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Date: Fri, 4 Nov 2022 17:18:58 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: "zhaoyang.huang" <zhaoyang.huang@...soc.com>,
Christoph Lameter <cl@...ux.com>,
Pekka Enberg <penberg@...nel.org>,
David Rientjes <rientjes@...gle.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Joonsoo Kim <iamjoonsoo.kim@....com>,
Zhaoyang Huang <huangzhaoyang@...il.com>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, ke.wang@...soc.com,
steve.kang@...soc.com, Hyeonggon Yoo <42.hyeyoo@...il.com>
Subject: Re: [RFC PATCH] mm: introduce object accounting via backtrace on slub
On 11/4/22 09:33, zhaoyang.huang wrote:
> From: Zhaoyang Huang <zhaoyang.huang@...soc.com>
>
> Introduce a set of methods to account object via backtrace.
Can you describe what exactly it does, so we don't need to guess from
the source code?
> Signed-off-by: Zhaoyang Huang <zhaoyang.huang@...soc.com>
> ---
> include/linux/slub_def.h | 7 +++
> mm/slub.c | 155 ++++++++++++++++++++++++++++++++++++++++++++++-
> 2 files changed, 161 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/slub_def.h b/include/linux/slub_def.h
> index f9c68a9..c90e5fb 100644
> --- a/include/linux/slub_def.h
> +++ b/include/linux/slub_def.h
> @@ -139,9 +139,16 @@ struct kmem_cache {
> unsigned int useroffset; /* Usercopy region offset */
> unsigned int usersize; /* Usercopy region size */
>
> + struct rb_root user_hash_root;
> +
> struct kmem_cache_node *node[MAX_NUMNODES];
> };
>
> +struct hash_object {
> + int count;
> + depot_stack_handle_t trace_hash;
> + struct rb_node rb_node;
> +};
> #ifdef CONFIG_SYSFS
> #define SLAB_SUPPORTS_SYSFS
> void sysfs_slab_unlink(struct kmem_cache *);
> diff --git a/mm/slub.c b/mm/slub.c
> index 157527d..3ec02ff 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -337,6 +337,7 @@ static inline void stat(const struct kmem_cache *s, enum stat_item si)
> */
> static struct workqueue_struct *flushwq;
>
> +static struct kmem_cache *user_hash_cache;
> /********************************************************************
> * Core slab cache functions
> *******************************************************************/
> @@ -759,12 +760,152 @@ static void set_track_update(struct kmem_cache *s, void *object,
> p->when = jiffies;
> }
>
> +static void store_user_hash(struct kmem_cache *s, void *object,
> + depot_stack_handle_t trace_hash, enum track_item alloc)
> +{
> + struct rb_node *rb_parent;
> + unsigned int trace_hash_parent;
> + struct rb_node **link = &s->user_hash_root.rb_node;
> + struct hash_object *hash_parent = NULL;
> + struct hash_object *hash_object = NULL;
> + unsigned long flags;
> + int count;
> + int nid = slab_nid(virt_to_slab(object));
> + struct kmem_cache_node *n = get_node(s, nid);
> +
> + spin_lock_irqsave(&n->list_lock, flags);
> + while (*link) {
> + rb_parent = *link;
> + hash_parent = rb_entry(rb_parent, struct hash_object, rb_node);
> + trace_hash_parent = hash_parent->trace_hash;
> + if (trace_hash < trace_hash_parent)
> + link = &hash_parent->rb_node.rb_left;
> + else if (trace_hash_parent < trace_hash)
> + link = &hash_parent->rb_node.rb_right;
> + else {
> + hash_object = rb_entry(*link, struct hash_object, rb_node);
> + count = (alloc == TRACK_ALLOC) ? 1 : -1;
> + hash_object->count += count;
> + if (!RB_EMPTY_ROOT(&s->user_hash_root)
> + && !hash_object->count) {
> + rb_erase(&hash_object->rb_node, &s->user_hash_root);
> + kmem_cache_free(user_hash_cache, hash_object);
> + }
> + spin_unlock_irqrestore(&n->list_lock, flags);
> + return;
> + }
> + }
> + spin_unlock_irqrestore(&n->list_lock, flags);
> + /*
> + * hash_object is the 1st node represent this trace_hash
> + * insert it to user_hash_root
> + */
> + hash_object = kmem_cache_alloc(user_hash_cache, GFP_KERNEL);
> + if (!hash_object)
> + return;
> + hash_object->trace_hash = trace_hash;
> + /* add the node to rb tree*/
> + spin_lock_irqsave(&n->list_lock, flags);
> + rb_link_node(&hash_object->rb_node, rb_parent, link);
> + rb_insert_color(&hash_object->rb_node, &s->user_hash_root);
> + spin_unlock_irqrestore(&n->list_lock, flags);
> + return;
> +}
> +
> +static ssize_t backtrace_acc_print(struct file *file, char __user *buf, size_t count, loff_t *ppos)
> +{
> + struct hash_object *object;
> + struct rb_node *rb;
> + unsigned long *entries;
> + unsigned int nr_entries;
> + char *kbuf;
> + int i, ret = 0;
> + unsigned long flags;
> + struct kmem_cache_node *n;
> + enum track_item alloc;
> + int node;
> + struct slab *slab;
> + struct kmem_cache *s = file_inode(file)->i_private;
> +
> + count = min_t(size_t, count, PAGE_SIZE);
> + kbuf = kmalloc(count, GFP_KERNEL);
> + if (!kbuf)
> + return -ENOMEM;
> +
> + /* iterate from node-0 */
> + node = *ppos;
> + if (node >= nr_node_ids)
> + return 0;
> +
> + if ((n = get_node(s, node))) {
> + /* skip empty node */
> + while (!atomic_long_read(&n->nr_slabs)) {
> + if (++node >= nr_node_ids)
> + return 0;
> + n = get_node(s, node);
> + }
> +
> + rb = file->private_data ? (struct rb_node *)file->private_data : rb_first(&s->user_hash_root);
> + /* current node finish, reset rb to next node's root */
> + if(!rb) {
> + ret += snprintf(kbuf + ret, count - ret, "\n");
> + copy_to_user(buf, kbuf, ret);
> + file->private_data = 0;
> + *ppos = ++node;
> + return ret;
> + }
> +
> + spin_lock_irqsave(&n->list_lock, flags);
> + object = rb_entry(rb, struct hash_object, rb_node);
> + if (object) {
> + while (!object->trace_hash || object->count <= 0) {
> + rb = rb_next(rb);
> + object = rb ? rb_entry(rb, struct hash_object, rb_node) : NULL;
> + if (!object) {
> + spin_unlock_irqrestore(&n->list_lock, flags);
> + ret += snprintf(kbuf + ret, count - ret, "\n");
> + copy_to_user(buf, kbuf, ret);
> + file->private_data = 0;
> + *ppos = ++node;
> + kfree(kbuf);
> + return ret;
> + }
> + }
> + nr_entries = stack_depot_fetch(object->trace_hash, &entries);
> + ret += snprintf(kbuf + ret, count - ret, "count %d\n", object->count);
> + if (ret >= count)
> + goto err;
> + for (i = 0; i < nr_entries; i++) {
> + void *ptr = (void *)entries[i];
> + ret += snprintf(kbuf + ret, count - ret, " [<%p>] %pS\n", ptr, ptr);
> + if (ret >= count)
> + goto err;
> + }
> + }
> + file->private_data = (void *)rb_next(rb);
> + spin_unlock_irqrestore(&n->list_lock, flags);
> + *ppos = ++node;
> + if (copy_to_user(buf, kbuf, ret))
> + ret = -EFAULT;
> +
> + kfree(kbuf);
> + return ret;
> +err:
> + spin_unlock_irqrestore(&n->list_lock, flags);
> + kfree(kbuf);
> + return -ENOMEM;
> + }
> + return 0;
> +}
> +
> static __always_inline void set_track(struct kmem_cache *s, void *object,
> enum track_item alloc, unsigned long addr)
> {
> depot_stack_handle_t handle = set_track_prepare();
>
> set_track_update(s, object, alloc, addr, handle);
> + if (strcmp(s->name, "user_hash_cache") != 0)
> + store_user_hash(s, object, handle, alloc);
> }
>
> static void init_tracking(struct kmem_cache *s, void *object)
> @@ -4918,8 +5059,10 @@ int __kmem_cache_create(struct kmem_cache *s, slab_flags_t flags)
> return err;
> }
>
> - if (s->flags & SLAB_STORE_USER)
> + if (s->flags & SLAB_STORE_USER) {
> + s->user_hash_root = RB_ROOT;
> debugfs_slab_add(s);
> + }
>
> return 0;
> }
> @@ -6236,6 +6379,10 @@ static int slab_debug_trace_release(struct inode *inode, struct file *file)
> .release = slab_debug_trace_release,
> };
>
> +static const struct file_operations backtrace_accounting_operations = {
> + .read = backtrace_acc_print,
> +};
> +
> static void debugfs_slab_add(struct kmem_cache *s)
> {
> struct dentry *slab_cache_dir;
> @@ -6250,6 +6397,9 @@ static void debugfs_slab_add(struct kmem_cache *s)
>
> debugfs_create_file("free_traces", 0400,
> slab_cache_dir, s, &slab_debugfs_fops);
> +
> + debugfs_create_file("backtrace_accounting", 0400, NULL, NULL,
> + &backtrace_accounting_operations);
> }
>
> void debugfs_slab_release(struct kmem_cache *s)
> @@ -6261,6 +6411,9 @@ static int __init slab_debugfs_init(void)
> {
> struct kmem_cache *s;
>
> + user_hash_cache = kmem_cache_create("user_hash_cache",
> + sizeof(struct hash_object),
> + 0, 0, NULL);
> slab_debugfs_root = debugfs_create_dir("slab", NULL);
>
> list_for_each_entry(s, &slab_caches, list)
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