[RFC PATCH 00/15] kmem_cache instances with static storage duration

[RFC PATCH 00/15] kmem_cache instances with static storage duration

[Al Viro]

        kmem_cache_create() and friends create new instances of
struct kmem_cache and return pointers to those.  Quite a few things in
core kernel are allocated from such caches; each allocation involves
dereferencing an assign-once pointer and for sufficiently hot ones that
dereferencing does show in profiles.

        There had been patches floating around switching some of those
to runtime_const infrastructure.  Unfortunately, it's arch-specific
and most of the architectures lack it.

        There's an alternative approach applicable at least to the caches
that are never destroyed, which covers a lot of them.  No matter what,
runtime_const for pointers is not going to be faster than plain &,
so if we had struct kmem_cache instances with static storage duration, we
would be at least no worse off than we are with runtime_const variants.

        There are obstacles to doing that, but they turn out to be easy
to deal with.

1) as it is, struct kmem_cache is opaque for anything outside of a few
files in mm/*; that avoids serious headache with header dependencies,
etc., and it's not something we want to lose.  Solution: struct
kmem_cache_opaque, with the size and alignment identical to struct
kmem_cache.  Calculation of size and alignment can be done via the same
mechanism we use for asm-offsets.h and rq-offsets.h, with build-time
check for mismatches.  With that done, we get an opaque type defined in
linux/slab-static.h that can be used for declaring those caches.
In linux/slab.h we add a forward declaration of kmem_cache_opaque +
helper (to_kmem_cache()) converting a pointer to kmem_cache_opaque
into pointer to kmem_cache.

2) real constructor of kmem_cache needs to be taught to deal with
preallocated instances.  That turns out to be easy - we already pass an
obscene amount of optional arguments via struct kmem_cache_args, so we
can stash the pointer to preallocated instance in there.  Changes in
mm/slab_common.c are very minor - we should treat preallocated caches
as unmergable, use the instance passed to us instead of allocating a
new one and we should not free them.  That's it.

	A set of helpers parallel to kmem_cache_create() and friends
(kmem_cache_setup(), etc.) is provided in the same linux/slab-static.h;
generally, conversion affects only a few lines.

	Note that slab-static.h is needed only in places that create
such instances; all users need only slab.h (and they can be modular,
unlike runtime_const-based approach).


	That covers the instances that never get destroyed.  Quite a few
fall into that category, but there's a major exception - anything in
modules must be destroyed before the module gets removed.  Note that
unlike runtime_constant-based approach, cache _uses_ in a module are
fine - if kmem_cache_opaque instance is exported, its address is available
to modules without any problems.  It's caches _created_ in a module
that offer an extra twist.

	Teaching kmem_cache_destroy() to skip actual freeing of given
kmem_cache instance is trivial; the problem is that kmem_cache_destroy()
may overlap with sysfs access to attributes of that cache.  In that
case kmem_cache_destroy() may return before the instance gets freed -
freeing (from slab_kmem_cache_release()) happens when the refcount of
embedded kobject drops to zero.  That's fine, since all references
to data structures in module's memory are already gone by the time
kmem_cache_destroy() returns.  That, however, relies upon the struct
kmem_cache itself not being in module's memory; getting it unmapped
before slab_kmem_cache_release() has run needs to be avoided.

	It's not hard to deal with, though.  We need to make sure that
instance in a module will get to slab_kmem_cache_release() before the
module data gets freed.  That's only a problem on sysfs setups -
otherwise it'll definitely be finished before kmem_cache_destroy()
returns.

	Note that modules themselves have sysfs-exposed attributes,
so a similar problem already exists there.  That's dealt with by
having mod_sysfs_teardown() wait for refcount of module->mkobj.kobj
reaching zero.  Let's make use of that - have static-duration-in-module
kmem_cache instances grab a reference to that kobject upon setup and
drop it in the end of slab_kmem_cache_release().

	Let setup helpers store the kobjetct to be pinned in
kmem_cache_args->owner (for preallocated; if somebody manually sets it
for non-preallocated case, it'll be ignored).  That would be
&THIS_MODULE->mkobj.kobj for a module and NULL in built-in.

	If sysfs is enabled and we are dealing with preallocated instance,
let create_cache() grab and stash that reference in kmem_cache->owner
and let slab_kmem_cache_release() drop it instead of freeing kmem_cache
instance.


	Costs:
* a bit (SLAB_PREALLOCATED) is stolen from slab_flags_t
* such caches can't be merged.  If you want them mergable, don't use that
technics.
* you can't do kmem_cache_setup()/kmem_cache_destroy()/kmem_cache_setup()
on the same instance.  Just don't do that.

Al Viro (15):
  static kmem_cache instances for core caches
  allow static-duration kmem_cache in modules
  make mnt_cache static-duration
  turn thread_cache static-duration
  turn signal_cache static-duration
  turn bh_cachep static-duration
  turn dentry_cache static-duration
  turn files_cachep static-duration
  make filp and bfilp caches static-duration
  turn sighand_cache static-duration
  turn mm_cachep static-duration
  turn task_struct_cachep static-duration
  turn fs_cachep static-duration
  turn inode_cachep static-duration
  turn ufs_inode_cache static-duration

 Kbuild                            | 13 +++++-
 fs/buffer.c                       |  6 ++-
 fs/dcache.c                       |  8 ++--
 fs/file_table.c                   | 32 +++++++-------
 fs/inode.c                        |  6 ++-
 fs/namespace.c                    |  6 ++-
 fs/ufs/super.c                    |  9 ++--
 include/asm-generic/vmlinux.lds.h |  3 +-
 include/linux/fdtable.h           |  3 +-
 include/linux/fs_struct.h         |  3 +-
 include/linux/signal.h            |  3 +-
 include/linux/slab-static.h       | 69 +++++++++++++++++++++++++++++++
 include/linux/slab.h              | 11 +++++
 kernel/fork.c                     | 37 ++++++++++-------
 mm/kmem_cache_size.c              | 20 +++++++++
 mm/slab.h                         |  1 +
 mm/slab_common.c                  | 44 +++++++++++++-------
 mm/slub.c                         |  7 ++++
 18 files changed, 214 insertions(+), 67 deletions(-)
 create mode 100644 include/linux/slab-static.h
 create mode 100644 mm/kmem_cache_size.c

-- 
2.47.3

[RFC PATCH 01/15] static kmem_cache instances for core caches

[Al Viro]

        kmem_cache_create() and friends create new instances of
struct kmem_cache and return pointers to those.  Quite a few things in
core kernel are allocated from such caches; each allocation involves
dereferencing an assign-once pointer and for sufficiently hot ones that
dereferencing does show in profiles.

        There had been patches floating around switching some of those
to runtime_const infrastructure.  Unfortunately, it's arch-specific
and most of the architectures lack it.

        There's an alternative approach applicable at least to the caches
that are never destroyed, which covers a lot of them.  No matter what,
runtime_const for pointers is not going to be faster than plain &,
so if we had struct kmem_cache instances with static storage duration, we
would be at least no worse off than we are with runtime_const variants.

        There are obstacles to doing that, but they turn out to be easy
to deal with.

1) as it is, struct kmem_cache is opaque for anything outside of a few
files in mm/*; that avoids serious headache with header dependencies,
etc., and it's not something we want to lose.  Solution: struct
kmem_cache_opaque, with the size and alignment identical to struct
kmem_cache.  Calculation of size and alignment can be done via the same
mechanism we use for asm-offsets.h and rq-offsets.h, with build-time
check for mismatches.  With that done, we get an opaque type defined in
linux/slab-static.h that can be used for declaring those caches.
In linux/slab.h we add a forward declaration of kmem_cache_opaque +
helper (to_kmem_cache()) converting a pointer to kmem_cache_opaque
into pointer to kmem_cache.

2) real constructor of kmem_cache needs to be taught to deal with
preallocated instances.  That turns out to be easy - we already pass an
obscene amount of optional arguments via struct kmem_cache_args, so we
can stash the pointer to preallocated instance in there.  Changes in
mm/slab_common.c are very minor - we should treat preallocated caches
as unmergable, use the instance passed to us instead of allocating a
new one and we should not free them.  That's it.

	Note that slab-static.h is needed only in places that create
such instances; all users need only slab.h (and they can be modular,
unlike runtime_const-based approach).

	That covers the instances that never get destroyed.  Quite a few
fall into that category, but there's a major exception - anything in
modules must be destroyed before the module gets removed.  For example,
filesystems that have their inodes allocated from a private kmem_cache
can't make use of that technics for their inode allocations, etc.

	It's not that hard to deal with, but for now let's just ban
including slab-static.h from modules.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
 Kbuild                      | 13 +++++++-
 include/linux/slab-static.h | 65 +++++++++++++++++++++++++++++++++++++
 include/linux/slab.h        |  7 ++++
 mm/kmem_cache_size.c        | 20 ++++++++++++
 mm/slab_common.c            | 30 ++++++++---------
 mm/slub.c                   |  7 ++++
 6 files changed, 126 insertions(+), 16 deletions(-)
 create mode 100644 include/linux/slab-static.h
 create mode 100644 mm/kmem_cache_size.c

diff --git a/Kbuild b/Kbuild
index 13324b4bbe23..eb985a6614eb 100644
--- a/Kbuild
+++ b/Kbuild
@@ -45,13 +45,24 @@ kernel/sched/rq-offsets.s: $(offsets-file)
 $(rq-offsets-file): kernel/sched/rq-offsets.s FORCE
 	$(call filechk,offsets,__RQ_OFFSETS_H__)
 
+# generate kmem_cache_size.h
+
+kmem_cache_size-file := include/generated/kmem_cache_size.h
+
+targets += mm/kmem_cache_size.s
+
+mm/kmem_cache_size.s: $(rq-offsets-file)
+
+$(kmem_cache_size-file): mm/kmem_cache_size.s FORCE
+	$(call filechk,offsets,__KMEM_CACHE_SIZE_H__)
+
 # Check for missing system calls
 
 quiet_cmd_syscalls = CALL    $<
       cmd_syscalls = $(CONFIG_SHELL) $< $(CC) $(c_flags) $(missing_syscalls_flags)
 
 PHONY += missing-syscalls
-missing-syscalls: scripts/checksyscalls.sh $(rq-offsets-file)
+missing-syscalls: scripts/checksyscalls.sh $(kmem_cache_size-file)
 	$(call cmd,syscalls)
 
 # Check the manual modification of atomic headers
diff --git a/include/linux/slab-static.h b/include/linux/slab-static.h
new file mode 100644
index 000000000000..47b2220b4988
--- /dev/null
+++ b/include/linux/slab-static.h
@@ -0,0 +1,65 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_SLAB_STATIC_H
+#define _LINUX_SLAB_STATIC_H
+
+#ifdef MODULE
+#error "can't use that in modules"
+#endif
+
+#include <generated/kmem_cache_size.h>
+
+/* same size and alignment as struct kmem_cache: */
+struct kmem_cache_opaque {
+	unsigned char opaque[KMEM_CACHE_SIZE];
+} __aligned(KMEM_CACHE_ALIGN);
+
+#define __KMEM_CACHE_SETUP(cache, name, size, flags, ...)	\
+		__kmem_cache_create_args((name), (size),	\
+			&(struct kmem_cache_args) {		\
+				.preallocated = (cache),	\
+				__VA_ARGS__}, (flags))
+
+static inline int
+kmem_cache_setup_usercopy(struct kmem_cache *s,
+			  const char *name, unsigned int size,
+			  unsigned int align, slab_flags_t flags,
+			  unsigned int useroffset, unsigned int usersize,
+			  void (*ctor)(void *))
+{
+	struct kmem_cache *res;
+	res = __KMEM_CACHE_SETUP(s, name, size, flags,
+				.align		= align,
+				.ctor		= ctor,
+				.useroffset	= useroffset,
+				.usersize	= usersize);
+	if (IS_ERR(res))
+		return PTR_ERR(res);
+	return 0;
+}
+
+static inline int
+kmem_cache_setup(struct kmem_cache *s,
+		 const char *name, unsigned int size,
+		 unsigned int align, slab_flags_t flags,
+		 void (*ctor)(void *))
+{
+	struct kmem_cache *res;
+	res = __KMEM_CACHE_SETUP(s, name, size, flags,
+				.align		= align,
+				.ctor		= ctor);
+	if (IS_ERR(res))
+		return PTR_ERR(res);
+	return 0;
+}
+
+#define KMEM_CACHE_SETUP(s, __struct, __flags)                          	\
+	__KMEM_CACHE_SETUP((s), #__struct, sizeof(struct __struct), (__flags),	\
+			.align	= __alignof__(struct __struct))
+
+#define KMEM_CACHE_SETUP_USERCOPY(s, __struct, __flags, __field)		\
+	__KMEM_CACHE_SETUP((s), #__struct, sizeof(struct __struct), (__flags),	\
+			.align	= __alignof__(struct __struct),			\
+			.useroffset = offsetof(struct __struct, __field),	\
+			.usersize = sizeof_field(struct __struct, __field))
+
+#endif
diff --git a/include/linux/slab.h b/include/linux/slab.h
index 2482992248dc..f16c784148b4 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -261,11 +261,17 @@ enum _slab_flag_bits {
 
 struct list_lru;
 struct mem_cgroup;
+struct kmem_cache_opaque;
 /*
  * struct kmem_cache related prototypes
  */
 bool slab_is_available(void);
 
+static inline struct kmem_cache *to_kmem_cache(struct kmem_cache_opaque *p)
+{
+	return (struct kmem_cache *)p;
+}
+
 /**
  * struct kmem_cache_args - Less common arguments for kmem_cache_create()
  *
@@ -366,6 +372,7 @@ struct kmem_cache_args {
 	 * %0 means no sheaves will be created.
 	 */
 	unsigned int sheaf_capacity;
+	struct kmem_cache *preallocated;
 };
 
 struct kmem_cache *__kmem_cache_create_args(const char *name,
diff --git a/mm/kmem_cache_size.c b/mm/kmem_cache_size.c
new file mode 100644
index 000000000000..1ddbfa41a507
--- /dev/null
+++ b/mm/kmem_cache_size.c
@@ -0,0 +1,20 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Generate definitions needed by the preprocessor.
+ * This code generates raw asm output which is post-processed
+ * to extract and format the required data.
+ */
+
+#define COMPILE_OFFSETS
+#include <linux/kbuild.h>
+#include "slab.h"
+
+int main(void)
+{
+	/* The constants to put into include/generated/kmem_cache_size.h */
+	DEFINE(KMEM_CACHE_SIZE, sizeof(struct kmem_cache));
+	DEFINE(KMEM_CACHE_ALIGN, __alignof(struct kmem_cache));
+	/* End of constants */
+
+	return 0;
+}
diff --git a/mm/slab_common.c b/mm/slab_common.c
index eed7ea556cb1..81a413b44afb 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -224,33 +224,30 @@ static struct kmem_cache *create_cache(const char *name,
 				       struct kmem_cache_args *args,
 				       slab_flags_t flags)
 {
-	struct kmem_cache *s;
+	struct kmem_cache *s = args->preallocated;
 	int err;
 
 	/* If a custom freelist pointer is requested make sure it's sane. */
-	err = -EINVAL;
 	if (args->use_freeptr_offset &&
 	    (args->freeptr_offset >= object_size ||
 	     !(flags & SLAB_TYPESAFE_BY_RCU) ||
 	     !IS_ALIGNED(args->freeptr_offset, __alignof__(freeptr_t))))
-		goto out;
+		return ERR_PTR(-EINVAL);
 
-	err = -ENOMEM;
-	s = kmem_cache_zalloc(kmem_cache, GFP_KERNEL);
-	if (!s)
-		goto out;
+	if (!s) {
+		s = kmem_cache_zalloc(kmem_cache, GFP_KERNEL);
+		if (!s)
+			return ERR_PTR(-ENOMEM);
+	}
 	err = do_kmem_cache_create(s, name, object_size, args, flags);
-	if (err)
-		goto out_free_cache;
-
+	if (unlikely(err)) {
+		if (!args->preallocated)
+			kmem_cache_free(kmem_cache, s);
+		return ERR_PTR(err);
+	}
 	s->refcount = 1;
 	list_add(&s->list, &slab_caches);
 	return s;
-
-out_free_cache:
-	kmem_cache_free(kmem_cache, s);
-out:
-	return ERR_PTR(err);
 }
 
 /**
@@ -324,6 +321,9 @@ struct kmem_cache *__kmem_cache_create_args(const char *name,
 		    object_size - args->usersize < args->useroffset))
 		args->usersize = args->useroffset = 0;
 
+	if (args->preallocated)
+		flags |= SLAB_NO_MERGE;
+
 	if (!args->usersize && !args->sheaf_capacity)
 		s = __kmem_cache_alias(name, object_size, args->align, flags,
 				       args->ctor);
diff --git a/mm/slub.c b/mm/slub.c
index 861592ac5425..41fe79b3f055 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -47,6 +47,7 @@
 #include <linux/irq_work.h>
 #include <linux/kprobes.h>
 #include <linux/debugfs.h>
+#include <linux/slab-static.h>
 #include <trace/events/kmem.h>
 
 #include "internal.h"
@@ -8491,6 +8492,12 @@ void __init kmem_cache_init(void)
 		boot_kmem_cache_node;
 	int node;
 
+	/* verify that kmem_cache_opaque is correct */
+	BUILD_BUG_ON(sizeof(struct kmem_cache) !=
+		     sizeof(struct kmem_cache_opaque));
+	BUILD_BUG_ON(__alignof(struct kmem_cache) !=
+		     __alignof(struct kmem_cache_opaque));
+
 	if (debug_guardpage_minorder())
 		slub_max_order = 0;
 
-- 
2.47.3

[RFC PATCH 02/15] allow static-duration kmem_cache in modules

[Al Viro]

	We need to make sure that instance in a module will get to
slab_kmem_cache_release() before the module data gets freed.  That's only
a problem on sysfs setups - otherwise it'll definitely be finished before
kmem_cache_destroy() returns.

	Note that modules themselves have sysfs-exposed attributes,
so a similar problem already exists there.  That's dealt with by
having mod_sysfs_teardown() wait for refcount of module->mkobj.kobj
reaching zero.  Let's make use of that - have static-duration-in-module
kmem_cache instances grab a reference to that kobject upon setup and
drop it in the end of slab_kmem_cache_release().

	Let setup helpers store the kobjetct to be pinned in
kmem_cache_args->owner (for preallocated; if somebody manually sets it
for non-preallocated case, it'll be ignored).  That would be
&THIS_MODULE->mkobj.kobj for a module and NULL in built-in.

	If sysfs is enabled and we are dealing with preallocated instance,
let create_cache() grab and stash that reference in kmem_cache->owner
and let slab_kmem_cache_release() drop it instead of freeing kmem_cache
instance.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
 include/linux/slab-static.h | 12 ++++++++----
 include/linux/slab.h        |  4 ++++
 mm/slab.h                   |  1 +
 mm/slab_common.c            | 16 ++++++++++++++--
 4 files changed, 27 insertions(+), 6 deletions(-)

diff --git a/include/linux/slab-static.h b/include/linux/slab-static.h
index 47b2220b4988..16d1564b4a4b 100644
--- a/include/linux/slab-static.h
+++ b/include/linux/slab-static.h
@@ -2,10 +2,7 @@
 #ifndef _LINUX_SLAB_STATIC_H
 #define _LINUX_SLAB_STATIC_H
 
-#ifdef MODULE
-#error "can't use that in modules"
-#endif
-
+#include <linux/init.h>
 #include <generated/kmem_cache_size.h>
 
 /* same size and alignment as struct kmem_cache: */
@@ -13,9 +10,16 @@ struct kmem_cache_opaque {
 	unsigned char opaque[KMEM_CACHE_SIZE];
 } __aligned(KMEM_CACHE_ALIGN);
 
+#ifdef MODULE
+#define THIS_MODULE_KOBJ &THIS_MODULE->mkobj.kobj
+#else
+#define THIS_MODULE_KOBJ NULL
+#endif
+
 #define __KMEM_CACHE_SETUP(cache, name, size, flags, ...)	\
 		__kmem_cache_create_args((name), (size),	\
 			&(struct kmem_cache_args) {		\
+				.owner = THIS_MODULE_KOBJ,	\
 				.preallocated = (cache),	\
 				__VA_ARGS__}, (flags))
 
diff --git a/include/linux/slab.h b/include/linux/slab.h
index f16c784148b4..dc1aeb14a12b 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -60,6 +60,7 @@ enum _slab_flag_bits {
 #ifdef CONFIG_SLAB_OBJ_EXT
 	_SLAB_NO_OBJ_EXT,
 #endif
+	_SLAB_PREALLOCATED,
 	_SLAB_FLAGS_LAST_BIT
 };
 
@@ -244,6 +245,8 @@ enum _slab_flag_bits {
 #define SLAB_NO_OBJ_EXT		__SLAB_FLAG_UNUSED
 #endif
 
+#define SLAB_PREALLOCATED	__SLAB_FLAG_BIT(_SLAB_PREALLOCATED)
+
 /*
  * ZERO_SIZE_PTR will be returned for zero sized kmalloc requests.
  *
@@ -373,6 +376,7 @@ struct kmem_cache_args {
 	 */
 	unsigned int sheaf_capacity;
 	struct kmem_cache *preallocated;
+	struct kobject *owner;
 };
 
 struct kmem_cache *__kmem_cache_create_args(const char *name,
diff --git a/mm/slab.h b/mm/slab.h
index e767aa7e91b0..9ff9a0a3b164 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -249,6 +249,7 @@ struct kmem_cache {
 	struct list_head list;		/* List of slab caches */
 #ifdef CONFIG_SYSFS
 	struct kobject kobj;		/* For sysfs */
+	struct kobject *owner;		/* keep that pinned while alive */
 #endif
 #ifdef CONFIG_SLAB_FREELIST_HARDENED
 	unsigned long random;
diff --git a/mm/slab_common.c b/mm/slab_common.c
index 81a413b44afb..a854e6872acd 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -245,6 +245,12 @@ static struct kmem_cache *create_cache(const char *name,
 			kmem_cache_free(kmem_cache, s);
 		return ERR_PTR(err);
 	}
+#ifdef CONFIG_SYSFS
+	if (flags & SLAB_PREALLOCATED) {
+		s->owner = args->owner;
+		kobject_get(s->owner);
+	}
+#endif
 	s->refcount = 1;
 	list_add(&s->list, &slab_caches);
 	return s;
@@ -322,7 +328,7 @@ struct kmem_cache *__kmem_cache_create_args(const char *name,
 		args->usersize = args->useroffset = 0;
 
 	if (args->preallocated)
-		flags |= SLAB_NO_MERGE;
+		flags |= SLAB_NO_MERGE | SLAB_PREALLOCATED;
 
 	if (!args->usersize && !args->sheaf_capacity)
 		s = __kmem_cache_alias(name, object_size, args->align, flags,
@@ -481,7 +487,13 @@ void slab_kmem_cache_release(struct kmem_cache *s)
 {
 	__kmem_cache_release(s);
 	kfree_const(s->name);
-	kmem_cache_free(kmem_cache, s);
+	if (!(s->flags & SLAB_PREALLOCATED)) {
+		kmem_cache_free(kmem_cache, s);
+		return;
+	}
+#ifdef CONFIG_SYSFS
+	kobject_put(s->owner);
+#endif
 }
 
 void kmem_cache_destroy(struct kmem_cache *s)
-- 
2.47.3

[RFC PATCH 03/15] make mnt_cache static-duration

[Al Viro]

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
 fs/namespace.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/namespace.c b/fs/namespace.c
index c58674a20cad..9a9882df463d 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -34,6 +34,7 @@
 #include <linux/mnt_idmapping.h>
 #include <linux/pidfs.h>
 #include <linux/nstree.h>
+#include <linux/slab-static.h>
 
 #include "pnode.h"
 #include "internal.h"
@@ -85,7 +86,8 @@ static u64 mnt_id_ctr = MNT_UNIQUE_ID_OFFSET;
 
 static struct hlist_head *mount_hashtable __ro_after_init;
 static struct hlist_head *mountpoint_hashtable __ro_after_init;
-static struct kmem_cache *mnt_cache __ro_after_init;
+static struct kmem_cache_opaque __mnt_cache;
+#define mnt_cache to_kmem_cache(&__mnt_cache)
 static DECLARE_RWSEM(namespace_sem);
 static HLIST_HEAD(unmounted);	/* protected by namespace_sem */
 static LIST_HEAD(ex_mountpoints); /* protected by namespace_sem */
@@ -5997,7 +5999,7 @@ void __init mnt_init(void)
 {
 	int err;
 
-	mnt_cache = kmem_cache_create("mnt_cache", sizeof(struct mount),
+	kmem_cache_setup(mnt_cache, "mnt_cache", sizeof(struct mount),
 			0, SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT, NULL);
 
 	mount_hashtable = alloc_large_system_hash("Mount-cache",
-- 
2.47.3

[RFC PATCH 04/15] turn thread_cache static-duration

[Al Viro]

... and make is SLAB_PANIC instead of simulating it with BUG_ON() -
the boot is not going to get to kernel threads, nevermind userland...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
 kernel/fork.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/kernel/fork.c b/kernel/fork.c
index b1f3915d5f8e..ddd2558f9431 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -108,6 +108,7 @@
 #include <linux/unwind_deferred.h>
 #include <linux/pgalloc.h>
 #include <linux/uaccess.h>
+#include <linux/slab-static.h>
 
 #include <asm/mmu_context.h>
 #include <asm/cacheflush.h>
@@ -422,7 +423,8 @@ static void free_thread_stack(struct task_struct *tsk)
 
 #else /* !(THREAD_SIZE >= PAGE_SIZE) */
 
-static struct kmem_cache *thread_stack_cache;
+static struct kmem_cache_opaque __thread_stack_cache;
+#define thread_stack_cache to_kmem_cache(&__thread_stack_cache)
 
 static void thread_stack_free_rcu(struct rcu_head *rh)
 {
@@ -453,10 +455,10 @@ static void free_thread_stack(struct task_struct *tsk)
 
 void thread_stack_cache_init(void)
 {
-	thread_stack_cache = kmem_cache_create_usercopy("thread_stack",
-					THREAD_SIZE, THREAD_SIZE, 0, 0,
+	kmem_cache_setup_usercopy(thread_stack_cache, "thread_stack",
+					THREAD_SIZE, THREAD_SIZE,
+					SLAB_PANIC, 0,
 					THREAD_SIZE, NULL);
-	BUG_ON(thread_stack_cache == NULL);
 }
 
 #endif /* THREAD_SIZE >= PAGE_SIZE */
-- 
2.47.3

[RFC PATCH 05/15] turn signal_cache static-duration

[Al Viro]

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
 kernel/fork.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/fork.c b/kernel/fork.c
index ddd2558f9431..23ed80d0d6d0 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -465,7 +465,8 @@ void thread_stack_cache_init(void)
 #endif /* CONFIG_VMAP_STACK */
 
 /* SLAB cache for signal_struct structures (tsk->signal) */
-static struct kmem_cache *signal_cachep;
+static struct kmem_cache_opaque signal_cache;
+#define signal_cachep to_kmem_cache(&signal_cache)
 
 /* SLAB cache for sighand_struct structures (tsk->sighand) */
 struct kmem_cache *sighand_cachep;
@@ -3024,7 +3025,7 @@ void __init proc_caches_init(void)
 			sizeof(struct sighand_struct), 0,
 			SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_TYPESAFE_BY_RCU|
 			SLAB_ACCOUNT, sighand_ctor);
-	signal_cachep = kmem_cache_create("signal_cache",
+	kmem_cache_setup(signal_cachep, "signal_cache",
 			sizeof(struct signal_struct), 0,
 			SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT,
 			NULL);
-- 
2.47.3

[RFC PATCH 06/15] turn bh_cachep static-duration

[Al Viro]

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
 fs/buffer.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/buffer.c b/fs/buffer.c
index 838c0c571022..c8ec1b440880 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -50,6 +50,7 @@
 #include <linux/fscrypt.h>
 #include <linux/fsverity.h>
 #include <linux/sched/isolation.h>
+#include <linux/slab-static.h>
 
 #include "internal.h"
 
@@ -2990,7 +2991,8 @@ EXPORT_SYMBOL(try_to_free_buffers);
 /*
  * Buffer-head allocation
  */
-static struct kmem_cache *bh_cachep __ro_after_init;
+static struct kmem_cache_opaque bh_cache;
+#define bh_cachep to_kmem_cache(&bh_cache)
 
 /*
  * Once the number of bh's in the machine exceeds this level, we start
@@ -3149,7 +3151,7 @@ void __init buffer_init(void)
 	unsigned long nrpages;
 	int ret;
 
-	bh_cachep = KMEM_CACHE(buffer_head,
+	KMEM_CACHE_SETUP(bh_cachep, buffer_head,
 				SLAB_RECLAIM_ACCOUNT|SLAB_PANIC);
 	/*
 	 * Limit the bh occupancy to 10% of ZONE_NORMAL
-- 
2.47.3

[RFC PATCH 07/15] turn dentry_cache static-duration

[Al Viro]

No need to bother with runtime_const() for it anymore...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
 fs/dcache.c                       | 8 ++++----
 include/asm-generic/vmlinux.lds.h | 3 +--
 2 files changed, 5 insertions(+), 6 deletions(-)

diff --git a/fs/dcache.c b/fs/dcache.c
index dc2fff4811d1..43d3b4fbedcc 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -32,6 +32,7 @@
 #include <linux/bit_spinlock.h>
 #include <linux/rculist_bl.h>
 #include <linux/list_lru.h>
+#include <linux/slab-static.h>
 #include "internal.h"
 #include "mount.h"
 
@@ -86,8 +87,8 @@ __cacheline_aligned_in_smp DEFINE_SEQLOCK(rename_lock);
 
 EXPORT_SYMBOL(rename_lock);
 
-static struct kmem_cache *__dentry_cache __ro_after_init;
-#define dentry_cache runtime_const_ptr(__dentry_cache)
+static struct kmem_cache_opaque __dentry_cache;
+#define dentry_cache to_kmem_cache(&__dentry_cache)
 
 const struct qstr empty_name = QSTR_INIT("", 0);
 EXPORT_SYMBOL(empty_name);
@@ -3265,10 +3266,9 @@ static void __init dcache_init(void)
 	 * but it is probably not worth it because of the cache nature
 	 * of the dcache.
 	 */
-	__dentry_cache = KMEM_CACHE_USERCOPY(dentry,
+	KMEM_CACHE_SETUP_USERCOPY(dentry_cache, dentry,
 		SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|SLAB_ACCOUNT,
 		d_shortname.string);
-	runtime_const_init(ptr, __dentry_cache);
 
 	/* Hash may have been set up in dcache_init_early */
 	if (!hashdist)
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 8ca130af301f..6997f6301260 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -971,8 +971,7 @@
 
 #define RUNTIME_CONST_VARIABLES						\
 		RUNTIME_CONST(shift, d_hash_shift)			\
-		RUNTIME_CONST(ptr, dentry_hashtable)			\
-		RUNTIME_CONST(ptr, __dentry_cache)
+		RUNTIME_CONST(ptr, dentry_hashtable)
 
 /* Alignment must be consistent with (kunit_suite *) in include/kunit/test.h */
 #define KUNIT_TABLE()							\
-- 
2.47.3

[RFC PATCH 08/15] turn files_cachep static-duration

[Al Viro]

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
 include/linux/fdtable.h | 3 ++-
 kernel/fork.c           | 4 ++--
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/include/linux/fdtable.h b/include/linux/fdtable.h
index c45306a9f007..f2d553f99c58 100644
--- a/include/linux/fdtable.h
+++ b/include/linux/fdtable.h
@@ -113,6 +113,7 @@ int iterate_fd(struct files_struct *, unsigned,
 extern int close_fd(unsigned int fd);
 extern struct file *file_close_fd(unsigned int fd);
 
-extern struct kmem_cache *files_cachep;
+extern struct kmem_cache_opaque files_cache;
+#define files_cachep to_kmem_cache(&files_cache)
 
 #endif /* __LINUX_FDTABLE_H */
diff --git a/kernel/fork.c b/kernel/fork.c
index 23ed80d0d6d0..8c4d9a81ef42 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -472,7 +472,7 @@ static struct kmem_cache_opaque signal_cache;
 struct kmem_cache *sighand_cachep;
 
 /* SLAB cache for files_struct structures (tsk->files) */
-struct kmem_cache *files_cachep;
+struct kmem_cache_opaque files_cache;
 
 /* SLAB cache for fs_struct structures (tsk->fs) */
 struct kmem_cache *fs_cachep;
@@ -3029,7 +3029,7 @@ void __init proc_caches_init(void)
 			sizeof(struct signal_struct), 0,
 			SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT,
 			NULL);
-	files_cachep = kmem_cache_create("files_cache",
+	kmem_cache_setup(files_cachep, "files_cache",
 			sizeof(struct files_struct), 0,
 			SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT,
 			NULL);
-- 
2.47.3

[RFC PATCH 09/15] make filp and bfilp caches static-duration

[Al Viro]

As much as I hate it, the name "filp" is a part of userland ABI at this
point - scripts grepping for it in /proc/slabinfo do exist ;-/

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
 fs/file_table.c | 32 ++++++++++++++++++--------------
 1 file changed, 18 insertions(+), 14 deletions(-)

diff --git a/fs/file_table.c b/fs/file_table.c
index cd4a3db4659a..18a992b40109 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -27,6 +27,7 @@
 #include <linux/task_work.h>
 #include <linux/swap.h>
 #include <linux/kmemleak.h>
+#include <linux/slab-static.h>
 
 #include <linux/atomic.h>
 
@@ -38,8 +39,10 @@ static struct files_stat_struct files_stat = {
 };
 
 /* SLAB cache for file structures */
-static struct kmem_cache *filp_cachep __ro_after_init;
-static struct kmem_cache *bfilp_cachep __ro_after_init;
+static struct kmem_cache_opaque file_cache;
+static struct kmem_cache_opaque backing_file_cache;
+#define filp_cachep to_kmem_cache(&file_cache)
+#define bfilp_cachep to_kmem_cache(&backing_file_cache)
 
 static struct percpu_counter nr_files __cacheline_aligned_in_smp;
 
@@ -587,19 +590,20 @@ void fput_close(struct file *file)
 
 void __init files_init(void)
 {
-	struct kmem_cache_args args = {
-		.use_freeptr_offset = true,
-		.freeptr_offset = offsetof(struct file, f_freeptr),
-	};
-
-	filp_cachep = kmem_cache_create("filp", sizeof(struct file), &args,
-				SLAB_HWCACHE_ALIGN | SLAB_PANIC |
-				SLAB_ACCOUNT | SLAB_TYPESAFE_BY_RCU);
+	__KMEM_CACHE_SETUP(filp_cachep, "filp", sizeof(struct file),
+			   SLAB_HWCACHE_ALIGN | SLAB_PANIC |
+			   SLAB_ACCOUNT | SLAB_TYPESAFE_BY_RCU,
+			   .use_freeptr_offset = true,
+			   .freeptr_offset = offsetof(struct file,
+						      f_freeptr));
+
+	__KMEM_CACHE_SETUP(bfilp_cachep, "bfilp", sizeof(struct backing_file),
+			   SLAB_HWCACHE_ALIGN | SLAB_PANIC |
+			   SLAB_ACCOUNT | SLAB_TYPESAFE_BY_RCU,
+			   .use_freeptr_offset = true,
+			   .freeptr_offset = offsetof(struct backing_file,
+						      bf_freeptr));
 
-	args.freeptr_offset = offsetof(struct backing_file, bf_freeptr);
-	bfilp_cachep = kmem_cache_create("bfilp", sizeof(struct backing_file),
-				&args, SLAB_HWCACHE_ALIGN | SLAB_PANIC |
-				SLAB_ACCOUNT | SLAB_TYPESAFE_BY_RCU);
 	percpu_counter_init(&nr_files, 0, GFP_KERNEL);
 }
 
-- 
2.47.3

[RFC PATCH 10/15] turn sighand_cache static-duration

[Al Viro]

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
 include/linux/signal.h | 3 ++-
 kernel/fork.c          | 4 ++--
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/include/linux/signal.h b/include/linux/signal.h
index f19816832f05..a0c7fee8b22a 100644
--- a/include/linux/signal.h
+++ b/include/linux/signal.h
@@ -323,7 +323,8 @@ static inline void disallow_signal(int sig)
 	kernel_sigaction(sig, SIG_IGN);
 }
 
-extern struct kmem_cache *sighand_cachep;
+extern struct kmem_cache_opaque sighand_cache;
+#define sighand_cachep to_kmem_cache(&sighand_cache)
 
 extern bool unhandled_signal(struct task_struct *tsk, int sig);
 
diff --git a/kernel/fork.c b/kernel/fork.c
index 8c4d9a81ef42..d5b7e4d51596 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -469,7 +469,7 @@ static struct kmem_cache_opaque signal_cache;
 #define signal_cachep to_kmem_cache(&signal_cache)
 
 /* SLAB cache for sighand_struct structures (tsk->sighand) */
-struct kmem_cache *sighand_cachep;
+struct kmem_cache_opaque sighand_cache;
 
 /* SLAB cache for files_struct structures (tsk->files) */
 struct kmem_cache_opaque files_cache;
@@ -3021,7 +3021,7 @@ void __init mm_cache_init(void)
 
 void __init proc_caches_init(void)
 {
-	sighand_cachep = kmem_cache_create("sighand_cache",
+	kmem_cache_setup(sighand_cachep, "sighand_cache",
 			sizeof(struct sighand_struct), 0,
 			SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_TYPESAFE_BY_RCU|
 			SLAB_ACCOUNT, sighand_ctor);
-- 
2.47.3

[RFC PATCH 11/15] turn mm_cachep static-duration

[Al Viro]

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
 kernel/fork.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/fork.c b/kernel/fork.c
index d5b7e4d51596..f83ca2f5826f 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -478,7 +478,8 @@ struct kmem_cache_opaque files_cache;
 struct kmem_cache *fs_cachep;
 
 /* SLAB cache for mm_struct structures (tsk->mm) */
-static struct kmem_cache *mm_cachep;
+static struct kmem_cache_opaque mm_cache;
+#define mm_cachep to_kmem_cache(&mm_cache)
 
 static void account_kernel_stack(struct task_struct *tsk, int account)
 {
@@ -3011,7 +3012,7 @@ void __init mm_cache_init(void)
 	 */
 	mm_size = sizeof(struct mm_struct) + cpumask_size() + mm_cid_size();
 
-	mm_cachep = kmem_cache_create_usercopy("mm_struct",
+	kmem_cache_setup_usercopy(mm_cachep, "mm_struct",
 			mm_size, ARCH_MIN_MMSTRUCT_ALIGN,
 			SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT,
 			offsetof(struct mm_struct, saved_auxv),
-- 
2.47.3

[RFC PATCH 12/15] turn task_struct_cachep static-duration

[Al Viro]

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
 kernel/fork.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/fork.c b/kernel/fork.c
index f83ca2f5826f..8f0dfefd82f0 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -178,7 +178,8 @@ void __weak arch_release_task_struct(struct task_struct *tsk)
 {
 }
 
-static struct kmem_cache *task_struct_cachep;
+static struct kmem_cache_opaque task_struct_cache;
+#define task_struct_cachep to_kmem_cache(&task_struct_cache)
 
 static inline struct task_struct *alloc_task_struct_node(int node)
 {
@@ -860,7 +861,7 @@ void __init fork_init(void)
 
 	/* create a slab on which task_structs can be allocated */
 	task_struct_whitelist(&useroffset, &usersize);
-	task_struct_cachep = kmem_cache_create_usercopy("task_struct",
+	kmem_cache_setup_usercopy(task_struct_cachep, "task_struct",
 			arch_task_struct_size, align,
 			SLAB_PANIC|SLAB_ACCOUNT,
 			useroffset, usersize, NULL);
-- 
2.47.3

[RFC PATCH 13/15] turn fs_cachep static-duration

[Al Viro]

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
 include/linux/fs_struct.h | 3 ++-
 kernel/fork.c             | 4 ++--
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/include/linux/fs_struct.h b/include/linux/fs_struct.h
index 0070764b790a..e8c9fac5b7b7 100644
--- a/include/linux/fs_struct.h
+++ b/include/linux/fs_struct.h
@@ -15,7 +15,8 @@ struct fs_struct {
 	struct path root, pwd;
 } __randomize_layout;
 
-extern struct kmem_cache *fs_cachep;
+extern struct kmem_cache_opaque fs_struct_cache;
+#define fs_cachep to_kmem_cache(&fs_struct_cache)
 
 extern void exit_fs(struct task_struct *);
 extern void set_fs_root(struct fs_struct *, const struct path *);
diff --git a/kernel/fork.c b/kernel/fork.c
index 8f0dfefd82f0..7262abd0d2a4 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -476,7 +476,7 @@ struct kmem_cache_opaque sighand_cache;
 struct kmem_cache_opaque files_cache;
 
 /* SLAB cache for fs_struct structures (tsk->fs) */
-struct kmem_cache *fs_cachep;
+struct kmem_cache_opaque fs_struct_cache;
 
 /* SLAB cache for mm_struct structures (tsk->mm) */
 static struct kmem_cache_opaque mm_cache;
@@ -3035,7 +3035,7 @@ void __init proc_caches_init(void)
 			sizeof(struct files_struct), 0,
 			SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT,
 			NULL);
-	fs_cachep = kmem_cache_create("fs_cache",
+	kmem_cache_setup(fs_cachep, "fs_cache",
 			sizeof(struct fs_struct), 0,
 			SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT,
 			NULL);
-- 
2.47.3

[RFC PATCH 14/15] turn inode_cachep static-duration

[Al Viro]

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
 fs/inode.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/inode.c b/fs/inode.c
index 521383223d8a..7c212696ba67 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -23,6 +23,7 @@
 #include <linux/rw_hint.h>
 #include <linux/seq_file.h>
 #include <linux/debugfs.h>
+#include <linux/slab-static.h>
 #include <trace/events/writeback.h>
 #define CREATE_TRACE_POINTS
 #include <trace/events/timestamp.h>
@@ -76,7 +77,8 @@ EXPORT_SYMBOL(empty_aops);
 static DEFINE_PER_CPU(unsigned long, nr_inodes);
 static DEFINE_PER_CPU(unsigned long, nr_unused);
 
-static struct kmem_cache *inode_cachep __ro_after_init;
+static struct kmem_cache_opaque inode_cache;
+#define inode_cachep to_kmem_cache(&inode_cache)
 
 static long get_nr_inodes(void)
 {
@@ -2564,7 +2566,7 @@ void __init inode_init_early(void)
 void __init inode_init(void)
 {
 	/* inode slab cache */
-	inode_cachep = kmem_cache_create("inode_cache",
+	kmem_cache_setup(inode_cachep, "inode_cache",
 					 sizeof(struct inode),
 					 0,
 					 (SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|
-- 
2.47.3

[RFC PATCH 15/15] turn ufs_inode_cache static-duration

[Al Viro]

A modular example I used for testing...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
 fs/ufs/super.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/fs/ufs/super.c b/fs/ufs/super.c
index 6e4585169f94..440229a5b6c9 100644
--- a/fs/ufs/super.c
+++ b/fs/ufs/super.c
@@ -90,6 +90,7 @@
 #include <linux/log2.h>
 #include <linux/seq_file.h>
 #include <linux/iversion.h>
+#include <linux/slab-static.h>
 
 #include "ufs_fs.h"
 #include "ufs.h"
@@ -1354,7 +1355,8 @@ static int ufs_statfs(struct dentry *dentry, struct kstatfs *buf)
 	return 0;
 }
 
-static struct kmem_cache * ufs_inode_cachep;
+static struct kmem_cache_opaque ufs_inode_cache;
+#define ufs_inode_cachep to_kmem_cache(&ufs_inode_cache)
 
 static struct inode *ufs_alloc_inode(struct super_block *sb)
 {
@@ -1384,16 +1386,13 @@ static void init_once(void *foo)
 
 static int __init init_inodecache(void)
 {
-	ufs_inode_cachep = kmem_cache_create_usercopy("ufs_inode_cache",
+	return kmem_cache_setup_usercopy(ufs_inode_cachep, "ufs_inode_cache",
 				sizeof(struct ufs_inode_info), 0,
 				(SLAB_RECLAIM_ACCOUNT | SLAB_ACCOUNT),
 				offsetof(struct ufs_inode_info, i_u1.i_symlink),
 				sizeof_field(struct ufs_inode_info,
 					i_u1.i_symlink),
 				init_once);
-	if (ufs_inode_cachep == NULL)
-		return -ENOMEM;
-	return 0;
 }
 
 static void destroy_inodecache(void)
-- 
2.47.3

Re: [RFC PATCH 00/15] kmem_cache instances with static storage duration

[Linus Torvalds]

On Fri, 9 Jan 2026 at 18:01, Al Viro <viro@zeniv.linux.org.uk> wrote:
>
>         There's an alternative approach applicable at least to the caches
> that are never destroyed, which covers a lot of them.  No matter what,
> runtime_const for pointers is not going to be faster than plain &,
> so if we had struct kmem_cache instances with static storage duration, we
> would be at least no worse off than we are with runtime_const variants.

I like it. Much better than runtime_const for these things.

That said, I don't love the commit messages. "turn xyzzy
static-duration" reads very oddly to me, and because I saw the emails
out of order originally it just made me go "whaa?"

So can we please explain this some more obvious way. Maybe just "Make
xyz be statically allocated". Yes, I'm nitpicking, but I feel like
explaining core patches is worth the effort.

And maybe that's for the sad reason that I read more explanations than
code these days '/

                Linus

Re: [RFC PATCH 01/15] static kmem_cache instances for core caches

[Matthew Wilcox]

On Sat, Jan 10, 2026 at 04:02:03AM +0000, Al Viro wrote:
> +++ b/Kbuild
> @@ -45,13 +45,24 @@ kernel/sched/rq-offsets.s: $(offsets-file)
>  $(rq-offsets-file): kernel/sched/rq-offsets.s FORCE
>  	$(call filechk,offsets,__RQ_OFFSETS_H__)
>  
> +# generate kmem_cache_size.h
> +
> +kmem_cache_size-file := include/generated/kmem_cache_size.h
> +
> +targets += mm/kmem_cache_size.s
> +
> +mm/kmem_cache_size.s: $(rq-offsets-file)
> +
> +$(kmem_cache_size-file): mm/kmem_cache_size.s FORCE
> +	$(call filechk,offsets,__KMEM_CACHE_SIZE_H__)
> +
>  # Check for missing system calls
>  
>  quiet_cmd_syscalls = CALL    $<
>        cmd_syscalls = $(CONFIG_SHELL) $< $(CC) $(c_flags) $(missing_syscalls_flags)
>  
>  PHONY += missing-syscalls
> -missing-syscalls: scripts/checksyscalls.sh $(rq-offsets-file)
> +missing-syscalls: scripts/checksyscalls.sh $(kmem_cache_size-file)
>  	$(call cmd,syscalls)

Did you mean to _replace_  rq-offsets-file rather than add
kmem_cache_size-file ?

(I also wonder if we want to just do slab or if we want to make this
mm-offsets.h and maybe put other things in it later, but I'm having
trouble thinking of other things we might want to generate)

Re: [RFC PATCH 00/15] kmem_cache instances with static storage duration

[Al Viro]

On Fri, Jan 09, 2026 at 07:33:41PM -1000, Linus Torvalds wrote:
> On Fri, 9 Jan 2026 at 18:01, Al Viro <viro@zeniv.linux.org.uk> wrote:
> >
> >         There's an alternative approach applicable at least to the caches
> > that are never destroyed, which covers a lot of them.  No matter what,
> > runtime_const for pointers is not going to be faster than plain &,
> > so if we had struct kmem_cache instances with static storage duration, we
> > would be at least no worse off than we are with runtime_const variants.
> 
> I like it. Much better than runtime_const for these things.
> 
> That said, I don't love the commit messages. "turn xyzzy
> static-duration" reads very oddly to me, and because I saw the emails
> out of order originally it just made me go "whaa?"
> 
> So can we please explain this some more obvious way. Maybe just "Make
> xyz be statically allocated". Yes, I'm nitpicking, but I feel like
> explaining core patches is worth the effort.

Point, but TBH the tail of the series is basically a demo for conversions
as well as "this is what I'd been testing, FSVO".  In non-RFC form these
would be folded into fewer commits, if nothing else...

I'd really like to hear comments on the first two commits from SLAB
maintainers - for example, if slab_flags_t bits are considered a scarce
resource, the second commit would need to be modified.  Still doable, but
representation would be more convoluted...

Another question is whether it's worth checking for accidental call
of e.g. kmem_cache_setup() on an already initialized cache, statically
or dynamically allocated.  Again, up to maintainers - their subsystem,
their preferences.

Re: [RFC PATCH 01/15] static kmem_cache instances for core caches

[Al Viro]

On Sat, Jan 10, 2026 at 05:40:34AM +0000, Matthew Wilcox wrote:
> On Sat, Jan 10, 2026 at 04:02:03AM +0000, Al Viro wrote:
> > +++ b/Kbuild
> > @@ -45,13 +45,24 @@ kernel/sched/rq-offsets.s: $(offsets-file)
> >  $(rq-offsets-file): kernel/sched/rq-offsets.s FORCE
> >  	$(call filechk,offsets,__RQ_OFFSETS_H__)
> >  
> > +# generate kmem_cache_size.h
> > +
> > +kmem_cache_size-file := include/generated/kmem_cache_size.h
> > +
> > +targets += mm/kmem_cache_size.s
> > +
> > +mm/kmem_cache_size.s: $(rq-offsets-file)
> > +
> > +$(kmem_cache_size-file): mm/kmem_cache_size.s FORCE
> > +	$(call filechk,offsets,__KMEM_CACHE_SIZE_H__)
> > +
> >  # Check for missing system calls
> >  
> >  quiet_cmd_syscalls = CALL    $<
> >        cmd_syscalls = $(CONFIG_SHELL) $< $(CC) $(c_flags) $(missing_syscalls_flags)
> >  
> >  PHONY += missing-syscalls
> > -missing-syscalls: scripts/checksyscalls.sh $(rq-offsets-file)
> > +missing-syscalls: scripts/checksyscalls.sh $(kmem_cache_size-file)
> >  	$(call cmd,syscalls)
> 
> Did you mean to _replace_  rq-offsets-file rather than add
> kmem_cache_size-file ?

Insert kmem_cache_size-file into the chain, actually.  At the moment, mainline has
$(bounds-file): kernel/bounds.s FORCE
        $(call filechk,offsets,__LINUX_BOUNDS_H__)

$(timeconst-file): kernel/time/timeconst.bc FORCE
        $(call filechk,gentimeconst)

arch/$(SRCARCH)/kernel/asm-offsets.s: $(timeconst-file) $(bounds-file)

$(offsets-file): arch/$(SRCARCH)/kernel/asm-offsets.s FORCE
        $(call filechk,offsets,__ASM_OFFSETS_H__)

kernel/sched/rq-offsets.s: $(offsets-file)

$(rq-offsets-file): kernel/sched/rq-offsets.s FORCE
        $(call filechk,offsets,__RQ_OFFSETS_H__)

missing-syscalls: scripts/checksyscalls.sh $(rq-offsets-file)
        $(call cmd,syscalls)

with prepare having deps on $(offsets-file) and missing-syscalls, which
orders the entire sequence.