <linux@armlinux.org.uk>
Cc: Aaro Koskinen <aaro.koskinen@iki.fi>
Cc: Janusz Krzysztofik <jmkrzyszt@gmail.com>
Cc: Tony Lindgren <tony@atomide.com>
Cc: Jonas Bonn <jonas@southpole.se>
Cc: Stefan Kristiansson <stefan.kristiansson@saunalahti.fi>
Cc: Stafford Horne <shorne@gmail.com>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Cc: Rich Felker <dalias@libc.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Conor Dooley <conor@kernel.org>
Cc: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Aaro Koskinen <aaro.koskinen@iki.fi> # OMAP1
Reviewed-by: Damien Le Moal <damien.lemoal@opensource.wdc.com> # riscv k210
Acked-by: Arnd Bergmann <arnd@arndb.de> # arm
Acked-by: Roman Gushchin <roman.gushchin@linux.dev>
Acked-by: Mike Rapoport <rppt@linux.ibm.com>
Reviewed-by: Christoph Lameter <cl@linux.com>

3 files changed, 6 insertions, 3 deletions

diff --git a/arch/riscv/configs/nommu_k210_defconfig b/arch/riscv/configs/nommu_k210_defconfig
index 96fe8def644c..79b3ccd58ff0 100644
--- a/arch/riscv/configs/nommu_k210_defconfig
+++ b/arch/riscv/configs/nommu_k210_defconfig
@@ -25,7 +25,8 @@ CONFIG_CC_OPTIMIZE_FOR_SIZE=y
 CONFIG_EMBEDDED=y
 # CONFIG_VM_EVENT_COUNTERS is not set
 # CONFIG_COMPAT_BRK is not set
-CONFIG_SLOB=y
+CONFIG_SLUB=y
+CONFIG_SLUB_TINY=y
 # CONFIG_MMU is not set
 CONFIG_SOC_CANAAN=y
 CONFIG_NONPORTABLE=y
diff --git a/arch/riscv/configs/nommu_k210_sdcard_defconfig b/arch/riscv/configs/nommu_k210_sdcard_defconfig
index 379740654373..6b80bb13b8ed 100644
--- a/arch/riscv/configs/nommu_k210_sdcard_defconfig
+++ b/arch/riscv/configs/nommu_k210_sdcard_defconfig
@@ -17,7 +17,8 @@ CONFIG_CC_OPTIMIZE_FOR_SIZE=y
 CONFIG_EMBEDDED=y
 # CONFIG_VM_EVENT_COUNTERS is not set
 # CONFIG_COMPAT_BRK is not set
-CONFIG_SLOB=y
+CONFIG_SLUB=y
+CONFIG_SLUB_TINY=y
 # CONFIG_MMU is not set
 CONFIG_SOC_CANAAN=y
 CONFIG_NONPORTABLE=y
diff --git a/arch/riscv/configs/nommu_virt_defconfig b/arch/riscv/configs/nommu_virt_defconfig
index 1a56eda5ce46..4cf0f297091e 100644
--- a/arch/riscv/configs/nommu_virt_defconfig
+++ b/arch/riscv/configs/nommu_virt_defconfig
@@ -22,7 +22,8 @@ CONFIG_EXPERT=y
 # CONFIG_KALLSYMS is not set
 # CONFIG_VM_EVENT_COUNTERS is not set
 # CONFIG_COMPAT_BRK is not set
-CONFIG_SLOB=y
+CONFIG_SLUB=y
+CONFIG_SLUB_TINY=y
 # CONFIG_MMU is not set
 CONFIG_SOC_VIRT=y
 CONFIG_NONPORTABLE=y