mm: shrinkers: provide shrinkers with names

Currently shrinkers are anonymous objects.  For debugging purposes they
can be identified by count/scan function names, but it's not always
useful: e.g.  for superblock's shrinkers it's nice to have at least an
idea of to which superblock the shrinker belongs.

This commit adds names to shrinkers.  register_shrinker() and
prealloc_shrinker() functions are extended to take a format and arguments
to master a name.

In some cases it's not possible to determine a good name at the time when
a shrinker is allocated.  For such cases shrinker_debugfs_rename() is
provided.

The expected format is:
    <subsystem>-<shrinker_type>[:<instance>]-<id>
For some shrinkers an instance can be encoded as (MAJOR:MINOR) pair.

After this change the shrinker debugfs directory looks like:
  $ cd /sys/kernel/debug/shrinker/
  $ ls
    dquota-cache-16     sb-devpts-28     sb-proc-47       sb-tmpfs-42
    mm-shadow-18        sb-devtmpfs-5    sb-proc-48       sb-tmpfs-43
    mm-zspool:zram0-34  sb-hugetlbfs-17  sb-pstore-31     sb-tmpfs-44
    rcu-kfree-0         sb-hugetlbfs-33  sb-rootfs-2      sb-tmpfs-49
    sb-aio-20           sb-iomem-12      sb-securityfs-6  sb-tracefs-13
    sb-anon_inodefs-15  sb-mqueue-21     sb-selinuxfs-22  sb-xfs:vda1-36
    sb-bdev-3           sb-nsfs-4        sb-sockfs-8      sb-zsmalloc-19
    sb-bpf-32           sb-pipefs-14     sb-sysfs-26      thp-deferred_split-10
    sb-btrfs:vda2-24    sb-proc-25       sb-tmpfs-1       thp-zero-9
    sb-cgroup2-30       sb-proc-39       sb-tmpfs-27      xfs-buf:vda1-37
    sb-configfs-23      sb-proc-41       sb-tmpfs-29      xfs-inodegc:vda1-38
    sb-dax-11           sb-proc-45       sb-tmpfs-35
    sb-debugfs-7        sb-proc-46       sb-tmpfs-40

[roman.gushchin@linux.dev: fix build warnings]
  Link: https://lkml.kernel.org/r/Yr+ZTnLb9lJk6fJO@castle
  Reported-by: kernel test robot <lkp@intel.com>
Link: https://lkml.kernel.org/r/20220601032227.4076670-4-roman.gushchin@linux.dev
Signed-off-by: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Cc: Dave Chinner <dchinner@redhat.com>
Cc: Hillf Danton <hdanton@sina.com>
Cc: Kent Overstreet <kent.overstreet@gmail.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 55 insertions, 3 deletions

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 35dedff79eb4..97ac6c6c026d 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -608,7 +608,7 @@ static unsigned long lruvec_lru_size(struct lruvec *lruvec, enum lru_list lru,
 /*
  * Add a shrinker callback to be called from the vm.
  */
-int prealloc_shrinker(struct shrinker *shrinker)
+static int __prealloc_shrinker(struct shrinker *shrinker)
 {
 	unsigned int size;
 	int err;
@@ -632,8 +632,36 @@ int prealloc_shrinker(struct shrinker *shrinker)
 	return 0;
 }
 
+#ifdef CONFIG_SHRINKER_DEBUG
+int prealloc_shrinker(struct shrinker *shrinker, const char *fmt, ...)
+{
+	va_list ap;
+	int err;
+
+	va_start(ap, fmt);
+	shrinker->name = kvasprintf_const(GFP_KERNEL, fmt, ap);
+	va_end(ap);
+	if (!shrinker->name)
+		return -ENOMEM;
+
+	err = __prealloc_shrinker(shrinker);
+	if (err)
+		kfree_const(shrinker->name);
+
+	return err;
+}
+#else
+int prealloc_shrinker(struct shrinker *shrinker, const char *fmt, ...)
+{
+	return __prealloc_shrinker(shrinker);
+}
+#endif
+
 void free_prealloced_shrinker(struct shrinker *shrinker)
 {
+#ifdef CONFIG_SHRINKER_DEBUG
+	kfree_const(shrinker->name);
+#endif
 	if (shrinker->flags & SHRINKER_MEMCG_AWARE) {
 		down_write(&shrinker_rwsem);
 		unregister_memcg_shrinker(shrinker);
@@ -654,15 +682,39 @@ void register_shrinker_prepared(struct shrinker *shrinker)
 	up_write(&shrinker_rwsem);
 }
 
-int register_shrinker(struct shrinker *shrinker)
+static int __register_shrinker(struct shrinker *shrinker)
 {
-	int err = prealloc_shrinker(shrinker);
+	int err = __prealloc_shrinker(shrinker);
 
 	if (err)
 		return err;
 	register_shrinker_prepared(shrinker);
 	return 0;
 }
+
+#ifdef CONFIG_SHRINKER_DEBUG
+int register_shrinker(struct shrinker *shrinker, const char *fmt, ...)
+{
+	va_list ap;
+	int err;
+
+	va_start(ap, fmt);
+	shrinker->name = kvasprintf_const(GFP_KERNEL, fmt, ap);
+	va_end(ap);
+	if (!shrinker->name)
+		return -ENOMEM;
+
+	err = __register_shrinker(shrinker);
+	if (err)
+		kfree_const(shrinker->name);
+	return err;
+}
+#else
+int register_shrinker(struct shrinker *shrinker, const char *fmt, ...)
+{
+	return __register_shrinker(shrinker);
+}
+#endif
 EXPORT_SYMBOL(register_shrinker);
 
 /*