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

From: Palmer Dabbelt
Date: Fri Dec 02 2022 - 12:59:28 EST

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On Mon, 21 Nov 2022 09:12:02 PST (-0800), vbabka@xxxxxxx 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.

[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>
---
arch/arm/configs/clps711x_defconfig | 3 ++-
arch/arm/configs/collie_defconfig | 3 ++-
arch/arm/configs/multi_v4t_defconfig | 3 ++-
arch/arm/configs/omap1_defconfig | 3 ++-
arch/arm/configs/pxa_defconfig | 3 ++-
arch/arm/configs/tct_hammer_defconfig | 3 ++-
arch/arm/configs/xcep_defconfig | 3 ++-
arch/openrisc/configs/or1ksim_defconfig | 3 ++-
arch/openrisc/configs/simple_smp_defconfig | 3 ++-
arch/riscv/configs/nommu_k210_defconfig | 3 ++-
arch/riscv/configs/nommu_k210_sdcard_defconfig | 3 ++-
arch/riscv/configs/nommu_virt_defconfig | 3 ++-
arch/sh/configs/rsk7201_defconfig | 3 ++-
arch/sh/configs/rsk7203_defconfig | 3 ++-
arch/sh/configs/se7206_defconfig | 3 ++-
arch/sh/configs/shmin_defconfig | 3 ++-
arch/sh/configs/shx3_defconfig | 3 ++-
kernel/configs/tiny.config | 5 +++--
mm/Kconfig | 17 +++++++++++++++--
19 files changed, 52 insertions(+), 21 deletions(-)

diff --git a/arch/arm/configs/clps711x_defconfig b/arch/arm/configs/clps711x_defconfig
index 92481b2a88fa..adcee238822a 100644
--- a/arch/arm/configs/clps711x_defconfig
+++ b/arch/arm/configs/clps711x_defconfig
@@ -14,7 +14,8 @@ CONFIG_ARCH_EDB7211=y
CONFIG_ARCH_P720T=y
CONFIG_AEABI=y
# CONFIG_COREDUMP is not set
-CONFIG_SLOB=y
+CONFIG_SLUB=y
+CONFIG_SLUB_TINY=y
CONFIG_NET=y
CONFIG_PACKET=y
CONFIG_UNIX=y
diff --git a/arch/arm/configs/collie_defconfig b/arch/arm/configs/collie_defconfig
index 2a2d2cb3ce2e..69341c33e0cc 100644
--- a/arch/arm/configs/collie_defconfig
+++ b/arch/arm/configs/collie_defconfig
@@ -13,7 +13,8 @@ CONFIG_CMDLINE="noinitrd root=/dev/mtdblock2 rootfstype=jffs2 fbcon=rotate:1"
CONFIG_FPE_NWFPE=y
CONFIG_PM=y
# CONFIG_SWAP is not set
-CONFIG_SLOB=y
+CONFIG_SLUB=y
+CONFIG_SLUB_TINY=y
CONFIG_NET=y
CONFIG_PACKET=y
CONFIG_UNIX=y
diff --git a/arch/arm/configs/multi_v4t_defconfig b/arch/arm/configs/multi_v4t_defconfig
index e2fd822f741a..b60000a89aff 100644
--- a/arch/arm/configs/multi_v4t_defconfig
+++ b/arch/arm/configs/multi_v4t_defconfig
@@ -25,7 +25,8 @@ CONFIG_ARM_CLPS711X_CPUIDLE=y
CONFIG_JUMP_LABEL=y
CONFIG_PARTITION_ADVANCED=y
# CONFIG_COREDUMP is not set
-CONFIG_SLOB=y
+CONFIG_SLUB=y
+CONFIG_SLUB_TINY=y
CONFIG_MTD=y
CONFIG_MTD_CMDLINE_PARTS=y
CONFIG_MTD_BLOCK=y
diff --git a/arch/arm/configs/omap1_defconfig b/arch/arm/configs/omap1_defconfig
index 70511fe4b3ec..246f1bba7df5 100644
--- a/arch/arm/configs/omap1_defconfig
+++ b/arch/arm/configs/omap1_defconfig
@@ -42,7 +42,8 @@ CONFIG_MODULE_FORCE_UNLOAD=y
CONFIG_PARTITION_ADVANCED=y
CONFIG_BINFMT_MISC=y
# CONFIG_SWAP is not set
-CONFIG_SLOB=y
+CONFIG_SLUB=y
+CONFIG_SLUB_TINY=y
# CONFIG_VM_EVENT_COUNTERS is not set
CONFIG_NET=y
CONFIG_PACKET=y
diff --git a/arch/arm/configs/pxa_defconfig b/arch/arm/configs/pxa_defconfig
index d60cc9cc4c21..0a0f12df40b5 100644
--- a/arch/arm/configs/pxa_defconfig
+++ b/arch/arm/configs/pxa_defconfig
@@ -49,7 +49,8 @@ CONFIG_PARTITION_ADVANCED=y
CONFIG_LDM_PARTITION=y
CONFIG_CMDLINE_PARTITION=y
CONFIG_BINFMT_MISC=y
-CONFIG_SLOB=y
+CONFIG_SLUB=y
+CONFIG_SLUB_TINY=y
# CONFIG_COMPACTION is not set
CONFIG_NET=y
CONFIG_PACKET=y
diff --git a/arch/arm/configs/tct_hammer_defconfig b/arch/arm/configs/tct_hammer_defconfig
index 3b29ae1fb750..6bd38b6f22c4 100644
--- a/arch/arm/configs/tct_hammer_defconfig
+++ b/arch/arm/configs/tct_hammer_defconfig
@@ -19,7 +19,8 @@ CONFIG_FPE_NWFPE=y
CONFIG_MODULES=y
CONFIG_MODULE_UNLOAD=y
# CONFIG_SWAP is not set
-CONFIG_SLOB=y
+CONFIG_SLUB=y
+CONFIG_SLUB_TINY=y
CONFIG_NET=y
CONFIG_PACKET=y
CONFIG_UNIX=y
diff --git a/arch/arm/configs/xcep_defconfig b/arch/arm/configs/xcep_defconfig
index ea59e4b6bfc5..6bd9f71b71fc 100644
--- a/arch/arm/configs/xcep_defconfig
+++ b/arch/arm/configs/xcep_defconfig
@@ -26,7 +26,8 @@ CONFIG_MODULE_UNLOAD=y
CONFIG_MODVERSIONS=y
CONFIG_MODULE_SRCVERSION_ALL=y
# CONFIG_BLOCK is not set
-CONFIG_SLOB=y
+CONFIG_SLUB=y
+CONFIG_SLUB_TINY=y
# CONFIG_COMPAT_BRK is not set
# CONFIG_VM_EVENT_COUNTERS is not set
CONFIG_NET=y
diff --git a/arch/openrisc/configs/or1ksim_defconfig b/arch/openrisc/configs/or1ksim_defconfig
index 6e1e004047c7..0116e465238f 100644
--- a/arch/openrisc/configs/or1ksim_defconfig
+++ b/arch/openrisc/configs/or1ksim_defconfig
@@ -10,7 +10,8 @@ CONFIG_EXPERT=y
# CONFIG_AIO 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_MODULES=y
# CONFIG_BLOCK is not set
CONFIG_OPENRISC_BUILTIN_DTB="or1ksim"
diff --git a/arch/openrisc/configs/simple_smp_defconfig b/arch/openrisc/configs/simple_smp_defconfig
index ff49d868e040..b990cb6c9309 100644
--- a/arch/openrisc/configs/simple_smp_defconfig
+++ b/arch/openrisc/configs/simple_smp_defconfig
@@ -16,7 +16,8 @@ CONFIG_EXPERT=y
# CONFIG_AIO 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_MODULES=y
# CONFIG_BLOCK is not set
CONFIG_OPENRISC_BUILTIN_DTB="simple_smp"
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

Acked-by: Palmer Dabbelt <palmer@xxxxxxxxxxxx>

Though I don't have a K210 to test against, maybe Damien still does?

diff --git a/arch/sh/configs/rsk7201_defconfig b/arch/sh/configs/rsk7201_defconfig
index 619c18699459..376e95fa77bc 100644
--- a/arch/sh/configs/rsk7201_defconfig
+++ b/arch/sh/configs/rsk7201_defconfig
@@ -10,7 +10,8 @@ CONFIG_USER_NS=y
CONFIG_PID_NS=y
CONFIG_BLK_DEV_INITRD=y
# CONFIG_AIO is not set
-CONFIG_SLOB=y
+CONFIG_SLUB=y
+CONFIG_SLUB_TINY=y
CONFIG_PROFILING=y
CONFIG_MODULES=y
# CONFIG_BLK_DEV_BSG is not set
diff --git a/arch/sh/configs/rsk7203_defconfig b/arch/sh/configs/rsk7203_defconfig
index d00fafc021e1..1d5fd67a3949 100644
--- a/arch/sh/configs/rsk7203_defconfig
+++ b/arch/sh/configs/rsk7203_defconfig
@@ -11,7 +11,8 @@ CONFIG_USER_NS=y
CONFIG_PID_NS=y
CONFIG_BLK_DEV_INITRD=y
CONFIG_KALLSYMS_ALL=y
-CONFIG_SLOB=y
+CONFIG_SLUB=y
+CONFIG_SLUB_TINY=y
CONFIG_PROFILING=y
CONFIG_MODULES=y
# CONFIG_BLK_DEV_BSG is not set
diff --git a/arch/sh/configs/se7206_defconfig b/arch/sh/configs/se7206_defconfig
index 122216123e63..78e0e7be57ee 100644
--- a/arch/sh/configs/se7206_defconfig
+++ b/arch/sh/configs/se7206_defconfig
@@ -21,7 +21,8 @@ CONFIG_BLK_DEV_INITRD=y
CONFIG_KALLSYMS_ALL=y
# CONFIG_ELF_CORE is not set
# CONFIG_COMPAT_BRK is not set
-CONFIG_SLOB=y
+CONFIG_SLUB=y
+CONFIG_SLUB_TINY=y
CONFIG_PROFILING=y
CONFIG_MODULES=y
CONFIG_MODULE_UNLOAD=y
diff --git a/arch/sh/configs/shmin_defconfig b/arch/sh/configs/shmin_defconfig
index c0b6f40d01cc..e078b193a78a 100644
--- a/arch/sh/configs/shmin_defconfig
+++ b/arch/sh/configs/shmin_defconfig
@@ -9,7 +9,8 @@ CONFIG_LOG_BUF_SHIFT=14
# CONFIG_FUTEX is not set
# CONFIG_EPOLL is not set
# CONFIG_SHMEM is not set
-CONFIG_SLOB=y
+CONFIG_SLUB=y
+CONFIG_SLUB_TINY=y
# CONFIG_BLK_DEV_BSG is not set
CONFIG_CPU_SUBTYPE_SH7706=y
CONFIG_MEMORY_START=0x0c000000
diff --git a/arch/sh/configs/shx3_defconfig b/arch/sh/configs/shx3_defconfig
index 32ec6eb1eabc..aa353dff7f19 100644
--- a/arch/sh/configs/shx3_defconfig
+++ b/arch/sh/configs/shx3_defconfig
@@ -20,7 +20,8 @@ CONFIG_USER_NS=y
CONFIG_PID_NS=y
# CONFIG_CC_OPTIMIZE_FOR_SIZE is not set
CONFIG_KALLSYMS_ALL=y
-CONFIG_SLOB=y
+CONFIG_SLUB=y
+CONFIG_SLUB_TINY=y
CONFIG_PROFILING=y
CONFIG_KPROBES=y
CONFIG_MODULES=y
diff --git a/kernel/configs/tiny.config b/kernel/configs/tiny.config
index 8a44b93da0f3..c2f9c912df1c 100644
--- a/kernel/configs/tiny.config
+++ b/kernel/configs/tiny.config
@@ -7,5 +7,6 @@ CONFIG_KERNEL_XZ=y
# CONFIG_KERNEL_LZO is not set
# CONFIG_KERNEL_LZ4 is not set
# CONFIG_SLAB is not set
-# CONFIG_SLUB is not set
-CONFIG_SLOB=y
+# CONFIG_SLOB_DEPRECATED is not set
+CONFIG_SLUB=y
+CONFIG_SLUB_TINY=y
diff --git a/mm/Kconfig b/mm/Kconfig
index 5941cb34e30d..dcc49c69552f 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -219,17 +219,30 @@ config SLUB
and has enhanced diagnostics. SLUB is the default choice for
a slab allocator.

-config SLOB
+config SLOB_DEPRECATED
depends on EXPERT
- bool "SLOB (Simple Allocator)"
+ bool "SLOB (Simple Allocator - DEPRECATED)"
depends on !PREEMPT_RT
help
+ Deprecated and scheduled for removal in a few cycles. SLUB
+ recommended as replacement. CONFIG_SLUB_TINY can be considered
+ on systems with 16MB or less RAM.
+
+ If you need SLOB to stay, please contact linux-mm@xxxxxxxxx and
+ people listed in the SLAB ALLOCATOR section of MAINTAINERS file,
+ with your use case.
+
SLOB replaces the stock allocator with a drastically simpler
allocator. SLOB is generally more space efficient but
does not perform as well on large systems.

endchoice

+config SLOB
+ bool
+ default y
+ depends on SLOB_DEPRECATED
+
config SLUB_TINY
bool "Configure SLUB for minimal memory footprint"
depends on SLUB && EXPERT

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Next in thread: Damien Le Moal: "Re: [PATCH 12/12] mm, slob: rename CONFIG_SLOB to CONFIG_SLOB_DEPRECATED"
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