Re: [PATCH v9] mm: slub: move sysfs slab alloc/free interfaces to debugfs
From: Faiyaz Mohammed
Date: Sun Jun 06 2021 - 11:40:55 EST
On 6/3/2021 6:32 PM, Vlastimil Babka wrote:
> On 6/3/21 1:48 PM, 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.
>>
>> Debugfs cache will be created if SLAB_STORE_USER flag is set.
>>
>> Rename the alloc_calls/free_calls to alloc_traces/free_traces,
>> to be inline with what it does.
>>
>> Signed-off-by: Faiyaz Mohammed <faiyazm@xxxxxxxxxxxxxx>
>> ---
>> changes in v9:
>> - Move the debugfs_slab_release to mm/slab.h.
>> - Remove the global loc_track variable and using seq_file private.
>>
>> changes in v8:
>> - https://lore.kernel.org/linux-mm/1622542057-14632-1-git-send-email-faiyazm@xxxxxxxxxxxxxx/
>>
>> changes in V7:
>> - https://lore.kernel.org/linux-mm/1621928285-751-1-git-send-email-faiyazm@xxxxxxxxxxxxxx/
>>
>> changes in v6:
>> - https://lore.kernel.org/linux-mm/1621341949-26762-1-git-send-email-faiyazm@xxxxxxxxxxxxxx/
>>
>> changes in v5:
>> - https://lore.kernel.org/linux-mm/1620296523-21922-1-git-send-email-faiyazm@xxxxxxxxxxxxxx/
>>
>> changes in v4:
>> - https://lore.kernel.org/linux-mm/1618583239-18124-1-git-send-email-faiyazm@xxxxxxxxxxxxxx/
>>
>> changes in v3:
>> - https://lore.kernel.org/linux-mm/1617712064-12264-1-git-send-email-faiyazm@xxxxxxxxxxxxxx/
>>
>> changes in v2:
>> - https://lore.kernel.org/linux-mm/3ac1d3e6-6207-96ad-16a1-0f5139d8b2b5@xxxxxxxxxxxxxx/
>>
>> changes in v1
>> - https://lore.kernel.org/linux-mm/1610443287-23933-1-git-send-email-faiyazm@xxxxxxxxxxxxxx/
>>
>> mm/slab.h | 8 ++
>> mm/slab_common.c | 2 +
>> mm/slub.c | 312 ++++++++++++++++++++++++++++++++++++++-----------------
>> 3 files changed, 229 insertions(+), 93 deletions(-)
>>
>> diff --git a/mm/slab.h b/mm/slab.h
>> index 18c1927..3b60925 100644
>> --- a/mm/slab.h
>> +++ b/mm/slab.h
>> @@ -630,6 +630,14 @@ static inline bool slab_want_init_on_free(struct kmem_cache *c)
>> return false;
>> }
>>
>> +#if defined(CONFIG_DEBUG_FS) && defined(CONFIG_SLUB_DEBUG)
>> +void debugfs_slab_release(struct kmem_cache *);
>> +#else
>> +static inline void debugfs_slab_release(struct kmem_cache *s)
>> +{
>> +}
>> +#endif
>> +
>> #ifdef CONFIG_PRINTK
>> #define KS_ADDRS_COUNT 16
>> struct kmem_obj_info {
>> diff --git a/mm/slab_common.c b/mm/slab_common.c
>> index a4a5714..bca69b6 100644
>> --- a/mm/slab_common.c
>> +++ b/mm/slab_common.c
>> @@ -469,6 +469,7 @@ static int shutdown_cache(struct kmem_cache *s)
>> list_del(&s->list);
>>
>> if (s->flags & SLAB_TYPESAFE_BY_RCU) {
>> + debugfs_slab_release(s);
>> #ifdef SLAB_SUPPORTS_SYSFS
>> sysfs_slab_unlink(s);
>> #endif
>> @@ -476,6 +477,7 @@ static int shutdown_cache(struct kmem_cache *s)
>> schedule_work(&slab_caches_to_rcu_destroy_work);
>> } else {
>> kfence_shutdown_cache(s);
>> + debugfs_slab_release(s);
>> #ifdef SLAB_SUPPORTS_SYSFS
>> sysfs_slab_unlink(s);
>> sysfs_slab_release(s);
>> diff --git a/mm/slub.c b/mm/slub.c
>> index 3f96e09..c00c9d5 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 +226,12 @@ static inline int sysfs_slab_alias(struct kmem_cache *s, const char *p)
>> { return 0; }
>> #endif
>>
>> +#if defined(CONFIG_DEBUG_FS) && defined(CONFIG_SLUB_DEBUG)
>> +static void debugfs_slab_add(struct kmem_cache *);
>> +#else
>> +static inline void debugfs_slab_add(struct kmem_cache *s) { }
>> +#endif
>> +
>> static inline void stat(const struct kmem_cache *s, enum stat_item si)
>> {
>> #ifdef CONFIG_SLUB_STATS
>> @@ -4546,6 +4553,9 @@ int __kmem_cache_create(struct kmem_cache *s, slab_flags_t flags)
>> if (err)
>> __kmem_cache_release(s);
>>
>> + if (s->flags & SLAB_STORE_USER)
>> + debugfs_slab_add(s);
>> +
>> return err;
>> }
>>
>> @@ -4686,6 +4696,8 @@ 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.
>> @@ -4709,6 +4721,8 @@ struct loc_track {
>> struct location *loc;
>> };
>>
>> +static struct dentry *slab_debugfs_root;
>> +
>> static void free_loc_track(struct loc_track *t)
>> {
>> if (t->max)
>> @@ -4825,82 +4839,7 @@ 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
>> @@ -5350,21 +5289,6 @@ static ssize_t validate_store(struct kmem_cache *s,
>> }
>> 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);
>> -}
>> -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);
>> -}
>> -SLAB_ATTR_RO(free_calls);
>> #endif /* CONFIG_SLUB_DEBUG */
>>
>> #ifdef CONFIG_FAILSLAB
>> @@ -5528,8 +5452,6 @@ static struct attribute *slab_attrs[] = {
>> &poison_attr.attr,
>> &store_user_attr.attr,
>> &validate_attr.attr,
>> - &alloc_calls_attr.attr,
>> - &free_calls_attr.attr,
>> #endif
>> #ifdef CONFIG_ZONE_DMA
>> &cache_dma_attr.attr,
>> @@ -5818,6 +5740,210 @@ 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 slab_debugfs_show(struct seq_file *seq, void *v)
>> +{
>> +
>> + struct location *l;
>> + unsigned int idx = *(unsigned int *)v;
>> + struct loc_track *t = seq->private;
>> +
>> + 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)
>> + seq_puts(seq, "No data\n");
>> +
>> + return 0;
>> +}
>> +
>> +static void slab_debugfs_stop(struct seq_file *seq, void *v)
>> +{
>> + if ((!v) &&
>> + ((struct loc_track *)seq->private)->count == (seq->index - 1))
>> + free_loc_track((struct loc_track *)seq->private);
>
> Please use a local "loc_track *t" variable as elsewhere to avoid these multiple
> inline casts.
>
Okay, will update in next patch version.
> I don't think this code ever executes anything as !v is most likely never true?
>
It will execute when slab_debugfs_next() return NULL (v will be NULL)
and slab_debugfs_next() will return NULLL, when it will completed the
t->count reading. Still, I will update in next patch version.
> Also I don't understand why the count == seq->index - 1 comparison.
>
The count == seq->index - 1 comparision is to avoid the calling of
free_loc_track() multiple time. Still, I will update in next patch version.
> I think this function should do simply:
>
> kfree(v);
>
hmm, yes we can do that but when ever seq_has_overflowed() happen it
will call the ->stop(), so to avoiding that returning NULL from
slab_debugfs_next() and doing !v check in slab_debugfs_stop. Still, I
will update in next patch version.
> More on the loc_track and seq->private lifecycle below.
>
>> +}
>> +
>> +static void *slab_debugfs_next(struct seq_file *seq, void *v, loff_t *ppos)
>> +{
>> + loff_t *spos = v;
>> + struct loc_track *t = seq->private;
>> +
>> + if (*ppos < t->count) {
>> + *spos = *spos + 1;
>> + *ppos = *spos;
>> + return spos;
>> + }
>> +
>> + *spos = *spos + 1;
>> + *ppos = *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 (*ppos == 0) {
>
> Hm I think it's wrong to put all this behind the *ppos = 0 condition. Somebody
> might open the file, then do a lseek() and then read. The condition should be
> "did we fill lock_track info yet?".
>>> + if (strcmp(seq->file->f_path.dentry->d_name.name, "alloc_traces")
== 0)
>> + alloc = TRACK_ALLOC;
>> + else
>> + alloc = TRACK_FREE;
>> +
>> + seq->private = kmalloc(sizeof(struct loc_track), GFP_KERNEL);
>
> This should be better allocated during open().
>
>> + memset(seq->private, 0, sizeof(struct loc_track));
>> +
>> + if (!alloc_loc_track((struct loc_track *)seq->private,
>
> Again, please define a local variable for this at the top of the function.
> >> + PAGE_SIZE / sizeof(struct location), GFP_KERNEL)) {
>> + seq_puts(seq, "Out of memory\n");
>
> Hmm I don't think we can should to seq from a .start function.
> Maybe just return the -ENOMEM.
> >> + kfree(spos);
>> + 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((struct loc_track *)seq->private, s, page, alloc);
>> + list_for_each_entry(page, &n->full, slab_list)
>> + process_slab((struct loc_track *)seq->private, s, page, alloc);
>> + spin_unlock_irqrestore(&n->list_lock, flags);
>> + }
>> + }
>> +
>> + if (seq->private) {
>> + struct loc_track *t = seq->private;
>> +
>> + if (*ppos < t->count) {
>> + *spos = *ppos;
>> + return spos;
>> + }
>> + }
>> +
>> + kfree(spos);
>> + kfree(seq->private);
>> + 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
>> +};
>
> So I think the seq->private lifecycle should be tied to open()/close(), not
> start()/stop() where the latter is AFAIK performed as part of each read() syscall.
>
> So like in
> https://lore.kernel.org/linux-mm/20210521121127.24653-3-glittao@xxxxxxxxx/
> we'll need a "struct file_operations" too, with an .open function that
> __seq_open_private() to allocate seq->private and then do the initial
> alloc_loc_track().
>
> Then we'll also need a .release function that does free_loc_track() and then
> seq_release_private().
>
> The filling of loc_track with data could happen either in open() or in start(),
> but only once after open() and not depending on *ppos == 0 (as I mentioned above).
>
> The next/stop should take care only of the spos object.
>
>> +DEFINE_SEQ_ATTRIBUTE(slab_debugfs);
>> +
>> +static void debugfs_slab_add(struct kmem_cache *s)
>> +{
>> + const char *name;
>> + struct dentry *slab_cache_dir;
>> + 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.
>> + */
>> + slab_cache_dir = debugfs_lookup(s->name, slab_debugfs_root);
>> + debugfs_remove_recursive(slab_cache_dir);
>> + name = s->name;
>> + } else {
>> + /*
>> + * Create a unique name for the slab as a target
>> + * for the symlinks.
>> + */
>> + name = create_unique_id(s);
>> + }
>
> I think here we can rely on the fact that SLAB_STORE_USER cache will return
> slab_unmergeable(s) as 1, and greatly simplify the code above.
>
>> + slab_cache_dir = debugfs_create_dir(name, slab_debugfs_root);
>> +
>> + debugfs_create_file("alloc_traces", 0400,
>> + slab_cache_dir, s, &slab_debugfs_fops);
>> +
>> + debugfs_create_file("free_traces", 0400,
>> + slab_cache_dir, s, &slab_debugfs_fops);
>> +}
>> +
>> +void debugfs_slab_release(struct kmem_cache *s)
>> +{
>> + debugfs_remove_recursive(debugfs_lookup(s->name,
>> + slab_debugfs_root));
>> +}
>> +
>> +static int __init slab_debugfs_init(void)
>> +{
>> + struct kmem_cache *s;
>> +
>> + slab_debugfs_root = debugfs_create_dir("slab", NULL);
>> +
>> + list_for_each_entry(s, &slab_caches, list)
>> + if (s->flags & SLAB_STORE_USER)
>> + debugfs_slab_add(s);
>> +
>> + return 0;
>> +
>> +}
>> +__initcall(slab_debugfs_init);
>> +#endif
>> /*
>> * The /proc/slabinfo ABI
>> */
>>
>
I will update in next patch version.