Date:   Fri, 02 Dec 2022 09:59:19 -0800 (PST)
From:   Palmer Dabbelt <palmer@...belt.com>
To:     vbabka@...e.cz, damien.lemoal@...nsource.wdc.com
CC:     cl@...ux.com, rientjes@...gle.com, iamjoonsoo.kim@....com,
        penberg@...nel.org, 42.hyeyoo@...il.com, roman.gushchin@...ux.dev,
        akpm@...ux-foundation.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        willy@...radead.org, patches@...ts.linux.dev, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, vbabka@...e.cz,
        linux@...linux.org.uk, aaro.koskinen@....fi, jmkrzyszt@...il.com,
        tony@...mide.com, jonas@...thpole.se,
        stefan.kristiansson@...nalahti.fi, shorne@...il.com,
        ysato@...rs.sourceforge.jp, dalias@...c.org,
        Arnd Bergmann <arnd@...db.de>, josh@...htriplett.org,
        Conor Dooley <conor@...nel.org>, christophe.leroy@...roup.eu,
        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 Mon, 21 Nov 2022 09:12:02 PST (-0800), vbabka@...e.cz 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.
>
> [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>
> ---
>  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@...osinc.com>

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@...ck.org 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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