Merge tag 'slab-for-6.4' of git://git.kernel.org/pub/scm/linux/kernel/git/vbabka/slab

Pull slab updates from Vlastimil Babka:
 "The main change is naturally the SLOB removal. Since its deprecation
  in 6.2 I've seen no complaints so hopefully SLUB_(TINY) works well for
  everyone and we can proceed.

  Besides the code cleanup, the main immediate benefit will be allowing
  kfree() family of function to work on kmem_cache_alloc() objects,
  which was incompatible with SLOB. This includes kfree_rcu() which had
  no kmem_cache_free_rcu() counterpart yet and now it shouldn't be
  necessary anymore.

  Besides that, there are several small code and comment improvements
  from Thomas, Thorsten and Vernon"

* tag 'slab-for-6.4' of git://git.kernel.org/pub/scm/linux/kernel/git/vbabka/slab:
  mm/slab: document kfree() as allowed for kmem_cache_alloc() objects
  mm/slob: remove slob.c
  mm/slab: remove CONFIG_SLOB code from slab common code
  mm, pagemap: remove SLOB and SLQB from comments and documentation
  mm, page_flags: remove PG_slob_free
  mm/slob: remove CONFIG_SLOB
  mm/slub: fix help comment of SLUB_DEBUG
  mm: slub: make kobj_type structure constant
  slab: Adjust comment after refactoring of gfp.h

Author: torvalds

Documentation/admin-guide/mm/pagemap.rst

@@ -91,9 +91,9 @@ Short descriptions to the page flags
    The page is being locked for exclusive access, e.g. by undergoing read/write
    IO.
 7 - SLAB
-   The page is managed by the SLAB/SLOB/SLUB/SLQB kernel memory allocator.
-   When compound page is used, SLUB/SLQB will only set this flag on the head
-   page; SLOB will not flag it at all.
+   The page is managed by the SLAB/SLUB kernel memory allocator.
+   When compound page is used, either will only set this flag on the head
+   page.
 10 - BUDDY
     A free memory block managed by the buddy system allocator.
     The buddy system organizes free memory in blocks of various orders.

Documentation/core-api/memory-allocation.rst

@@ -170,7 +170,16 @@ should be used if a part of the cache might be copied to the userspace.
 After the cache is created kmem_cache_alloc() and its convenience
 wrappers can allocate memory from that cache.
 
-When the allocated memory is no longer needed it must be freed. You can
-use kvfree() for the memory allocated with `kmalloc`, `vmalloc` and
-`kvmalloc`. The slab caches should be freed with kmem_cache_free(). And
-don't forget to destroy the cache with kmem_cache_destroy().
+When the allocated memory is no longer needed it must be freed.
+
+Objects allocated by `kmalloc` can be freed by `kfree` or `kvfree`. Objects
+allocated by `kmem_cache_alloc` can be freed with `kmem_cache_free`, `kfree`
+or `kvfree`, where the latter two might be more convenient thanks to not
+needing the kmem_cache pointer.
+
+The same rules apply to _bulk and _rcu flavors of freeing functions.
+
+Memory allocated by `vmalloc` can be freed with `vfree` or `kvfree`.
+Memory allocated by `kvmalloc` can be freed with `kvfree`.
+Caches created by `kmem_cache_create` should be freed with
+`kmem_cache_destroy` only after freeing all the allocated objects first.

fs/proc/page.c

@@ -125,7 +125,7 @@ u64 stable_page_flags(struct page *page)
 	/*
 	 * pseudo flags for the well known (anonymous) memory mapped pages
 	 *
-	 * Note that page->_mapcount is overloaded in SLOB/SLUB/SLQB, so the
+	 * Note that page->_mapcount is overloaded in SLAB, so the
 	 * simple test in page_mapped() is not enough.
 	 */
 	if (!PageSlab(page) && page_mapped(page))
@@ -165,9 +165,8 @@ u64 stable_page_flags(struct page *page)
 
 
 	/*
-	 * Caveats on high order pages: page->_refcount will only be set
-	 * -1 on the head page; SLUB/SLQB do the same for PG_slab;
-	 * SLOB won't set PG_slab at all on compound pages.
+	 * Caveats on high order pages: PG_buddy and PG_slab will only be set
+	 * on the head page.
 	 */
 	if (PageBuddy(page))
 		u |= 1 << KPF_BUDDY;
@@ -185,7 +184,7 @@ u64 stable_page_flags(struct page *page)
 	u |= kpf_copy_bit(k, KPF_LOCKED,	PG_locked);
 
 	u |= kpf_copy_bit(k, KPF_SLAB,		PG_slab);
-	if (PageTail(page) && PageSlab(compound_head(page)))
+	if (PageTail(page) && PageSlab(page))
 		u |= 1 << KPF_SLAB;
 
 	u |= kpf_copy_bit(k, KPF_ERROR,		PG_error);

include/linux/page-flags.h

@@ -174,9 +174,6 @@ enum pageflags {
 	/* Remapped by swiotlb-xen. */
 	PG_xen_remapped = PG_owner_priv_1,
 
-	/* SLOB */
-	PG_slob_free = PG_private,
-
 #ifdef CONFIG_MEMORY_FAILURE
 	/*
 	 * Compound pages. Stored in first tail page's flags.
@@ -483,7 +480,6 @@ PAGEFLAG(Active, active, PF_HEAD) __CLEARPAGEFLAG(Active, active, PF_HEAD)
 PAGEFLAG(Workingset, workingset, PF_HEAD)
 	TESTCLEARFLAG(Workingset, workingset, PF_HEAD)
 __PAGEFLAG(Slab, slab, PF_NO_TAIL)
-__PAGEFLAG(SlobFree, slob_free, PF_NO_TAIL)
 PAGEFLAG(Checked, checked, PF_NO_COMPOUND)	   /* Used by some filesystems */
 
 /* Xen */

include/linux/rcupdate.h

@@ -976,8 +976,10 @@ static inline notrace void rcu_read_unlock_sched_notrace(void)
  * either fall back to use of call_rcu() or rearrange the structure to
  * position the rcu_head structure into the first 4096 bytes.
  *
- * Note that the allowable offset might decrease in the future, for example,
- * to allow something like kmem_cache_free_rcu().
+ * The object to be freed can be allocated either by kmalloc() or
+ * kmem_cache_alloc().
+ *
+ * Note that the allowable offset might decrease in the future.
  *
  * The BUILD_BUG_ON check must not involve any function calls, hence the
  * checks are done in macros here.

include/linux/slab.h

@@ -298,19 +298,6 @@ static inline unsigned int arch_slab_minalign(void)
 #endif
 #endif
 
-#ifdef CONFIG_SLOB
-/*
- * SLOB passes all requests larger than one page to the page allocator.
- * No kmalloc array is necessary since objects of different sizes can
- * be allocated from the same page.
- */
-#define KMALLOC_SHIFT_HIGH	PAGE_SHIFT
-#define KMALLOC_SHIFT_MAX	(MAX_ORDER + PAGE_SHIFT - 1)
-#ifndef KMALLOC_SHIFT_LOW
-#define KMALLOC_SHIFT_LOW	3
-#endif
-#endif
-
 /* Maximum allocatable size */
 #define KMALLOC_MAX_SIZE	(1UL << KMALLOC_SHIFT_MAX)
 /* Maximum size for which we actually use a slab cache */
@@ -366,7 +353,6 @@ enum kmalloc_cache_type {
 	NR_KMALLOC_TYPES
 };
 
-#ifndef CONFIG_SLOB
 extern struct kmem_cache *
 kmalloc_caches[NR_KMALLOC_TYPES][KMALLOC_SHIFT_HIGH + 1];
 
@@ -458,7 +444,6 @@ static __always_inline unsigned int __kmalloc_index(size_t size,
 }
 static_assert(PAGE_SHIFT <= 20);
 #define kmalloc_index(s) __kmalloc_index(s, true)
-#endif /* !CONFIG_SLOB */
 
 void *__kmalloc(size_t size, gfp_t flags) __assume_kmalloc_alignment __alloc_size(1);
 
@@ -487,10 +472,6 @@ void kmem_cache_free(struct kmem_cache *s, void *objp);
 void kmem_cache_free_bulk(struct kmem_cache *s, size_t size, void **p);
 int kmem_cache_alloc_bulk(struct kmem_cache *s, gfp_t flags, size_t size, void **p);
 
-/*
- * Caller must not use kfree_bulk() on memory not originally allocated
- * by kmalloc(), because the SLOB allocator cannot handle this.
- */
 static __always_inline void kfree_bulk(size_t size, void **p)
 {
 	kmem_cache_free_bulk(NULL, size, p);
@@ -526,7 +507,7 @@ void *kmalloc_large_node(size_t size, gfp_t flags, int node) __assume_page_align
  * to be at least to the size.
  *
  * The @flags argument may be one of the GFP flags defined at
- * include/linux/gfp.h and described at
+ * include/linux/gfp_types.h and described at
  * :ref:`Documentation/core-api/mm-api.rst <mm-api-gfp-flags>`
  *
  * The recommended usage of the @flags is described at
@@ -567,7 +548,6 @@ void *kmalloc_large_node(size_t size, gfp_t flags, int node) __assume_page_align
  *	Try really hard to succeed the allocation but fail
  *	eventually.
  */
-#ifndef CONFIG_SLOB
 static __always_inline __alloc_size(1) void *kmalloc(size_t size, gfp_t flags)
 {
 	if (__builtin_constant_p(size) && size) {
@@ -583,17 +563,7 @@ static __always_inline __alloc_size(1) void *kmalloc(size_t size, gfp_t flags)
 	}
 	return __kmalloc(size, flags);
 }
-#else
-static __always_inline __alloc_size(1) void *kmalloc(size_t size, gfp_t flags)
-{
-	if (__builtin_constant_p(size) && size > KMALLOC_MAX_CACHE_SIZE)
-		return kmalloc_large(size, flags);
-
-	return __kmalloc(size, flags);
-}
-#endif
 
-#ifndef CONFIG_SLOB
 static __always_inline __alloc_size(1) void *kmalloc_node(size_t size, gfp_t flags, int node)
 {
 	if (__builtin_constant_p(size) && size) {
@@ -609,15 +579,6 @@ static __always_inline __alloc_size(1) void *kmalloc_node(size_t size, gfp_t fla
 	}
 	return __kmalloc_node(size, flags, node);
 }
-#else
-static __always_inline __alloc_size(1) void *kmalloc_node(size_t size, gfp_t flags, int node)
-{
-	if (__builtin_constant_p(size) && size > KMALLOC_MAX_CACHE_SIZE)
-		return kmalloc_large_node(size, flags, node);
-
-	return __kmalloc_node(size, flags, node);
-}
-#endif
 
 /**
  * kmalloc_array - allocate memory for an array.

init/Kconfig

@@ -945,7 +945,7 @@ config MEMCG
 
 config MEMCG_KMEM
 	bool
-	depends on MEMCG && !SLOB
+	depends on MEMCG
 	default y
 
 config BLK_CGROUP

kernel/configs/tiny.config

@@ -7,6 +7,5 @@ CONFIG_KERNEL_XZ=y
 # CONFIG_KERNEL_LZO is not set
 # CONFIG_KERNEL_LZ4 is not set
 # CONFIG_SLAB is not set
-# CONFIG_SLOB_DEPRECATED is not set
 CONFIG_SLUB=y
 CONFIG_SLUB_TINY=y

mm/Kconfig

@@ -238,30 +238,8 @@ config SLUB
 	   and has enhanced diagnostics. SLUB is the default choice for
 	   a slab allocator.
 
-config SLOB_DEPRECATED
-	depends on EXPERT
-	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@kvack.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

mm/Kconfig.debug

@@ -60,9 +60,9 @@ config SLUB_DEBUG
 	select STACKDEPOT if STACKTRACE_SUPPORT
 	help
 	  SLUB has extensive debug support features. Disabling these can
-	  result in significant savings in code size. This also disables
-	  SLUB sysfs support. /sys/slab will not exist and there will be
-	  no support for cache validation etc.
+	  result in significant savings in code size. While /sys/kernel/slab
+	  will still exist (with SYSFS enabled), it will not provide e.g. cache
+	  validation.
 
 config SLUB_DEBUG_ON
 	bool "SLUB debugging on by default"