[PATCH v3 04/11] mm: vmalloc: Remove global vmap_area_root rb-tree

Uladzislau Rezki (Sony)
2024-01-02T18:46:42Z

Store allocated objects in a separate nodes. A va->va_start
address is converted into a correct node where it should
be placed and resided. An addr_to_node() function is used
to do a proper address conversion to determine a node that
contains a VA.

Such approach balances VAs across nodes as a result an access
becomes scalable. Number of nodes in a system depends on number
of CPUs.

Please note:

1. As of now allocated VAs are bound to a node-0. It means the
patch does not give any difference comparing with a current
behavior;

2. The global vmap_area_lock, vmap_area_root are removed as there
is no need in it anymore. The vmap_area_list is still kept and
is _empty_. It is exported for a kexec only;

3. The vmallocinfo and vread() have to be reworked to be able to
handle multiple nodes.

Reviewed-by: Baoquan He <bhe@redhat.com>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
---
mm/vmalloc.c | 240 +++++++++++++++++++++++++++++++++++++--------------
1 file changed, 173 insertions(+), 67 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 06bd843d18ae..786ecb18ae22 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -728,11 +728,9 @@ EXPORT_SYMBOL(vmalloc_to_pfn);
#define DEBUG_AUGMENT_LOWEST_MATCH_CHECK 0

-static DEFINE_SPINLOCK(vmap_area_lock);
static DEFINE_SPINLOCK(free_vmap_area_lock);
/* Export for kexec only */
LIST_HEAD(vmap_area_list);
-static struct rb_root vmap_area_root = RB_ROOT;
static bool vmap_initialized __read_mostly;

static struct rb_root purge_vmap_area_root = RB_ROOT;
@@ -772,6 +770,38 @@ static struct rb_root free_vmap_area_root = RB_ROOT;
*/
static DEFINE_PER_CPU(struct vmap_area *, ne_fit_preload_node);

+/*
+ * An effective vmap-node logic. Users make use of nodes instead
+ * of a global heap. It allows to balance an access and mitigate
+ * contention.
+ */
+struct rb_list {
+ struct rb_root root;
+ struct list_head head;
+ spinlock_t lock;
+};
+
+static struct vmap_node {
+ /* Bookkeeping data of this node. */
+ struct rb_list busy;
+} single;
+
+static struct vmap_node *vmap_nodes = &single;
+static __read_mostly unsigned int nr_vmap_nodes = 1;
+static __read_mostly unsigned int vmap_zone_size = 1;
+
+static inline unsigned int
+addr_to_node_id(unsigned long addr)
+{
+ return (addr / vmap_zone_size) % nr_vmap_nodes;
+}
+
+static inline struct vmap_node *
+addr_to_node(unsigned long addr)
+{
+ return &vmap_nodes[addr_to_node_id(addr)];
+}
+
static __always_inline unsigned long
va_size(struct vmap_area *va)
{
@@ -803,10 +833,11 @@ unsigned long vmalloc_nr_pages(void)
}

/* Look up the first VA which satisfies addr < va_end, NULL if none. */
-static struct vmap_area *find_vmap_area_exceed_addr(unsigned long addr)
+static struct vmap_area *
+find_vmap_area_exceed_addr(unsigned long addr, struct rb_root *root)
{
struct vmap_area *va = NULL;
- struct rb_node *n = vmap_area_root.rb_node;
+ struct rb_node *n = root->rb_node;

addr = (unsigned long)kasan_reset_tag((void *)addr);

@@ -1552,12 +1583,14 @@ __alloc_vmap_area(struct rb_root *root, struct list_head *head,
*/
static void free_vmap_area(struct vmap_area *va)
{
+ struct vmap_node *vn = addr_to_node(va->va_start);
+
/*
* Remove from the busy tree/list.
*/
- spin_lock(&vmap_area_lock);
- unlink_va(va, &vmap_area_root);
- spin_unlock(&vmap_area_lock);
+ spin_lock(&vn->busy.lock);
+ unlink_va(va, &vn->busy.root);
+ spin_unlock(&vn->busy.lock);

/*
* Insert/Merge it back to the free tree/list.
@@ -1600,6 +1633,7 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,
int node, gfp_t gfp_mask,
unsigned long va_flags)
{
+ struct vmap_node *vn;
struct vmap_area *va;
unsigned long freed;
unsigned long addr;
@@ -1645,9 +1679,11 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,
va->vm = NULL;
va->flags = va_flags;

- spin_lock(&vmap_area_lock);
- insert_vmap_area(va, &vmap_area_root, &vmap_area_list);
- spin_unlock(&vmap_area_lock);
+ vn = addr_to_node(va->va_start);
+
+ spin_lock(&vn->busy.lock);
+ insert_vmap_area(va, &vn->busy.root, &vn->busy.head);
+ spin_unlock(&vn->busy.lock);

BUG_ON(!IS_ALIGNED(va->va_start, align));
BUG_ON(va->va_start < vstart);
@@ -1871,26 +1907,61 @@ static void free_unmap_vmap_area(struct vmap_area *va)

struct vmap_area *find_vmap_area(unsigned long addr)
{
+ struct vmap_node *vn;
struct vmap_area *va;
+ int i, j;

- spin_lock(&vmap_area_lock);
- va = __find_vmap_area(addr, &vmap_area_root);
- spin_unlock(&vmap_area_lock);
+ /*
+ * An addr_to_node_id(addr) converts an address to a node index
+ * where a VA is located. If VA spans several zones and passed
+ * addr is not the same as va->va_start, what is not common, we
+ * may need to scan an extra nodes. See an example:
+ *
+ * <--va-->
+ * -|-----|-----|-----|-----|-
+ * 1 2 0 1
+ *
+ * VA resides in node 1 whereas it spans 1 and 2. If passed
+ * addr is within a second node we should do extra work. We
+ * should mention that it is rare and is a corner case from
+ * the other hand it has to be covered.
+ */
+ i = j = addr_to_node_id(addr);
+ do {
+ vn = &vmap_nodes[i];

- return va;
+ spin_lock(&vn->busy.lock);
+ va = __find_vmap_area(addr, &vn->busy.root);
+ spin_unlock(&vn->busy.lock);
+
+ if (va)
+ return va;
+ } while ((i = (i + 1) % nr_vmap_nodes) != j);
+
+ return NULL;
}

static struct vmap_area *find_unlink_vmap_area(unsigned long addr)
{
+ struct vmap_node *vn;
struct vmap_area *va;
+ int i, j;

- spin_lock(&vmap_area_lock);
- va = __find_vmap_area(addr, &vmap_area_root);
- if (va)
- unlink_va(va, &vmap_area_root);
- spin_unlock(&vmap_area_lock);
+ i = j = addr_to_node_id(addr);
+ do {
+ vn = &vmap_nodes[i];

- return va;
+ spin_lock(&vn->busy.lock);
+ va = __find_vmap_area(addr, &vn->busy.root);
+ if (va)
+ unlink_va(va, &vn->busy.root);
+ spin_unlock(&vn->busy.lock);
+
+ if (va)
+ return va;
+ } while ((i = (i + 1) % nr_vmap_nodes) != j);
+
+ return NULL;
}

/*** Per cpu kva allocator ***/
@@ -2092,6 +2163,7 @@ static void *new_vmap_block(unsigned int order, gfp_t gfp_mask)

static void free_vmap_block(struct vmap_block *vb)
{
+ struct vmap_node *vn;
struct vmap_block *tmp;
struct xarray *xa;

@@ -2099,9 +2171,10 @@ static void free_vmap_block(struct vmap_block *vb)
tmp = xa_erase(xa, addr_to_vb_idx(vb->va->va_start));
BUG_ON(tmp != vb);

- spin_lock(&vmap_area_lock);
- unlink_va(vb->va, &vmap_area_root);
- spin_unlock(&vmap_area_lock);
+ vn = addr_to_node(vb->va->va_start);
+ spin_lock(&vn->busy.lock);
+ unlink_va(vb->va, &vn->busy.root);
+ spin_unlock(&vn->busy.lock);

free_vmap_area_noflush(vb->va);
kfree_rcu(vb, rcu_head);
@@ -2525,9 +2598,11 @@ static inline void setup_vmalloc_vm_locked(struct vm_struct *vm,
static void setup_vmalloc_vm(struct vm_struct *vm, struct vmap_area *va,
unsigned long flags, const void *caller)
{
- spin_lock(&vmap_area_lock);
+ struct vmap_node *vn = addr_to_node(va->va_start);
+
+ spin_lock(&vn->busy.lock);
setup_vmalloc_vm_locked(vm, va, flags, caller);
- spin_unlock(&vmap_area_lock);
+ spin_unlock(&vn->busy.lock);
}

static void clear_vm_uninitialized_flag(struct vm_struct *vm)
@@ -3715,6 +3790,7 @@ static size_t vmap_ram_vread_iter(struct iov_iter *iter, const char *addr,
*/
long vread_iter(struct iov_iter *iter, const char *addr, size_t count)
{
+ struct vmap_node *vn;
struct vmap_area *va;
struct vm_struct *vm;
char *vaddr;
@@ -3728,8 +3804,11 @@ long vread_iter(struct iov_iter *iter, const char *addr, size_t count)

remains = count;

- spin_lock(&vmap_area_lock);
- va = find_vmap_area_exceed_addr((unsigned long)addr);
+ /* Hooked to node_0 so far. */
+ vn = addr_to_node(0);
+ spin_lock(&vn->busy.lock);
+
+ va = find_vmap_area_exceed_addr((unsigned long)addr, &vn->busy.root);
if (!va)
goto finished_zero;

@@ -3737,7 +3816,7 @@ long vread_iter(struct iov_iter *iter, const char *addr, size_t count)
if ((unsigned long)addr + remains <= va->va_start)
goto finished_zero;

- list_for_each_entry_from(va, &vmap_area_list, list) {
+ list_for_each_entry_from(va, &vn->busy.head, list) {
size_t copied;

if (remains == 0)
@@ -3796,12 +3875,12 @@ long vread_iter(struct iov_iter *iter, const char *addr, size_t count)
}

finished_zero:
- spin_unlock(&vmap_area_lock);
+ spin_unlock(&vn->busy.lock);
/* zero-fill memory holes */
return count - remains + zero_iter(iter, remains);
finished:
/* Nothing remains, or We couldn't copy/zero everything. */
- spin_unlock(&vmap_area_lock);
+ spin_unlock(&vn->busy.lock);

return count - remains;
}
@@ -4135,14 +4214,15 @@ struct vm_struct **pcpu_get_vm_areas(const unsigned long *offsets,
}

/* insert all vm's */
- spin_lock(&vmap_area_lock);
for (area = 0; area < nr_vms; area++) {
- insert_vmap_area(vas[area], &vmap_area_root, &vmap_area_list);
+ struct vmap_node *vn = addr_to_node(vas[area]->va_start);

+ spin_lock(&vn->busy.lock);
+ insert_vmap_area(vas[area], &vn->busy.root, &vn->busy.head);
setup_vmalloc_vm_locked(vms[area], vas[area], VM_ALLOC,
pcpu_get_vm_areas);
+ spin_unlock(&vn->busy.lock);
}
- spin_unlock(&vmap_area_lock);

/*
* Mark allocated areas as accessible. Do it now as a best-effort
@@ -4253,55 +4333,57 @@ bool vmalloc_dump_obj(void *object)
{
void *objp = (void *)PAGE_ALIGN((unsigned long)object);
const void *caller;
- struct vm_struct *vm;
struct vmap_area *va;
+ struct vmap_node *vn;
unsigned long addr;
unsigned int nr_pages;
+ bool success = false;

- if (!spin_trylock(&vmap_area_lock))
- return false;
- va = __find_vmap_area((unsigned long)objp, &vmap_area_root);
- if (!va) {
- spin_unlock(&vmap_area_lock);
- return false;
- }
+ vn = addr_to_node((unsigned long)objp);

- vm = va->vm;
- if (!vm) {
- spin_unlock(&vmap_area_lock);
- return false;
+ if (spin_trylock(&vn->busy.lock)) {
+ va = __find_vmap_area(addr, &vn->busy.root);
+
+ if (va && va->vm) {
+ addr = (unsigned long)va->vm->addr;
+ caller = va->vm->caller;
+ nr_pages = va->vm->nr_pages;
+ success = true;
+ }
+
+ spin_unlock(&vn->busy.lock);
}
- addr = (unsigned long)vm->addr;
- caller = vm->caller;
- nr_pages = vm->nr_pages;
- spin_unlock(&vmap_area_lock);
- pr_cont(" %u-page vmalloc region starting at %#lx allocated at %pS\n",
- nr_pages, addr, caller);
- return true;
+
+ if (success)
+ pr_cont(" %u-page vmalloc region starting at %#lx allocated at %pS\n",
+ nr_pages, addr, caller);
+
+ return success;
}
#endif

#ifdef CONFIG_PROC_FS
static void *s_start(struct seq_file *m, loff_t *pos)
- __acquires(&vmap_purge_lock)
- __acquires(&vmap_area_lock)
{
+ struct vmap_node *vn = addr_to_node(0);
+
mutex_lock(&vmap_purge_lock);
- spin_lock(&vmap_area_lock);
+ spin_lock(&vn->busy.lock);

- return seq_list_start(&vmap_area_list, *pos);
+ return seq_list_start(&vn->busy.head, *pos);
}

static void *s_next(struct seq_file *m, void *p, loff_t *pos)
{
- return seq_list_next(p, &vmap_area_list, pos);
+ struct vmap_node *vn = addr_to_node(0);
+ return seq_list_next(p, &vn->busy.head, pos);
}

static void s_stop(struct seq_file *m, void *p)
- __releases(&vmap_area_lock)
- __releases(&vmap_purge_lock)
{
- spin_unlock(&vmap_area_lock);
+ struct vmap_node *vn = addr_to_node(0);
+
+ spin_unlock(&vn->busy.lock);
mutex_unlock(&vmap_purge_lock);
}

@@ -4344,9 +4426,11 @@ static void show_purge_info(struct seq_file *m)

static int s_show(struct seq_file *m, void *p)
{
+ struct vmap_node *vn;
struct vmap_area *va;
struct vm_struct *v;

+ vn = addr_to_node(0);
va = list_entry(p, struct vmap_area, list);

if (!va->vm) {
@@ -4397,7 +4481,7 @@ static int s_show(struct seq_file *m, void *p)
* As a final step, dump "unpurged" areas.
*/
final:
- if (list_is_last(&va->list, &vmap_area_list))
+ if (list_is_last(&va->list, &vn->busy.head))
show_purge_info(m);

return 0;
@@ -4428,7 +4512,8 @@ static void vmap_init_free_space(void)
{
unsigned long vmap_start = 1;
const unsigned long vmap_end = ULONG_MAX;
- struct vmap_area *busy, *free;
+ struct vmap_area *free;
+ struct vm_struct *busy;

/*
* B F B B B F
@@ -4436,12 +4521,12 @@ static void vmap_init_free_space(void)
* | The KVA space |
* |<--------------------------------->|
*/
- list_for_each_entry(busy, &vmap_area_list, list) {
- if (busy->va_start - vmap_start > 0) {
+ for (busy = vmlist; busy; busy = busy->next) {
+ if ((unsigned long) busy->addr - vmap_start > 0) {
free = kmem_cache_zalloc(vmap_area_cachep, GFP_NOWAIT);
if (!WARN_ON_ONCE(!free)) {
free->va_start = vmap_start;
- free->va_end = busy->va_start;
+ free->va_end = (unsigned long) busy->addr;

insert_vmap_area_augment(free, NULL,
&free_vmap_area_root,
@@ -4449,7 +4534,7 @@ static void vmap_init_free_space(void)
}
}

- vmap_start = busy->va_end;
+ vmap_start = (unsigned long) busy->addr + busy->size;
}

if (vmap_end - vmap_start > 0) {
@@ -4465,9 +4550,23 @@ static void vmap_init_free_space(void)
}
}

+static void vmap_init_nodes(void)
+{
+ struct vmap_node *vn;
+ int i;
+
+ for (i = 0; i < nr_vmap_nodes; i++) {
+ vn = &vmap_nodes[i];
+ vn->busy.root = RB_ROOT;
+ INIT_LIST_HEAD(&vn->busy.head);
+ spin_lock_init(&vn->busy.lock);
+ }
+}
+
void __init vmalloc_init(void)
{
struct vmap_area *va;
+ struct vmap_node *vn;
struct vm_struct *tmp;
int i;

@@ -4489,6 +4588,11 @@ void __init vmalloc_init(void)
xa_init(&vbq->vmap_blocks);
}

+ /*
+ * Setup nodes before importing vmlist.
+ */
+ vmap_init_nodes();
+
/* Import existing vmlist entries. */
for (tmp = vmlist; tmp; tmp = tmp->next) {
va = kmem_cache_zalloc(vmap_area_cachep, GFP_NOWAIT);
@@ -4498,7 +4602,9 @@ void __init vmalloc_init(void)
va->va_start = (unsigned long)tmp->addr;
va->va_end = va->va_start + tmp->size;
va->vm = tmp;
- insert_vmap_area(va, &vmap_area_root, &vmap_area_list);
+
+ vn = addr_to_node(va->va_start);
+ insert_vmap_area(va, &vn->busy.root, &vn->busy.head);
}

/*
--
2.39.2