[PATCH RFC 8/8] mm, slab: deprecate CONFIG_SLUB_TINY and reduce its Kconfig effects

[Vlastimil Babka (SUSE)]

At this point CONFIG_SLUB_TINY only affects the default value of
slab_tiny_enabled which has a boot-time parameter. Thus deprecate it in
the Kconfig description.

Also remove its interactions with other Kconfig option, as they are not
necessary:

- KASAN, SLUB_DEBUG or SLUB_STATS support does not need !SLUB_TINY

- KVFREE_RCU_BATCHED can simply depend on !TINY_RCU

- various hardening options do not need to be excluded, although it's
  unlikely that somebody would enable those with extra memory overhead
  together with slab_tiny

- SLAB_MERGE_DEFAULT does not need to be selected, although it's likely
  to be used together

Keep the "depends on EXPERT && !COMPILE_TEST" as there's no point making
the deprecated option more visible.

Signed-off-by: Vlastimil Babka (SUSE) <vbabka@xxxxxxxxxx>
---
 lib/Kconfig.kasan |  2 +-
 mm/Kconfig        | 16 +++++++---------
 mm/Kconfig.debug  |  2 +-
 3 files changed, 9 insertions(+), 11 deletions(-)

diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
index a4bb610a7a6f..f20b574f6653 100644
--- a/lib/Kconfig.kasan
+++ b/lib/Kconfig.kasan
@@ -49,7 +49,7 @@ menuconfig KASAN
 		     (HAVE_ARCH_KASAN_SW_TAGS && CC_HAS_KASAN_SW_TAGS)) && \
 		    CC_HAS_WORKING_NOSANITIZE_ADDRESS) || \
 		   HAVE_ARCH_KASAN_HW_TAGS
-	depends on SYSFS && !SLUB_TINY
+	depends on SYSFS
 	select STACKDEPOT_ALWAYS_INIT
 	help
 	  Enables KASAN (Kernel Address Sanitizer) - a dynamic memory safety
diff --git a/mm/Kconfig b/mm/Kconfig
index 604c58199acb..a1b1ff7db59f 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -167,16 +167,18 @@ config SLUB
 
 config KVFREE_RCU_BATCHED
 	def_bool y
-	depends on !SLUB_TINY && !TINY_RCU
+	depends on !TINY_RCU
 	depends on !RCU_STRICT_GRACE_PERIOD
 
 config SLUB_TINY
-	bool "Configure for minimal memory footprint"
+	bool "Enable slab_tiny by default"
 	depends on EXPERT && !COMPILE_TEST
-	select SLAB_MERGE_DEFAULT
 	help
+	   Deprecated option that enables the slab_tiny boot parameter by
+	   default, and can be overridden by booting with slab_tiny=0.
+
 	   Configures the slab allocator in a way to achieve minimal memory
-	   footprint, sacrificing scalability, debugging and other features.
+	   footprint, sacrificing scalability.
 	   This is intended only for the smallest system that had used the
 	   SLOB allocator and is not recommended for systems with more than
 	   16MB RAM.
@@ -199,7 +201,6 @@ config SLAB_MERGE_DEFAULT
 
 config SLAB_FREELIST_RANDOM
 	bool "Randomize slab freelist"
-	depends on !SLUB_TINY
 	help
 	  Randomizes the freelist order used on creating new pages. This
 	  security feature reduces the predictability of the kernel slab
@@ -207,7 +208,6 @@ config SLAB_FREELIST_RANDOM
 
 config SLAB_FREELIST_HARDENED
 	bool "Harden slab freelist metadata"
-	depends on !SLUB_TINY
 	help
 	  Many kernel heap attacks try to target slab cache metadata and
 	  other infrastructure. This options makes minor performance
@@ -216,7 +216,6 @@ config SLAB_FREELIST_HARDENED
 
 config SLAB_BUCKETS
 	bool "Support allocation from separate kmalloc buckets"
-	depends on !SLUB_TINY
 	default SLAB_FREELIST_HARDENED
 	help
 	  Kernel heap attacks frequently depend on being able to create
@@ -234,7 +233,7 @@ config SLAB_BUCKETS
 config SLUB_STATS
 	default n
 	bool "Enable performance statistics"
-	depends on SYSFS && !SLUB_TINY
+	depends on SYSFS
 	help
 	  The statistics are useful to debug slab allocation behavior in
 	  order find ways to optimize the allocator. This should never be
@@ -245,7 +244,6 @@ config SLUB_STATS
 	  Try running: slabinfo -DA
 
 config KMALLOC_PARTITION_CACHES
-	depends on !SLUB_TINY
 	bool "Partitioned slab caches for normal kmalloc"
 	default RANDOM_KMALLOC_CACHES
 	help
diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
index 15dca19dd07d..7fa01e48c9f0 100644
--- a/mm/Kconfig.debug
+++ b/mm/Kconfig.debug
@@ -48,7 +48,7 @@ config DEBUG_PAGEALLOC_ENABLE_DEFAULT
 config SLUB_DEBUG
 	default y
 	bool "Enable SLUB debugging support" if EXPERT
-	depends on SYSFS && !SLUB_TINY
+	depends on SYSFS
 	select STACKDEPOT if STACKTRACE_SUPPORT
 	help
 	  SLUB has extensive debug support features. Disabling these can

-- 
2.55.0