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Message-ID: <6d91e7cb-514f-8816-76b1-a70f6891a47a@codeaurora.org>
Date: Tue, 18 May 2021 18:24:48 +0530
From: Faiyaz Mohammed <faiyazm@...eaurora.org>
To: Greg KH <greg@...ah.com>
Cc: cl@...ux.com, penberg@...nel.org, rientjes@...gle.com,
iamjoonsoo.kim@....com, akpm@...ux-foundation.org, vbabka@...e.cz,
linux-mm@...ck.org, linux-kernel@...r.kernel.org,
glittao@...il.com, vinmenon@...eaurora.org
Subject: Re: [PATCH v5] mm: slub: move sysfs slab alloc/free interfaces to
debugfs
On 5/7/2021 5:18 PM, Greg KH wrote:
> On Thu, May 06, 2021 at 03:52:03PM +0530, Faiyaz Mohammed wrote:
>> alloc_calls and free_calls implementation in sysfs have two issues,
>> one is PAGE_SIZE limitiation of sysfs and other is it does not adhere
>> to "one value per file" rule.
>>
>> To overcome this issues, move the alloc_calls and free_calls implemeation
>> to debugfs.
>>
>> Rename the alloc_calls/free_calls to alloc_traces/free_traces,
>> to be inline with what it does.
>>
>> Signed-off-by: Faiyaz Mohammed <faiyazm@...eaurora.org>
>> ---
>> include/linux/slub_def.h | 10 ++
>> mm/slab_common.c | 9 ++
>> mm/slub.c | 362 ++++++++++++++++++++++++++++++++++++-----------
>> 3 files changed, 299 insertions(+), 82 deletions(-)
>>
>> diff --git a/include/linux/slub_def.h b/include/linux/slub_def.h
>> index dcde82a..f8c268d 100644
>> --- a/include/linux/slub_def.h
>> +++ b/include/linux/slub_def.h
>> @@ -110,6 +110,9 @@ struct kmem_cache {
>> #ifdef CONFIG_SYSFS
>> struct kobject kobj; /* For sysfs */
>> #endif
>> +#ifdef CONFIG_SLUB_DEBUG
>> + struct dentry *slab_cache_dentry;
>> +#endif
>> #ifdef CONFIG_SLAB_FREELIST_HARDENED
>> unsigned long random;
>> #endif
>> @@ -159,6 +162,13 @@ static inline void sysfs_slab_release(struct kmem_cache *s)
>> }
>> #endif
>>
>> +#ifdef CONFIG_DEBUG_FS
>> +void debugfs_slab_release(struct kmem_cache *);
>> +#else
>> +static inline void debugfs_slab_release(struct kmem_cache *s)
>> +{
>> +}
>> +#endif
>> void object_err(struct kmem_cache *s, struct page *page,
>> u8 *object, char *reason);
>>
>> diff --git a/mm/slab_common.c b/mm/slab_common.c
>> index f8833d3..f3afe6b 100644
>> --- a/mm/slab_common.c
>> +++ b/mm/slab_common.c
>> @@ -445,6 +445,9 @@ static void slab_caches_to_rcu_destroy_workfn(struct work_struct *work)
>> #else
>> slab_kmem_cache_release(s);
>> #endif
>> +#if defined(CONFIG_DEBUG_FS) && defined(CONFIG_SLUB)
>> + debugfs_slab_release(s);
>> +#endif
>
> If you write your .h files correctly, no need for #ifdef in a .c file.
>
> Please fix up.
>
fixed in new patch and used the single #ifded because
debugfs_slab_release declaration is there in slub_def.h and slab_common
is used for both slab and slub.
Like SLAB_SUPPORTS_SYSFS, SLAB_SUPPORT_DEBUGFS will be not defined if
slab config is used.
>> }
>> }
>>
>> @@ -462,6 +465,9 @@ static int shutdown_cache(struct kmem_cache *s)
>> #ifdef SLAB_SUPPORTS_SYSFS
>> sysfs_slab_unlink(s);
>> #endif
>> +#if defined(CONFIG_DEBUG_FS) && defined(CONFIG_SLUB)
>> + debugfs_slab_release(s);
>> +#endif
>> list_add_tail(&s->list, &slab_caches_to_rcu_destroy);
>> schedule_work(&slab_caches_to_rcu_destroy_work);
>> } else {
>> @@ -472,6 +478,9 @@ static int shutdown_cache(struct kmem_cache *s)
>> #else
>> slab_kmem_cache_release(s);
>> #endif
>> +#if defined(CONFIG_DEBUG_FS) && defined(CONFIG_SLUB)
>> + debugfs_slab_release(s);
>> +#endif
>> }
>>
>> return 0;
>> diff --git a/mm/slub.c b/mm/slub.c
>> index 68123b2..a5347f1 100644
>> --- a/mm/slub.c
>> +++ b/mm/slub.c
>> @@ -36,6 +36,7 @@
>> #include <linux/memcontrol.h>
>> #include <linux/random.h>
>>
>> +#include <linux/debugfs.h>
>> #include <trace/events/kmem.h>
>>
>> #include "internal.h"
>> @@ -225,6 +226,15 @@ static inline int sysfs_slab_alias(struct kmem_cache *s, const char *p)
>> { return 0; }
>> #endif
>>
>> +#ifdef CONFIG_DEBUG_FS
>> +static void debugfs_slab_add(struct kmem_cache *);
>> +static int debugfs_slab_alias(struct kmem_cache *, const char *);
>> +#else
>> +static inline void debugfs_slab_add(struct kmem_cache *s) { }
>> +static inline int debugfs_slab_alias(struct kmem_cache *s, const char *p)
>> + { return 0; }
>> +#endif
>> +
>> static inline void stat(const struct kmem_cache *s, enum stat_item si)
>> {
>> #ifdef CONFIG_SLUB_STATS
>> @@ -4533,6 +4543,8 @@ __kmem_cache_alias(const char *name, unsigned int size, unsigned int align,
>> s->refcount--;
>> s = NULL;
>> }
>> +
>> + debugfs_slab_alias(s, name);
>> }
>>
>> return s;
>> @@ -4554,6 +4566,8 @@ int __kmem_cache_create(struct kmem_cache *s, slab_flags_t flags)
>> if (err)
>> __kmem_cache_release(s);
>>
>> + debugfs_slab_add(s);
>> +
>> return err;
>> }
>>
>> @@ -4694,6 +4708,8 @@ static long validate_slab_cache(struct kmem_cache *s)
>>
>> return count;
>> }
>> +
>> +#ifdef CONFIG_DEBUG_FS
>> /*
>> * Generate lists of code addresses where slabcache objects are allocated
>> * and freed.
>> @@ -4717,6 +4733,9 @@ struct loc_track {
>> struct location *loc;
>> };
>>
>> +static struct dentry *slab_debugfs_root;
>> +struct loc_track t = { 0, 0, NULL };
>> +
>> static void free_loc_track(struct loc_track *t)
>> {
>> if (t->max)
>> @@ -4833,82 +4852,7 @@ static void process_slab(struct loc_track *t, struct kmem_cache *s,
>> add_location(t, s, get_track(s, p, alloc));
>> put_map(map);
>> }
>> -
>> -static int list_locations(struct kmem_cache *s, char *buf,
>> - enum track_item alloc)
>> -{
>> - int len = 0;
>> - unsigned long i;
>> - struct loc_track t = { 0, 0, NULL };
>> - int node;
>> - struct kmem_cache_node *n;
>> -
>> - if (!alloc_loc_track(&t, PAGE_SIZE / sizeof(struct location),
>> - GFP_KERNEL)) {
>> - return sysfs_emit(buf, "Out of memory\n");
>> - }
>> - /* Push back cpu slabs */
>> - flush_all(s);
>> -
>> - for_each_kmem_cache_node(s, node, n) {
>> - unsigned long flags;
>> - struct page *page;
>> -
>> - if (!atomic_long_read(&n->nr_slabs))
>> - continue;
>> -
>> - spin_lock_irqsave(&n->list_lock, flags);
>> - list_for_each_entry(page, &n->partial, slab_list)
>> - process_slab(&t, s, page, alloc);
>> - list_for_each_entry(page, &n->full, slab_list)
>> - process_slab(&t, s, page, alloc);
>> - spin_unlock_irqrestore(&n->list_lock, flags);
>> - }
>> -
>> - for (i = 0; i < t.count; i++) {
>> - struct location *l = &t.loc[i];
>> -
>> - len += sysfs_emit_at(buf, len, "%7ld ", l->count);
>> -
>> - if (l->addr)
>> - len += sysfs_emit_at(buf, len, "%pS", (void *)l->addr);
>> - else
>> - len += sysfs_emit_at(buf, len, "<not-available>");
>> -
>> - if (l->sum_time != l->min_time)
>> - len += sysfs_emit_at(buf, len, " age=%ld/%ld/%ld",
>> - l->min_time,
>> - (long)div_u64(l->sum_time,
>> - l->count),
>> - l->max_time);
>> - else
>> - len += sysfs_emit_at(buf, len, " age=%ld", l->min_time);
>> -
>> - if (l->min_pid != l->max_pid)
>> - len += sysfs_emit_at(buf, len, " pid=%ld-%ld",
>> - l->min_pid, l->max_pid);
>> - else
>> - len += sysfs_emit_at(buf, len, " pid=%ld",
>> - l->min_pid);
>> -
>> - if (num_online_cpus() > 1 &&
>> - !cpumask_empty(to_cpumask(l->cpus)))
>> - len += sysfs_emit_at(buf, len, " cpus=%*pbl",
>> - cpumask_pr_args(to_cpumask(l->cpus)));
>> -
>> - if (nr_online_nodes > 1 && !nodes_empty(l->nodes))
>> - len += sysfs_emit_at(buf, len, " nodes=%*pbl",
>> - nodemask_pr_args(&l->nodes));
>> -
>> - len += sysfs_emit_at(buf, len, "\n");
>> - }
>> -
>> - free_loc_track(&t);
>> - if (!t.count)
>> - len += sysfs_emit_at(buf, len, "No data\n");
>> -
>> - return len;
>> -}
>> +#endif /* CONFIG_DEBUG_FS */
>> #endif /* CONFIG_SLUB_DEBUG */
>>
>> #ifdef SLUB_RESILIENCY_TEST
>> @@ -5360,17 +5304,25 @@ SLAB_ATTR(validate);
>>
>> static ssize_t alloc_calls_show(struct kmem_cache *s, char *buf)
>> {
>> - if (!(s->flags & SLAB_STORE_USER))
>> - return -ENOSYS;
>> - return list_locations(s, buf, TRACK_ALLOC);
>> + int len = 0;
>> +
>> + len += sprintf(buf + len, "Deprecated, use the equvalent under\n");
>> + len += sprintf(buf + len, "/sys/kernel/debug/slab/%s/alloc_traces\n",
>> + s->name);
>> +
>> + return len;
>> }
>> SLAB_ATTR_RO(alloc_calls);
>>
>> static ssize_t free_calls_show(struct kmem_cache *s, char *buf)
>> {
>> - if (!(s->flags & SLAB_STORE_USER))
>> - return -ENOSYS;
>> - return list_locations(s, buf, TRACK_FREE);
>> + int len = 0;
>> +
>> + len += sprintf(buf + len, "Deprecated, use the equvalent under\n");
>> + len += sprintf(buf + len, "/sys/kernel/debug/slab/%s/free_traces\n",
>> + s->name);
>> +
>> + return len;
>> }
>> SLAB_ATTR_RO(free_calls);
>> #endif /* CONFIG_SLUB_DEBUG */
>> @@ -5826,6 +5778,252 @@ static int __init slab_sysfs_init(void)
>> __initcall(slab_sysfs_init);
>> #endif /* CONFIG_SYSFS */
>>
>> +#if defined(CONFIG_SLUB_DEBUG) && defined(CONFIG_DEBUG_FS)
>> +static int debugfs_slab_alias(struct kmem_cache *s, const char *name)
>> +{
>> + struct saved_alias *al;
>> +
>> + if (slab_state == FULL) {
>> + /*
>> + * If we have a leftover link then remove it.
>> + */
>> + debugfs_remove(s->slab_cache_dentry);
>> + s->slab_cache_dentry = debugfs_create_symlink(name, slab_debugfs_root, NULL);
>> + return IS_ERR(s->slab_cache_dentry);
>
> Why do you care if this returned an error or not? No normal code should
> care, please just keep on going.
>
> And are you sure you have to save the dentry? Why not just look it up
> when you want to remove it? That way you save the memory, which for
> slabs, can be a lot, right?
>
>
>
Updated in new patch,
https://lore.kernel.org/linux-mm/1621341949-26762-1-git-send-email-faiyazm@codeaurora.org/T/#u
>> + }
>> +
>> + al = kmalloc(sizeof(struct saved_alias), GFP_KERNEL);
>> + if (!al)
>> + return -ENOMEM;
>> +
>> + al->s = s;
>> + al->name = name;
>> + al->next = alias_list;
>> + alias_list = al;
>> + return 0;
>> +}
>> +
>> +static int slab_debugfs_show(struct seq_file *seq, void *v)
>> +{
>> +
>> + struct location *l;
>> + unsigned int idx = *(unsigned int *)v;
>> +
>> + if (idx < t.count) {
>> + l = &t.loc[idx];
>> +
>> + seq_printf(seq, "%7ld ", l->count);
>> +
>> + if (l->addr)
>> + seq_printf(seq, "%pS", (void *)l->addr);
>> + else
>> + seq_puts(seq, "<not-available>");
>> +
>> + if (l->sum_time != l->min_time) {
>> + seq_printf(seq, " age=%ld/%ld/%ld",
>> + l->min_time,
>> + (long)div_u64(l->sum_time, l->count),
>> + l->max_time);
>> + } else
>> + seq_printf(seq, " age=%ld",
>> + l->min_time);
>> +
>> + if (l->min_pid != l->max_pid)
>> + seq_printf(seq, " pid=%ld-%ld",
>> + l->min_pid, l->max_pid);
>> + else
>> + seq_printf(seq, " pid=%ld",
>> + l->min_pid);
>> +
>> + if (num_online_cpus() > 1 &&
>> + !cpumask_empty(to_cpumask(l->cpus)))
>> + seq_printf(seq, " cpus=%*pbl",
>> + cpumask_pr_args(to_cpumask(l->cpus)));
>> +
>> + if (nr_online_nodes > 1 && !nodes_empty(l->nodes))
>> + seq_printf(seq, " nodes=%*pbl",
>> + nodemask_pr_args(&l->nodes));
>> +
>> + seq_puts(seq, "\n");
>> + }
>> +
>> + if (t.count == 0)
>> + seq_puts(seq, "No data\n");
>> +
>> + return 0;
>> +}
>> +
>> +static void slab_debugfs_stop(struct seq_file *seq, void *v)
>> +{
>> + if (!v && t.max) {
>> + free_loc_track(&t);
>> + t.max = 0;
>> + }
>> +}
>> +
>> +static void *slab_debugfs_next(struct seq_file *seq, void *v, loff_t *ppos)
>> +{
>> + loff_t *spos = v;
>> +
>> + if (*ppos < t.count) {
>> + *spos = *spos + 1;
>> + *ppos = *spos;
>> + return spos;
>> + }
>> +
>> + return NULL;
>> +}
>> +
>> +static void *slab_debugfs_start(struct seq_file *seq, loff_t *ppos)
>> +{
>> + struct kmem_cache_node *n;
>> + struct kmem_cache *s;
>> + enum track_item alloc;
>> + int node;
>> + loff_t *spos = kmalloc(sizeof(loff_t), GFP_KERNEL);
>> +
>> + s = seq->file->f_inode->i_private;
>> +
>> + if (!spos)
>> + return NULL;
>> +
>> + if (!(s->flags & SLAB_STORE_USER))
>> + return ERR_PTR(-EOPNOTSUPP);
>> +
>> + if (*ppos == 0) {
>> +
>> + t.count = 0;
>> + t.max = 0;
>> + t.loc = NULL;
>> + if (strcmp(seq->file->f_path.dentry->d_name.name, "alloc_traces") == 0)
>> + alloc = TRACK_ALLOC;
>> + else
>> + alloc = TRACK_FREE;
>> +
>> + if (!alloc_loc_track(&t, PAGE_SIZE / sizeof(struct location),
>> + GFP_KERNEL)) {
>> + seq_puts(seq, "Out of memory\n");
>> + return ERR_PTR(-ENOMEM);
>> + }
>> + /* Push back cpu slabs */
>> + flush_all(s);
>> +
>> + for_each_kmem_cache_node(s, node, n) {
>> + unsigned long flags;
>> + struct page *page;
>> +
>> + if (!atomic_long_read(&n->nr_slabs))
>> + continue;
>> +
>> + spin_lock_irqsave(&n->list_lock, flags);
>> + list_for_each_entry(page, &n->partial, slab_list)
>> + process_slab(&t, s, page, alloc);
>> + list_for_each_entry(page, &n->full, slab_list)
>> + process_slab(&t, s, page, alloc);
>> + spin_unlock_irqrestore(&n->list_lock, flags);
>> + }
>> + }
>> +
>> + if (*ppos < t.count) {
>> + *spos = *ppos;
>> + return spos;
>> + }
>> +
>> + kfree(spos);
>> + return NULL;
>> +}
>> +
>> +static const struct seq_operations slab_debugfs_sops = {
>> + .start = slab_debugfs_start,
>> + .next = slab_debugfs_next,
>> + .stop = slab_debugfs_stop,
>> + .show = slab_debugfs_show
>> +};
>> +DEFINE_SEQ_ATTRIBUTE(slab_debugfs);
>> +
>> +static void debugfs_slab_add(struct kmem_cache *s)
>> +{
>> + const char *name;
>> + int unmergeable = slab_unmergeable(s);
>> +
>> + if (unlikely(!slab_debugfs_root))
>> + return;
>> +
>> + if (!unmergeable && disable_higher_order_debug &&
>> + (slub_debug & DEBUG_METADATA_FLAGS))
>> + unmergeable = 1;
>> +
>> + if (unmergeable) {
>> + /*
>> + * Slabcache can never be merged so we can use the name proper.
>> + * This is typically the case for debug situations. In that
>> + * case we can catch duplicate names easily.
>> + */
>> + debugfs_remove_recursive(s->slab_cache_dentry);
>> + name = s->name;
>> + } else {
>> + /*
>> + * Create a unique name for the slab as a target
>> + * for the symlinks.
>> + */
>> + name = create_unique_id(s);
>> + }
>> +
>> + s->slab_cache_dentry = debugfs_create_dir(name, slab_debugfs_root);
>> + if (!IS_ERR(s->slab_cache_dentry)) {
>
> No need for you to care here either, just call debugfs and keep on
> going.
>
update in new patch,
https://lore.kernel.org/linux-mm/1621341949-26762-1-git-send-email-faiyazm@codeaurora.org/T/#u
>> + debugfs_create_file("alloc_traces", 0400,
>> + s->slab_cache_dentry, s, &slab_debugfs_fops);
>> +
>> + debugfs_create_file("free_traces", 0400,
>> + s->slab_cache_dentry, s, &slab_debugfs_fops);
>> + }
>> +
>> + if (!unmergeable) {
>> + /* Setup first alias */
>> + debugfs_slab_alias(s, s->name);
>> + }
>
> Do you really need the { }?
>
>> +}
>> +
>> +void debugfs_slab_release(struct kmem_cache *s)
>> +{
>> + if (slab_state >= FULL)
>> + debugfs_remove_recursive(s->slab_cache_dentry);
>
> Why does the state matter?
>
> And again, can't you just look up the debugfs dentry here?
>
>> +}
>> +
>> +static int __init slab_debugfs_init(void)
>> +{
>> + struct kmem_cache *s;
>> + int err;
>> +
>> + slab_debugfs_root = debugfs_create_dir("slab", NULL);
>> + if (!IS_ERR(slab_debugfs_root)) {
>> +
>> + slab_state = FULL;
>
> Again, no need to check.
>
>> +
>> + list_for_each_entry(s, &slab_caches, list)
>> + debugfs_slab_add(s);
>> + } else {
>> + pr_err("Cannot create slab debugfs.\n");
>> + return IS_ERR(slab_debugfs_root);
>> + }
>> +
>> + while (alias_list) {
>> + struct saved_alias *al = alias_list;
>> +
>> + alias_list = alias_list->next;
>> +
>> + err = debugfs_slab_alias(al->s, al->name);
>> + if (err)
>> + pr_err("SLUB: Unable to add boot slab alias %s to debugfs\n",
>> + al->name);
>
> Why does this matter?
>
updated in new patch,
https://lore.kernel.org/linux-mm/1621341949-26762-1-git-send-email-faiyazm@codeaurora.org/T/#u
>> + kfree(al);
>> + }
>> +
>> + return 0;
>
> See, you always return 0, no need to check the above stuff :)
>
> thanks,
>
> greg k-h
>
Thanks and regards,
Mohammed Faiyaz
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