Message-ID: <b2c9cbf5-c39e-4a38-aa50-7e37145176ab@lucifer.local>
Date: Mon, 28 Apr 2025 21:29:18 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: "Liam R . Howlett" <Liam.Howlett@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>, Jann Horn <jannh@...gle.com>,
        Pedro Falcato <pfalcato@...e.de>, David Hildenbrand <david@...hat.com>,
        Kees Cook <kees@...nel.org>, Alexander Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
        Suren Baghdasaryan <surenb@...gle.com>, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 4/4] mm: perform VMA allocation, freeing, duplication
 in mm

Andrew - I maanged to typo vma_init.c to vma_init.h here in mm/vma.c (at least I
was consistent in these silly typos...).

Would you prefer a fixpatch or is it ok for you to quickly fix that up?

Thanks!

On Mon, Apr 28, 2025 at 04:28:17PM +0100, Lorenzo Stoakes wrote:
> Right now these are performed in kernel/fork.c which is odd and a violation
> of separation of concerns, as well as preventing us from integrating this
> and related logic into userland VMA testing going forward, and perhaps more
> importantly - enabling us to, in a subsequent commit, make VMA
> allocation/freeing a purely internal mm operation.
>
> There is a fly in the ointment - nommu - mmap.c is not compiled if
> CONFIG_MMU not set, and neither is vma.c.
>
> To square the circle, let's add a new file - vma_init.c. This will be
> compiled for both CONFIG_MMU and nommu builds, and will also form part of
> the VMA userland testing.
>
> This allows us to de-duplicate code, while maintaining separation of
> concerns and the ability for us to userland test this logic.
>
> Update the VMA userland tests accordingly, additionally adding a
> detach_free_vma() helper function to correctly detach VMAs before freeing
> them in test code, as this change was triggering the assert for this.
>
> Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
> ---
>  MAINTAINERS                      |   1 +
>  kernel/fork.c                    |  88 -------------------
>  mm/Makefile                      |   2 +-
>  mm/mmap.c                        |   3 +-
>  mm/nommu.c                       |   4 +-
>  mm/vma.h                         |   7 ++
>  mm/vma_init.c                    | 101 ++++++++++++++++++++++
>  tools/testing/vma/Makefile       |   2 +-
>  tools/testing/vma/vma.c          |  26 ++++--
>  tools/testing/vma/vma_internal.h | 143 +++++++++++++++++++++++++------
>  10 files changed, 251 insertions(+), 126 deletions(-)
>  create mode 100644 mm/vma_init.c
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 1ee1c22e6e36..d274e6802ba5 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -15656,6 +15656,7 @@ F:	mm/mseal.c
>  F:	mm/vma.c
>  F:	mm/vma.h
>  F:	mm/vma_exec.c
> +F:	mm/vma_init.c
>  F:	mm/vma_internal.h
>  F:	tools/testing/selftests/mm/merge.c
>  F:	tools/testing/vma/
> diff --git a/kernel/fork.c b/kernel/fork.c
> index ac9f9267a473..9e4616dacd82 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -431,88 +431,9 @@ struct kmem_cache *files_cachep;
>  /* SLAB cache for fs_struct structures (tsk->fs) */
>  struct kmem_cache *fs_cachep;
>
> -/* SLAB cache for vm_area_struct structures */
> -static struct kmem_cache *vm_area_cachep;
> -
>  /* SLAB cache for mm_struct structures (tsk->mm) */
>  static struct kmem_cache *mm_cachep;
>
> -struct vm_area_struct *vm_area_alloc(struct mm_struct *mm)
> -{
> -	struct vm_area_struct *vma;
> -
> -	vma = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);
> -	if (!vma)
> -		return NULL;
> -
> -	vma_init(vma, mm);
> -
> -	return vma;
> -}
> -
> -static void vm_area_init_from(const struct vm_area_struct *src,
> -			      struct vm_area_struct *dest)
> -{
> -	dest->vm_mm = src->vm_mm;
> -	dest->vm_ops = src->vm_ops;
> -	dest->vm_start = src->vm_start;
> -	dest->vm_end = src->vm_end;
> -	dest->anon_vma = src->anon_vma;
> -	dest->vm_pgoff = src->vm_pgoff;
> -	dest->vm_file = src->vm_file;
> -	dest->vm_private_data = src->vm_private_data;
> -	vm_flags_init(dest, src->vm_flags);
> -	memcpy(&dest->vm_page_prot, &src->vm_page_prot,
> -	       sizeof(dest->vm_page_prot));
> -	/*
> -	 * src->shared.rb may be modified concurrently when called from
> -	 * dup_mmap(), but the clone will reinitialize it.
> -	 */
> -	data_race(memcpy(&dest->shared, &src->shared, sizeof(dest->shared)));
> -	memcpy(&dest->vm_userfaultfd_ctx, &src->vm_userfaultfd_ctx,
> -	       sizeof(dest->vm_userfaultfd_ctx));
> -#ifdef CONFIG_ANON_VMA_NAME
> -	dest->anon_name = src->anon_name;
> -#endif
> -#ifdef CONFIG_SWAP
> -	memcpy(&dest->swap_readahead_info, &src->swap_readahead_info,
> -	       sizeof(dest->swap_readahead_info));
> -#endif
> -#ifndef CONFIG_MMU
> -	dest->vm_region = src->vm_region;
> -#endif
> -#ifdef CONFIG_NUMA
> -	dest->vm_policy = src->vm_policy;
> -#endif
> -}
> -
> -struct vm_area_struct *vm_area_dup(struct vm_area_struct *orig)
> -{
> -	struct vm_area_struct *new = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);
> -
> -	if (!new)
> -		return NULL;
> -
> -	ASSERT_EXCLUSIVE_WRITER(orig->vm_flags);
> -	ASSERT_EXCLUSIVE_WRITER(orig->vm_file);
> -	vm_area_init_from(orig, new);
> -	vma_lock_init(new, true);
> -	INIT_LIST_HEAD(&new->anon_vma_chain);
> -	vma_numab_state_init(new);
> -	dup_anon_vma_name(orig, new);
> -
> -	return new;
> -}
> -
> -void vm_area_free(struct vm_area_struct *vma)
> -{
> -	/* The vma should be detached while being destroyed. */
> -	vma_assert_detached(vma);
> -	vma_numab_state_free(vma);
> -	free_anon_vma_name(vma);
> -	kmem_cache_free(vm_area_cachep, vma);
> -}
> -
>  static void account_kernel_stack(struct task_struct *tsk, int account)
>  {
>  	if (IS_ENABLED(CONFIG_VMAP_STACK)) {
> @@ -3033,11 +2954,6 @@ void __init mm_cache_init(void)
>
>  void __init proc_caches_init(void)
>  {
> -	struct kmem_cache_args args = {
> -		.use_freeptr_offset = true,
> -		.freeptr_offset = offsetof(struct vm_area_struct, vm_freeptr),
> -	};
> -
>  	sighand_cachep = kmem_cache_create("sighand_cache",
>  			sizeof(struct sighand_struct), 0,
>  			SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_TYPESAFE_BY_RCU|
> @@ -3054,10 +2970,6 @@ void __init proc_caches_init(void)
>  			sizeof(struct fs_struct), 0,
>  			SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT,
>  			NULL);
> -	vm_area_cachep = kmem_cache_create("vm_area_struct",
> -			sizeof(struct vm_area_struct), &args,
> -			SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_TYPESAFE_BY_RCU|
> -			SLAB_ACCOUNT);
>  	mmap_init();
>  	nsproxy_cache_init();
>  }
> diff --git a/mm/Makefile b/mm/Makefile
> index 15a901bb431a..690ddcf7d9a1 100644
> --- a/mm/Makefile
> +++ b/mm/Makefile
> @@ -55,7 +55,7 @@ obj-y			:= filemap.o mempool.o oom_kill.o fadvise.o \
>  			   mm_init.o percpu.o slab_common.o \
>  			   compaction.o show_mem.o \
>  			   interval_tree.o list_lru.o workingset.o \
> -			   debug.o gup.o mmap_lock.o $(mmu-y)
> +			   debug.o gup.o mmap_lock.o vma_init.o $(mmu-y)
>
>  # Give 'page_alloc' its own module-parameter namespace
>  page-alloc-y := page_alloc.o
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 5259df031e15..81dd962a1cfc 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -1554,7 +1554,7 @@ static const struct ctl_table mmap_table[] = {
>  #endif /* CONFIG_SYSCTL */
>
>  /*
> - * initialise the percpu counter for VM
> + * initialise the percpu counter for VM, initialise VMA state.
>   */
>  void __init mmap_init(void)
>  {
> @@ -1565,6 +1565,7 @@ void __init mmap_init(void)
>  #ifdef CONFIG_SYSCTL
>  	register_sysctl_init("vm", mmap_table);
>  #endif
> +	vma_state_init();
>  }
>
>  /*
> diff --git a/mm/nommu.c b/mm/nommu.c
> index a142fc258d39..0bf4849b8204 100644
> --- a/mm/nommu.c
> +++ b/mm/nommu.c
> @@ -399,7 +399,8 @@ static const struct ctl_table nommu_table[] = {
>  };
>
>  /*
> - * initialise the percpu counter for VM and region record slabs
> + * initialise the percpu counter for VM and region record slabs, initialise VMA
> + * state.
>   */
>  void __init mmap_init(void)
>  {
> @@ -409,6 +410,7 @@ void __init mmap_init(void)
>  	VM_BUG_ON(ret);
>  	vm_region_jar = KMEM_CACHE(vm_region, SLAB_PANIC|SLAB_ACCOUNT);
>  	register_sysctl_init("vm", nommu_table);
> +	vma_state_init();
>  }
>
>  /*
> diff --git a/mm/vma.h b/mm/vma.h
> index 94307a2e4ab6..4a1e1768ca46 100644
> --- a/mm/vma.h
> +++ b/mm/vma.h
> @@ -548,8 +548,15 @@ int expand_downwards(struct vm_area_struct *vma, unsigned long address);
>
>  int __vm_munmap(unsigned long start, size_t len, bool unlock);
>
> +
>  int insert_vm_struct(struct mm_struct *mm, struct vm_area_struct *vma);
>
> +/* vma_init.h, shared between CONFIG_MMU and nommu. */
> +void __init vma_state_init(void);
> +struct vm_area_struct *vm_area_alloc(struct mm_struct *mm);
> +struct vm_area_struct *vm_area_dup(struct vm_area_struct *orig);
> +void vm_area_free(struct vm_area_struct *vma);
> +
>  /* vma_exec.h */
>  #ifdef CONFIG_MMU
>  int create_init_stack_vma(struct mm_struct *mm, struct vm_area_struct **vmap,
> diff --git a/mm/vma_init.c b/mm/vma_init.c
> new file mode 100644
> index 000000000000..967ca8517986
> --- /dev/null
> +++ b/mm/vma_init.c
> @@ -0,0 +1,101 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +
> +/*
> + * Functions for initialisaing, allocating, freeing and duplicating VMAs. Shared
> + * between CONFIG_MMU and non-CONFIG_MMU kernel configurations.
> + */
> +
> +#include "vma_internal.h"
> +#include "vma.h"
> +
> +/* SLAB cache for vm_area_struct structures */
> +static struct kmem_cache *vm_area_cachep;
> +
> +void __init vma_state_init(void)
> +{
> +	struct kmem_cache_args args = {
> +		.use_freeptr_offset = true,
> +		.freeptr_offset = offsetof(struct vm_area_struct, vm_freeptr),
> +	};
> +
> +	vm_area_cachep = kmem_cache_create("vm_area_struct",
> +			sizeof(struct vm_area_struct), &args,
> +			SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_TYPESAFE_BY_RCU|
> +			SLAB_ACCOUNT);
> +}
> +
> +struct vm_area_struct *vm_area_alloc(struct mm_struct *mm)
> +{
> +	struct vm_area_struct *vma;
> +
> +	vma = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);
> +	if (!vma)
> +		return NULL;
> +
> +	vma_init(vma, mm);
> +
> +	return vma;
> +}
> +
> +static void vm_area_init_from(const struct vm_area_struct *src,
> +			      struct vm_area_struct *dest)
> +{
> +	dest->vm_mm = src->vm_mm;
> +	dest->vm_ops = src->vm_ops;
> +	dest->vm_start = src->vm_start;
> +	dest->vm_end = src->vm_end;
> +	dest->anon_vma = src->anon_vma;
> +	dest->vm_pgoff = src->vm_pgoff;
> +	dest->vm_file = src->vm_file;
> +	dest->vm_private_data = src->vm_private_data;
> +	vm_flags_init(dest, src->vm_flags);
> +	memcpy(&dest->vm_page_prot, &src->vm_page_prot,
> +	       sizeof(dest->vm_page_prot));
> +	/*
> +	 * src->shared.rb may be modified concurrently when called from
> +	 * dup_mmap(), but the clone will reinitialize it.
> +	 */
> +	data_race(memcpy(&dest->shared, &src->shared, sizeof(dest->shared)));
> +	memcpy(&dest->vm_userfaultfd_ctx, &src->vm_userfaultfd_ctx,
> +	       sizeof(dest->vm_userfaultfd_ctx));
> +#ifdef CONFIG_ANON_VMA_NAME
> +	dest->anon_name = src->anon_name;
> +#endif
> +#ifdef CONFIG_SWAP
> +	memcpy(&dest->swap_readahead_info, &src->swap_readahead_info,
> +	       sizeof(dest->swap_readahead_info));
> +#endif
> +#ifndef CONFIG_MMU
> +	dest->vm_region = src->vm_region;
> +#endif
> +#ifdef CONFIG_NUMA
> +	dest->vm_policy = src->vm_policy;
> +#endif
> +}
> +
> +struct vm_area_struct *vm_area_dup(struct vm_area_struct *orig)
> +{
> +	struct vm_area_struct *new = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);
> +
> +	if (!new)
> +		return NULL;
> +
> +	ASSERT_EXCLUSIVE_WRITER(orig->vm_flags);
> +	ASSERT_EXCLUSIVE_WRITER(orig->vm_file);
> +	vm_area_init_from(orig, new);
> +	vma_lock_init(new, true);
> +	INIT_LIST_HEAD(&new->anon_vma_chain);
> +	vma_numab_state_init(new);
> +	dup_anon_vma_name(orig, new);
> +
> +	return new;
> +}
> +
> +void vm_area_free(struct vm_area_struct *vma)
> +{
> +	/* The vma should be detached while being destroyed. */
> +	vma_assert_detached(vma);
> +	vma_numab_state_free(vma);
> +	free_anon_vma_name(vma);
> +	kmem_cache_free(vm_area_cachep, vma);
> +}
> diff --git a/tools/testing/vma/Makefile b/tools/testing/vma/Makefile
> index 624040fcf193..66f3831a668f 100644
> --- a/tools/testing/vma/Makefile
> +++ b/tools/testing/vma/Makefile
> @@ -9,7 +9,7 @@ include ../shared/shared.mk
>  OFILES = $(SHARED_OFILES) vma.o maple-shim.o
>  TARGETS = vma
>
> -vma.o: vma.c vma_internal.h ../../../mm/vma.c ../../../mm/vma_exec.c ../../../mm/vma.h
> +vma.o: vma.c vma_internal.h ../../../mm/vma.c ../../../mm/vma_init.c ../../../mm/vma_exec.c ../../../mm/vma.h
>
>  vma:	$(OFILES)
>  	$(CC) $(CFLAGS) -o $@ $(OFILES) $(LDLIBS)
> diff --git a/tools/testing/vma/vma.c b/tools/testing/vma/vma.c
> index 5832ae5d797d..2be7597a2ac2 100644
> --- a/tools/testing/vma/vma.c
> +++ b/tools/testing/vma/vma.c
> @@ -28,6 +28,7 @@ unsigned long stack_guard_gap = 256UL<<PAGE_SHIFT;
>   * Directly import the VMA implementation here. Our vma_internal.h wrapper
>   * provides userland-equivalent functionality for everything vma.c uses.
>   */
> +#include "../../../mm/vma_init.c"
>  #include "../../../mm/vma_exec.c"
>  #include "../../../mm/vma.c"
>
> @@ -91,6 +92,12 @@ static int attach_vma(struct mm_struct *mm, struct vm_area_struct *vma)
>  	return res;
>  }
>
> +static void detach_free_vma(struct vm_area_struct *vma)
> +{
> +	vma_mark_detached(vma);
> +	vm_area_free(vma);
> +}
> +
>  /* Helper function to allocate a VMA and link it to the tree. */
>  static struct vm_area_struct *alloc_and_link_vma(struct mm_struct *mm,
>  						 unsigned long start,
> @@ -104,7 +111,7 @@ static struct vm_area_struct *alloc_and_link_vma(struct mm_struct *mm,
>  		return NULL;
>
>  	if (attach_vma(mm, vma)) {
> -		vm_area_free(vma);
> +		detach_free_vma(vma);
>  		return NULL;
>  	}
>
> @@ -249,7 +256,7 @@ static int cleanup_mm(struct mm_struct *mm, struct vma_iterator *vmi)
>
>  	vma_iter_set(vmi, 0);
>  	for_each_vma(*vmi, vma) {
> -		vm_area_free(vma);
> +		detach_free_vma(vma);
>  		count++;
>  	}
>
> @@ -319,7 +326,7 @@ static bool test_simple_merge(void)
>  	ASSERT_EQ(vma->vm_pgoff, 0);
>  	ASSERT_EQ(vma->vm_flags, flags);
>
> -	vm_area_free(vma);
> +	detach_free_vma(vma);
>  	mtree_destroy(&mm.mm_mt);
>
>  	return true;
> @@ -361,7 +368,7 @@ static bool test_simple_modify(void)
>  	ASSERT_EQ(vma->vm_end, 0x1000);
>  	ASSERT_EQ(vma->vm_pgoff, 0);
>
> -	vm_area_free(vma);
> +	detach_free_vma(vma);
>  	vma_iter_clear(&vmi);
>
>  	vma = vma_next(&vmi);
> @@ -370,7 +377,7 @@ static bool test_simple_modify(void)
>  	ASSERT_EQ(vma->vm_end, 0x2000);
>  	ASSERT_EQ(vma->vm_pgoff, 1);
>
> -	vm_area_free(vma);
> +	detach_free_vma(vma);
>  	vma_iter_clear(&vmi);
>
>  	vma = vma_next(&vmi);
> @@ -379,7 +386,7 @@ static bool test_simple_modify(void)
>  	ASSERT_EQ(vma->vm_end, 0x3000);
>  	ASSERT_EQ(vma->vm_pgoff, 2);
>
> -	vm_area_free(vma);
> +	detach_free_vma(vma);
>  	mtree_destroy(&mm.mm_mt);
>
>  	return true;
> @@ -407,7 +414,7 @@ static bool test_simple_expand(void)
>  	ASSERT_EQ(vma->vm_end, 0x3000);
>  	ASSERT_EQ(vma->vm_pgoff, 0);
>
> -	vm_area_free(vma);
> +	detach_free_vma(vma);
>  	mtree_destroy(&mm.mm_mt);
>
>  	return true;
> @@ -428,7 +435,7 @@ static bool test_simple_shrink(void)
>  	ASSERT_EQ(vma->vm_end, 0x1000);
>  	ASSERT_EQ(vma->vm_pgoff, 0);
>
> -	vm_area_free(vma);
> +	detach_free_vma(vma);
>  	mtree_destroy(&mm.mm_mt);
>
>  	return true;
> @@ -619,7 +626,7 @@ static bool test_merge_new(void)
>  		ASSERT_EQ(vma->vm_pgoff, 0);
>  		ASSERT_EQ(vma->anon_vma, &dummy_anon_vma);
>
> -		vm_area_free(vma);
> +		detach_free_vma(vma);
>  		count++;
>  	}
>
> @@ -1668,6 +1675,7 @@ int main(void)
>  	int num_tests = 0, num_fail = 0;
>
>  	maple_tree_init();
> +	vma_state_init();
>
>  #define TEST(name)							\
>  	do {								\
> diff --git a/tools/testing/vma/vma_internal.h b/tools/testing/vma/vma_internal.h
> index 32e990313158..198abe66de5a 100644
> --- a/tools/testing/vma/vma_internal.h
> +++ b/tools/testing/vma/vma_internal.h
> @@ -155,6 +155,10 @@ typedef __bitwise unsigned int vm_fault_t;
>   */
>  #define pr_warn_once pr_err
>
> +#define data_race(expr) expr
> +
> +#define ASSERT_EXCLUSIVE_WRITER(x)
> +
>  struct kref {
>  	refcount_t refcount;
>  };
> @@ -255,6 +259,8 @@ struct file {
>
>  #define VMA_LOCK_OFFSET	0x40000000
>
> +typedef struct { unsigned long v; } freeptr_t;
> +
>  struct vm_area_struct {
>  	/* The first cache line has the info for VMA tree walking. */
>
> @@ -264,9 +270,7 @@ struct vm_area_struct {
>  			unsigned long vm_start;
>  			unsigned long vm_end;
>  		};
> -#ifdef CONFIG_PER_VMA_LOCK
> -		struct rcu_head vm_rcu;	/* Used for deferred freeing. */
> -#endif
> +		freeptr_t vm_freeptr; /* Pointer used by SLAB_TYPESAFE_BY_RCU */
>  	};
>
>  	struct mm_struct *vm_mm;	/* The address space we belong to. */
> @@ -463,6 +467,65 @@ struct pagetable_move_control {
>  		.len_in = len_,						\
>  	}
>
> +struct kmem_cache_args {
> +	/**
> +	 * @align: The required alignment for the objects.
> +	 *
> +	 * %0 means no specific alignment is requested.
> +	 */
> +	unsigned int align;
> +	/**
> +	 * @useroffset: Usercopy region offset.
> +	 *
> +	 * %0 is a valid offset, when @usersize is non-%0
> +	 */
> +	unsigned int useroffset;
> +	/**
> +	 * @usersize: Usercopy region size.
> +	 *
> +	 * %0 means no usercopy region is specified.
> +	 */
> +	unsigned int usersize;
> +	/**
> +	 * @freeptr_offset: Custom offset for the free pointer
> +	 * in &SLAB_TYPESAFE_BY_RCU caches
> +	 *
> +	 * By default &SLAB_TYPESAFE_BY_RCU caches place the free pointer
> +	 * outside of the object. This might cause the object to grow in size.
> +	 * Cache creators that have a reason to avoid this can specify a custom
> +	 * free pointer offset in their struct where the free pointer will be
> +	 * placed.
> +	 *
> +	 * Note that placing the free pointer inside the object requires the
> +	 * caller to ensure that no fields are invalidated that are required to
> +	 * guard against object recycling (See &SLAB_TYPESAFE_BY_RCU for
> +	 * details).
> +	 *
> +	 * Using %0 as a value for @freeptr_offset is valid. If @freeptr_offset
> +	 * is specified, %use_freeptr_offset must be set %true.
> +	 *
> +	 * Note that @ctor currently isn't supported with custom free pointers
> +	 * as a @ctor requires an external free pointer.
> +	 */
> +	unsigned int freeptr_offset;
> +	/**
> +	 * @use_freeptr_offset: Whether a @freeptr_offset is used.
> +	 */
> +	bool use_freeptr_offset;
> +	/**
> +	 * @ctor: A constructor for the objects.
> +	 *
> +	 * The constructor is invoked for each object in a newly allocated slab
> +	 * page. It is the cache user's responsibility to free object in the
> +	 * same state as after calling the constructor, or deal appropriately
> +	 * with any differences between a freshly constructed and a reallocated
> +	 * object.
> +	 *
> +	 * %NULL means no constructor.
> +	 */
> +	void (*ctor)(void *);
> +};
> +
>  static inline void vma_iter_invalidate(struct vma_iterator *vmi)
>  {
>  	mas_pause(&vmi->mas);
> @@ -547,31 +610,38 @@ static inline void vma_init(struct vm_area_struct *vma, struct mm_struct *mm)
>  	vma->vm_lock_seq = UINT_MAX;
>  }
>
> -static inline struct vm_area_struct *vm_area_alloc(struct mm_struct *mm)
> -{
> -	struct vm_area_struct *vma = calloc(1, sizeof(struct vm_area_struct));
> +struct kmem_cache {
> +	const char *name;
> +	size_t object_size;
> +	struct kmem_cache_args *args;
> +};
>
> -	if (!vma)
> -		return NULL;
> +static inline struct kmem_cache *__kmem_cache_create(const char *name,
> +						     size_t object_size,
> +						     struct kmem_cache_args *args)
> +{
> +	struct kmem_cache *ret = malloc(sizeof(struct kmem_cache));
>
> -	vma_init(vma, mm);
> +	ret->name = name;
> +	ret->object_size = object_size;
> +	ret->args = args;
>
> -	return vma;
> +	return ret;
>  }
>
> -static inline struct vm_area_struct *vm_area_dup(struct vm_area_struct *orig)
> -{
> -	struct vm_area_struct *new = calloc(1, sizeof(struct vm_area_struct));
> +#define kmem_cache_create(__name, __object_size, __args, ...)           \
> +	__kmem_cache_create((__name), (__object_size), (__args))
>
> -	if (!new)
> -		return NULL;
> +static inline void *kmem_cache_alloc(struct kmem_cache *s, gfp_t gfpflags)
> +{
> +	(void)gfpflags;
>
> -	memcpy(new, orig, sizeof(*new));
> -	refcount_set(&new->vm_refcnt, 0);
> -	new->vm_lock_seq = UINT_MAX;
> -	INIT_LIST_HEAD(&new->anon_vma_chain);
> +	return calloc(s->object_size, 1);
> +}
>
> -	return new;
> +static inline void kmem_cache_free(struct kmem_cache *s, void *x)
> +{
> +	free(x);
>  }
>
>  /*
> @@ -738,11 +808,6 @@ static inline void mpol_put(struct mempolicy *)
>  {
>  }
>
> -static inline void vm_area_free(struct vm_area_struct *vma)
> -{
> -	free(vma);
> -}
> -
>  static inline void lru_add_drain(void)
>  {
>  }
> @@ -1312,4 +1377,32 @@ static inline void ksm_exit(struct mm_struct *mm)
>  	(void)mm;
>  }
>
> +static inline void vma_lock_init(struct vm_area_struct *vma, bool reset_refcnt)
> +{
> +	(void)vma;
> +	(void)reset_refcnt;
> +}
> +
> +static inline void vma_numab_state_init(struct vm_area_struct *vma)
> +{
> +	(void)vma;
> +}
> +
> +static inline void vma_numab_state_free(struct vm_area_struct *vma)
> +{
> +	(void)vma;
> +}
> +
> +static inline void dup_anon_vma_name(struct vm_area_struct *orig_vma,
> +				     struct vm_area_struct *new_vma)
> +{
> +	(void)orig_vma;
> +	(void)new_vma;
> +}
> +
> +static inline void free_anon_vma_name(struct vm_area_struct *vma)
> +{
> +	(void)vma;
> +}
> +
>  #endif	/* __MM_VMA_INTERNAL_H */
> --
> 2.49.0
>

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