On 5/26/2021 5:08 PM, Vlastimil Babka wrote:

On 5/25/21 9:38 AM, Faiyaz Mohammed wrote:

quoted

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.

Reported-by: kernel test robot <redacted>
Reported-by: Dan Carpenter <redacted>

These were IIRC bot reports for some bugs in the previous versions, so keeping
the Reported-by: for the whole patch is misleading - these were not reports for
the sysfs issues this patch fixes by moving the files to debugfs.

Yes, I will update in next patch version.

quoted

Signed-off-by: Faiyaz Mohammed <redacted>
---
changes in V7:
        - Drop the older alloc_calls and free_calls interface.
changes in v6:
        - https://lore.kernel.org/linux-mm/1621341949-26762-1-git-send-email-faiyazm@codeaurora.org/ (local)

changes in v5:
        - https://lore.kernel.org/linux-mm/1620296523-21922-1-git-send-email-faiyazm@codeaurora.org/ (local)

changes in v4:
        - https://lore.kernel.org/linux-mm/1618583239-18124-1-git-send-email-faiyazm@codeaurora.org/ (local)

changes in v3:
        - https://lore.kernel.org/linux-mm/1617712064-12264-1-git-send-email-faiyazm@codeaurora.org/ (local)

changes in v2:
        - https://lore.kernel.org/linux-mm/3ac1d3e6-6207-96ad-16a1-0f5139d8b2b5@codeaurora.org/ (local)

changes in v1:
        - https://lore.kernel.org/linux-mm/1610443287-23933-1-git-send-email-faiyazm@codeaurora.org/ (local)

 include/linux/slub_def.h |   8 ++
 mm/slab_common.c         |   9 ++
 mm/slub.c                | 353 ++++++++++++++++++++++++++++++++++-------------
 3 files changed, 276 insertions(+), 94 deletions(-)

I don't see any of the symlinks under /sys/kernel/debug/slab/, so I think the
aliases handling code is wrong, and I can see at least two reasons why it could be:

I think I missed one thing, when CONFIG_SLUB_DEBUG_ON enable or
slub_debug is pass through command line __kmem_cache_alias() will return
null, so no symlinks will be created even if CONFIG_SLAB_MERGE_DEFAULT
is enable and to store user data we need to enable CONFIG_SLUB_DEBUG_ON
or pass slub_debug through command line.

quoted

@@ -4525,6 +4535,8 @@ __kmem_cache_alias(const char *name, unsigned int size, unsigned int align,
 			s->refcount--;
 			s = NULL;
 		}
+
+		debugfs_slab_alias(s, name);

Here you might be calling debugfs_slab_alias() with NULL if the
sysfs_slab_alias() above returned true.

I think we can drop debugfs_slab_alias implementation.

quoted

 	}
 
 	return s;

...

quoted

+static int __init slab_debugfs_init(void)
+{
+	struct kmem_cache *s;
+
+	slab_debugfs_root = debugfs_create_dir("slab", NULL);
+
+	slab_state = FULL;
+
+	list_for_each_entry(s, &slab_caches, list)
+		debugfs_slab_add(s);
+
+	while (alias_list) {
+		struct saved_alias *al = alias_list;

alias_list a single list and both slab_sysfs_init() and slab_debugfs_init()
flush it. So only the init call that happens to be called first, does actually
find an unflushed list. I think you
need to use a separate list for debugfs (simpler) or a shared list with both
sysfs and debugfs processing (probably more complicated).

same here, I think we can drop the debugfs alias change.

And finally a question, perhaps also for Greg. With sysfs, we hand out the
lifecycle of struct kmem_cache to sysfs, to ensure we are not reading sysfs
files of a cache that has been removed.

But with debugfs, what are the guarantees that things won't blow up when a
debugfs file is being read while somebody calls kmem_cache_destroy() on the cache?

quoted

+
+		alias_list = alias_list->next;
+
+		debugfs_slab_alias(al->s, al->name);
+
+		kfree(al);
+	}
+
+	return 0;
+
+}
+__initcall(slab_debugfs_init);
+#endif
 /*
  * The /proc/slabinfo ABI
  */