mm/slab: remove CONFIG_SLAB from all Kconfig and Makefile

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>
Acked-by: David Rientjes <rientjes@google.com>
Tested-by: David Rientjes <rientjes@google.com>
Reviewed-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Tested-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>

3 files changed, 20 insertions, 70 deletions

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/