Re: [PATCH v2 02/21] mm/slab: remove CONFIG_SLAB from all Kconfig and Makefile

Hyeonggon Yoo
2023-12-05T04:15:53Z

On Mon, Nov 20, 2023 at 07:34:13PM +0100, Vlastimil Babka wrote:
> Remove CONFIG_SLAB, CONFIG_DEBUG_SLAB, CONFIG_SLAB_DEPRECATED and
> everything in Kconfig files and mm/Makefile that depends on those. Since
> SLUB is the only remaining allocator, remove the allocator choice, make
> CONFIG_SLUB a "def_bool y" for now and remove all explicit dependencies
> on SLUB or SLAB as it's now always enabled. Make every option's verbose
> name and description refer to "the slab allocator" without refering to
> the specific implementation. Do not rename the CONFIG_ option names yet.
>
> Everything under #ifdef CONFIG_SLAB, and mm/slab.c is now dead code, all
> code under #ifdef CONFIG_SLUB is now always compiled.
>
> Reviewed-by: Kees Cook <keescook@chromium.org>
> Reviewed-by: Christoph Lameter <cl@linux.com>
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
> ---
> arch/arm64/Kconfig | 2 +-
> arch/s390/Kconfig | 2 +-
> arch/x86/Kconfig | 2 +-
> lib/Kconfig.debug | 1 -
> lib/Kconfig.kasan | 11 +++------
> lib/Kconfig.kfence | 2 +-
> lib/Kconfig.kmsan | 2 +-
> mm/Kconfig | 68 ++++++++++++------------------------------------------
> mm/Kconfig.debug | 16 ++++---------
> mm/Makefile | 6 +----
> 10 files changed, 28 insertions(+), 84 deletions(-)
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 7b071a00425d..325b7140b576 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -154,7 +154,7 @@ config ARM64
> select HAVE_MOVE_PUD
> select HAVE_PCI
> select HAVE_ACPI_APEI if (ACPI && EFI)
> - select HAVE_ALIGNED_STRUCT_PAGE if SLUB
> + select HAVE_ALIGNED_STRUCT_PAGE
> select HAVE_ARCH_AUDITSYSCALL
> select HAVE_ARCH_BITREVERSE
> select HAVE_ARCH_COMPILER_H
> diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
> index 3bec98d20283..afa42a6f2e09 100644
> --- a/arch/s390/Kconfig
> +++ b/arch/s390/Kconfig
> @@ -146,7 +146,7 @@ config S390
> select GENERIC_TIME_VSYSCALL
> select GENERIC_VDSO_TIME_NS
> select GENERIC_IOREMAP if PCI
> - select HAVE_ALIGNED_STRUCT_PAGE if SLUB
> + select HAVE_ALIGNED_STRUCT_PAGE
> select HAVE_ARCH_AUDITSYSCALL
> select HAVE_ARCH_JUMP_LABEL
> select HAVE_ARCH_JUMP_LABEL_RELATIVE
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 3762f41bb092..3f460f334d4e 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -169,7 +169,7 @@ config X86
> select HAS_IOPORT
> select HAVE_ACPI_APEI if ACPI
> select HAVE_ACPI_APEI_NMI if ACPI
> - select HAVE_ALIGNED_STRUCT_PAGE if SLUB
> + select HAVE_ALIGNED_STRUCT_PAGE
> select HAVE_ARCH_AUDITSYSCALL
> select HAVE_ARCH_HUGE_VMAP if X86_64 || X86_PAE
> select HAVE_ARCH_HUGE_VMALLOC if X86_64
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index cc7d53d9dc01..e1765face106 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -1985,7 +1985,6 @@ config FAULT_INJECTION
> config FAILSLAB
> bool "Fault-injection capability for kmalloc"
> depends on FAULT_INJECTION
> - depends on SLAB || SLUB
> help
> Provide fault-injection capability for kmalloc.
>
> diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
> index fdca89c05745..97e1fdbb5910 100644
> --- a/lib/Kconfig.kasan
> +++ b/lib/Kconfig.kasan
> @@ -37,7 +37,7 @@ menuconfig KASAN
> (HAVE_ARCH_KASAN_SW_TAGS && CC_HAS_KASAN_SW_TAGS)) && \
> CC_HAS_WORKING_NOSANITIZE_ADDRESS) || \
> HAVE_ARCH_KASAN_HW_TAGS
> - depends on (SLUB && SYSFS && !SLUB_TINY) || (SLAB && !DEBUG_SLAB)
> + depends on SYSFS && !SLUB_TINY
> select STACKDEPOT_ALWAYS_INIT
> help
> Enables KASAN (Kernel Address Sanitizer) - a dynamic memory safety
> @@ -78,7 +78,7 @@ config KASAN_GENERIC
> bool "Generic KASAN"
> depends on HAVE_ARCH_KASAN && CC_HAS_KASAN_GENERIC
> depends on CC_HAS_WORKING_NOSANITIZE_ADDRESS
> - select SLUB_DEBUG if SLUB
> + select SLUB_DEBUG
> select CONSTRUCTORS
> help
> Enables Generic KASAN.
> @@ -89,13 +89,11 @@ config KASAN_GENERIC
> overhead of ~50% for dynamic allocations.
> The performance slowdown is ~x3.
>
> - (Incompatible with CONFIG_DEBUG_SLAB: the kernel does not boot.)
> -
> config KASAN_SW_TAGS
> bool "Software Tag-Based KASAN"
> depends on HAVE_ARCH_KASAN_SW_TAGS && CC_HAS_KASAN_SW_TAGS
> depends on CC_HAS_WORKING_NOSANITIZE_ADDRESS
> - select SLUB_DEBUG if SLUB
> + select SLUB_DEBUG
> select CONSTRUCTORS
> help
> Enables Software Tag-Based KASAN.
> @@ -110,12 +108,9 @@ config KASAN_SW_TAGS
> May potentially introduce problems related to pointer casting and
> comparison, as it embeds a tag into the top byte of each pointer.
>
> - (Incompatible with CONFIG_DEBUG_SLAB: the kernel does not boot.)
> -
> config KASAN_HW_TAGS
> bool "Hardware Tag-Based KASAN"
> depends on HAVE_ARCH_KASAN_HW_TAGS
> - depends on SLUB
> help
> Enables Hardware Tag-Based KASAN.
>
> diff --git a/lib/Kconfig.kfence b/lib/Kconfig.kfence
> index 459dda9ef619..6fbbebec683a 100644
> --- a/lib/Kconfig.kfence
> +++ b/lib/Kconfig.kfence
> @@ -5,7 +5,7 @@ config HAVE_ARCH_KFENCE
>
> menuconfig KFENCE
> bool "KFENCE: low-overhead sampling-based memory safety error detector"
> - depends on HAVE_ARCH_KFENCE && (SLAB || SLUB)
> + depends on HAVE_ARCH_KFENCE
> select STACKTRACE
> select IRQ_WORK
> help
> diff --git a/lib/Kconfig.kmsan b/lib/Kconfig.kmsan
> index ef2c8f256c57..0541d7b079cc 100644
> --- a/lib/Kconfig.kmsan
> +++ b/lib/Kconfig.kmsan
> @@ -11,7 +11,7 @@ config HAVE_KMSAN_COMPILER
> config KMSAN
> bool "KMSAN: detector of uninitialized values use"
> depends on HAVE_ARCH_KMSAN && HAVE_KMSAN_COMPILER
> - depends on SLUB && DEBUG_KERNEL && !KASAN && !KCSAN
> + depends on DEBUG_KERNEL && !KASAN && !KCSAN
> depends on !PREEMPT_RT
> select STACKDEPOT
> select STACKDEPOT_ALWAYS_INIT
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 89971a894b60..4636870499bb 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -226,52 +226,17 @@ config ZSMALLOC_CHAIN_SIZE
>
> For more information, see zsmalloc documentation.
>
> -menu "SLAB allocator options"
> -
> -choice
> - prompt "Choose SLAB allocator"
> - default SLUB
> - help
> - This option allows to select a slab allocator.
> -
> -config SLAB_DEPRECATED
> - bool "SLAB (DEPRECATED)"
> - depends on !PREEMPT_RT
> - help
> - Deprecated and scheduled for removal in a few cycles. Replaced by
> - SLUB.
> -
> - If you cannot migrate to SLUB, please contact linux-mm@kvack.org
> - and the people listed in the SLAB ALLOCATOR section of MAINTAINERS
> - file, explaining why.
> -
> - The regular slab allocator that is established and known to work
> - well in all environments. It organizes cache hot objects in
> - per cpu and per node queues.
> +menu "Slab allocator options"
>
> config SLUB
> - bool "SLUB (Unqueued Allocator)"
> - help
> - SLUB is a slab allocator that minimizes cache line usage
> - instead of managing queues of cached objects (SLAB approach).
> - Per cpu caching is realized using slabs of objects instead
> - of queues of objects. SLUB can use memory efficiently
> - and has enhanced diagnostics. SLUB is the default choice for
> - a slab allocator.
> -
> -endchoice
> -
> -config SLAB
> - bool
> - default y
> - depends on SLAB_DEPRECATED
> + def_bool y
>
> config SLUB_TINY
> - bool "Configure SLUB for minimal memory footprint"
> - depends on SLUB && EXPERT
> + bool "Configure for minimal memory footprint"
> + depends on EXPERT
> select SLAB_MERGE_DEFAULT
> help
> - Configures the SLUB allocator in a way to achieve minimal memory
> + Configures the slab allocator in a way to achieve minimal memory
> footprint, sacrificing scalability, debugging and other features.
> This is intended only for the smallest system that had used the
> SLOB allocator and is not recommended for systems with more than
> @@ -282,7 +247,6 @@ config SLUB_TINY
> config SLAB_MERGE_DEFAULT
> bool "Allow slab caches to be merged"
> default y
> - depends on SLAB || SLUB
> help
> For reduced kernel memory fragmentation, slab caches can be
> merged when they share the same size and other characteristics.
> @@ -296,7 +260,7 @@ config SLAB_MERGE_DEFAULT
>
> config SLAB_FREELIST_RANDOM
> bool "Randomize slab freelist"
> - depends on SLAB || (SLUB && !SLUB_TINY)
> + depends on !SLUB_TINY
> help
> Randomizes the freelist order used on creating new pages. This
> security feature reduces the predictability of the kernel slab
> @@ -304,21 +268,19 @@ config SLAB_FREELIST_RANDOM
>
> config SLAB_FREELIST_HARDENED
> bool "Harden slab freelist metadata"
> - depends on SLAB || (SLUB && !SLUB_TINY)
> + depends on !SLUB_TINY
> help
> Many kernel heap attacks try to target slab cache metadata and
> other infrastructure. This options makes minor performance
> sacrifices to harden the kernel slab allocator against common
> - freelist exploit methods. Some slab implementations have more
> - sanity-checking than others. This option is most effective with
> - CONFIG_SLUB.
> + freelist exploit methods.
>
> config SLUB_STATS
> default n
> - bool "Enable SLUB performance statistics"
> - depends on SLUB && SYSFS && !SLUB_TINY
> + bool "Enable performance statistics"
> + depends on SYSFS && !SLUB_TINY
> help
> - SLUB statistics are useful to debug SLUBs allocation behavior in
> + The statistics are useful to debug slab allocation behavior in
> order find ways to optimize the allocator. This should never be
> enabled for production use since keeping statistics slows down
> the allocator by a few percentage points. The slabinfo command
> @@ -328,8 +290,8 @@ config SLUB_STATS
>
> config SLUB_CPU_PARTIAL
> default y
> - depends on SLUB && SMP && !SLUB_TINY
> - bool "SLUB per cpu partial cache"
> + depends on SMP && !SLUB_TINY
> + bool "Enable per cpu partial caches"
> help
> Per cpu partial caches accelerate objects allocation and freeing
> that is local to a processor at the price of more indeterminism
> @@ -339,7 +301,7 @@ config SLUB_CPU_PARTIAL
>
> config RANDOM_KMALLOC_CACHES
> default n
> - depends on SLUB && !SLUB_TINY
> + depends on !SLUB_TINY
> bool "Randomize slab caches for normal kmalloc"
> help
> A hardening feature that creates multiple copies of slab caches for
> @@ -354,7 +316,7 @@ config RANDOM_KMALLOC_CACHES
> limited degree of memory and CPU overhead that relates to hardware and
> system workload.
>
> -endmenu # SLAB allocator options
> +endmenu # Slab allocator options
>
> config SHUFFLE_PAGE_ALLOCATOR
> bool "Page allocator randomization"
> diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
> index 018a5bd2f576..321ab379994f 100644
> --- a/mm/Kconfig.debug
> +++ b/mm/Kconfig.debug
> @@ -45,18 +45,10 @@ config DEBUG_PAGEALLOC_ENABLE_DEFAULT
> Enable debug page memory allocations by default? This value
> can be overridden by debug_pagealloc=off|on.
>
> -config DEBUG_SLAB
> - bool "Debug slab memory allocations"
> - depends on DEBUG_KERNEL && SLAB
> - help
> - Say Y here to have the kernel do limited verification on memory
> - allocation as well as poisoning memory on free to catch use of freed
> - memory. This can make kmalloc/kfree-intensive workloads much slower.
> -
> config SLUB_DEBUG
> default y
> bool "Enable SLUB debugging support" if EXPERT
> - depends on SLUB && SYSFS && !SLUB_TINY
> + depends on SYSFS && !SLUB_TINY
> select STACKDEPOT if STACKTRACE_SUPPORT
> help
> SLUB has extensive debug support features. Disabling these can
> @@ -66,7 +58,7 @@ config SLUB_DEBUG
>
> config SLUB_DEBUG_ON
> bool "SLUB debugging on by default"
> - depends on SLUB && SLUB_DEBUG
> + depends on SLUB_DEBUG
> select STACKDEPOT_ALWAYS_INIT if STACKTRACE_SUPPORT
> default n
> help
> @@ -231,8 +223,8 @@ config DEBUG_KMEMLEAK
> allocations. See Documentation/dev-tools/kmemleak.rst for more
> details.
>
> - Enabling DEBUG_SLAB or SLUB_DEBUG may increase the chances
> - of finding leaks due to the slab objects poisoning.
> + Enabling SLUB_DEBUG may increase the chances of finding leaks
> + due to the slab objects poisoning.
>
> In order to access the kmemleak file, debugfs needs to be
> mounted (usually at /sys/kernel/debug).
> diff --git a/mm/Makefile b/mm/Makefile
> index 33873c8aedb3..e4b5b75aaec9 100644
> --- a/mm/Makefile
> +++ b/mm/Makefile
> @@ -4,7 +4,6 @@
> #
>
> KASAN_SANITIZE_slab_common.o := n
> -KASAN_SANITIZE_slab.o := n
> KASAN_SANITIZE_slub.o := n
> KCSAN_SANITIZE_kmemleak.o := n
>
> @@ -12,7 +11,6 @@ KCSAN_SANITIZE_kmemleak.o := n
> # the same word but accesses to different bits of that word. Re-enable KCSAN
> # for these when we have more consensus on what to do about them.
> KCSAN_SANITIZE_slab_common.o := n
> -KCSAN_SANITIZE_slab.o := n
> KCSAN_SANITIZE_slub.o := n
> KCSAN_SANITIZE_page_alloc.o := n
> # But enable explicit instrumentation for memory barriers.
> @@ -22,7 +20,6 @@ KCSAN_INSTRUMENT_BARRIERS := y
> # flaky coverage that is not a function of syscall inputs. E.g. slab is out of
> # free pages, or a task is migrated between nodes.
> KCOV_INSTRUMENT_slab_common.o := n
> -KCOV_INSTRUMENT_slab.o := n
> KCOV_INSTRUMENT_slub.o := n
> KCOV_INSTRUMENT_page_alloc.o := n
> KCOV_INSTRUMENT_debug-pagealloc.o := n
> @@ -66,6 +63,7 @@ obj-y += page-alloc.o
> obj-y += init-mm.o
> obj-y += memblock.o
> obj-y += $(memory-hotplug-y)
> +obj-y += slub.o
>
> ifdef CONFIG_MMU
> obj-$(CONFIG_ADVISE_SYSCALLS) += madvise.o
> @@ -82,8 +80,6 @@ obj-$(CONFIG_SPARSEMEM_VMEMMAP) += sparse-vmemmap.o
> obj-$(CONFIG_MMU_NOTIFIER) += mmu_notifier.o
> obj-$(CONFIG_KSM) += ksm.o
> obj-$(CONFIG_PAGE_POISONING) += page_poison.o
> -obj-$(CONFIG_SLAB) += slab.o
> -obj-$(CONFIG_SLUB) += slub.o
> obj-$(CONFIG_KASAN) += kasan/
> obj-$(CONFIG_KFENCE) += kfence/
> obj-$(CONFIG_KMSAN) += kmsan/

Looks good to me,
Reviewed-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>

Nit:

- Some arch configs enables DEBUG_SLAB
- Some documentations refers to {DEBUG_,}SLAB config (i.e. "enable
DEBUG_SLAB for debugging", or "use SLUB instead of SLAB for reducing OS
jitter", ... etc)
- fs/orangefs/orangefs-kernel.h uses #if (defined CONFIG_DEBUG_SLAB)

$ git grep DEBUG_SLAB arch/
arch/arm/configs/ep93xx_defconfig:CONFIG_DEBUG_SLAB=y
arch/arm/configs/tegra_defconfig:CONFIG_DEBUG_SLAB=y
arch/microblaze/configs/mmu_defconfig:CONFIG_DEBUG_SLAB=y

$ git grep SLAB Documentation/

[... some unrelated lines removed ...]

Documentation/admin-guide/cgroup-v1/cpusets.rst:PFA_SPREAD_SLAB, and appropriately marked slab caches will allocate
Documentation/admin-guide/cgroup-v1/memory.rst: pages allocated by the SLAB or SLUB allocator are tracked. A copy
Documentation/admin-guide/kernel-per-CPU-kthreads.rst: CONFIG_SLAB=y, thus avoiding the slab allocator's periodic
Documentation/admin-guide/mm/pagemap.rst: The page is managed by the SLAB/SLUB kernel memory allocator.
Documentation/dev-tools/kasan.rst:For slab, both software KASAN modes support SLUB and SLAB allocators, while
Documentation/dev-tools/kfence.rst:of the sample interval, the next allocation through the main allocator (SLAB or
Documentation/mm/slub.rst:The basic philosophy of SLUB is very different from SLAB. SLAB
Documentation/mm/slub.rst: Sorry SLAB legacy issues)
Documentation/process/4.Coding.rst: - DEBUG_SLAB can find a variety of memory allocation and use errors; it
Documentation/process/submit-checklist.rst: ``CONFIG_DEBUG_SLAB``, ``CONFIG_DEBUG_PAGEALLOC``, ``CONFIG_DEBUG_MUTEXES``,
Documentation/scsi/ChangeLog.lpfc: CONFIG_DEBUG_SLAB set).
Documentation/translations/it_IT/process/4.Coding.rst: - DEBUG_SLAB può trovare svariati errori di uso e di allocazione di memoria;
Documentation/translations/it_IT/process/submit-checklist.rst: ``CONFIG_DEBUG_SLAB``, ``CONFIG_DEBUG_PAGEALLOC``, ``CONFIG_DEBUG_MUTEXES``,
Documentation/translations/ja_JP/SubmitChecklist:12: CONFIG_PREEMPT, CONFIG_DEBUG_PREEMPT, CONFIG_DEBUG_SLAB,
Documentation/translations/zh_CN/dev-tools/kasan.rst:对于slab，两种软件KASAN模式都支持SLUB和SLAB分配器，而基于硬件标签的
Documentation/translations/zh_CN/process/4.Coding.rst: - DEBUG_SLAB 可以发现各种内存分配和使用错误；它应该用于大多数开发内核。
Documentation/translations/zh_CN/process/submit-checklist.rst: ``CONFIG_DEBUG_SLAB``, ``CONFIG_DEBUG_PAGEALLOC``, ``CONFIG_DEBUG_MUTEXES``,
Documentation/translations/zh_TW/dev-tools/kasan.rst:對於slab，兩種軟件KASAN模式都支持SLUB和SLAB分配器，而基於硬件標籤的
Documentation/translations/zh_TW/process/4.Coding.rst: - DEBUG_SLAB 可以發現各種內存分配和使用錯誤；它應該用於大多數開發內核。
Documentation/translations/zh_TW/process/submit-checklist.rst: ``CONFIG_DEBUG_SLAB``, ``CONFIG_DEBUG_PAGEALLOC``, ``CONFIG_DEBUG_MUTEXES``,

--
Hyeonggon