Re: [PATCH v9] mm: slub: move sysfs slab alloc/free interfaces to debugfs
From: Vlastimil Babka
Date: Thu Jun 03 2021 - 09:03:04 EST
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.
I don't think this code ever executes anything as !v is most likely never true?
Also I don't understand why the count == seq->index - 1 comparison.
I think this function should do simply:
kfree(v);
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
> */
>