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authorRoman Gushchin <roman.gushchin@linux.dev>2022-05-31 20:22:23 -0700
committerakpm <akpm@linux-foundation.org>2022-07-03 18:08:40 -0700
commit5035ebc644aec92d55d1bbfe042f35341e4bffb5 (patch)
treeb6b76cac588da2cb4f7e17761fc8f508bef80051
parentc15187a4a2d660bf490f7873afd0de5288f65c8f (diff)
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mm: shrinkers: introduce debugfs interface for memory shrinkers
This commit introduces the /sys/kernel/debug/shrinker debugfs interface which provides an ability to observe the state of individual kernel memory shrinkers. Because the feature adds some memory overhead (which shouldn't be large unless there is a huge amount of registered shrinkers), it's guarded by a config option (enabled by default). This commit introduces the "count" interface for each shrinker registered in the system. The output is in the following format: <cgroup inode id> <nr of objects on node 0> <nr of objects on node 1>... <cgroup inode id> <nr of objects on node 0> <nr of objects on node 1>... ... To reduce the size of output on machines with many thousands cgroups, if the total number of objects on all nodes is 0, the line is omitted. If the shrinker is not memcg-aware or CONFIG_MEMCG is off, 0 is printed as cgroup inode id. If the shrinker is not numa-aware, 0's are printed for all nodes except the first one. This commit gives debugfs entries simple numeric names, which are not very convenient. The following commit in the series will provide shrinkers with more meaningful names. [akpm@linux-foundation.org: remove WARN_ON_ONCE(), per Roman] Reported-by: syzbot+300d27c79fe6d4cbcc39@syzkaller.appspotmail.com Link: https://lkml.kernel.org/r/20220601032227.4076670-3-roman.gushchin@linux.dev Signed-off-by: Roman Gushchin <roman.gushchin@linux.dev> Reviewed-by: Kent Overstreet <kent.overstreet@gmail.com> Acked-by: Muchun Song <songmuchun@bytedance.com> Cc: Christophe JAILLET <christophe.jaillet@wanadoo.fr> Cc: Dave Chinner <dchinner@redhat.com> Cc: Hillf Danton <hdanton@sina.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
-rw-r--r--include/linux/shrinker.h19
-rw-r--r--lib/Kconfig.debug9
-rw-r--r--mm/Makefile1
-rw-r--r--mm/shrinker_debug.c168
-rw-r--r--mm/vmscan.c6
5 files changed, 200 insertions, 3 deletions
diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h
index 76fbf92b04d9..2ced8149c513 100644
--- a/include/linux/shrinker.h
+++ b/include/linux/shrinker.h
@@ -73,6 +73,10 @@ struct shrinker {
/* ID in shrinker_idr */
int id;
#endif
+#ifdef CONFIG_SHRINKER_DEBUG
+ int debugfs_id;
+ struct dentry *debugfs_entry;
+#endif
/* objs pending delete, per node */
atomic_long_t *nr_deferred;
};
@@ -94,4 +98,17 @@ extern int register_shrinker(struct shrinker *shrinker);
extern void unregister_shrinker(struct shrinker *shrinker);
extern void free_prealloced_shrinker(struct shrinker *shrinker);
extern void synchronize_shrinkers(void);
-#endif
+
+#ifdef CONFIG_SHRINKER_DEBUG
+extern int shrinker_debugfs_add(struct shrinker *shrinker);
+extern void shrinker_debugfs_remove(struct shrinker *shrinker);
+#else /* CONFIG_SHRINKER_DEBUG */
+static inline int shrinker_debugfs_add(struct shrinker *shrinker)
+{
+ return 0;
+}
+static inline void shrinker_debugfs_remove(struct shrinker *shrinker)
+{
+}
+#endif /* CONFIG_SHRINKER_DEBUG */
+#endif /* _LINUX_SHRINKER_H */
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 2e24db4bff19..0b483a8da409 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -699,6 +699,15 @@ config DEBUG_OBJECTS_ENABLE_DEFAULT
help
Debug objects boot parameter default value
+config SHRINKER_DEBUG
+ default y
+ bool "Enable shrinker debugging support"
+ depends on DEBUG_FS
+ help
+ Say Y to enable the shrinker debugfs interface which provides
+ visibility into the kernel memory shrinkers subsystem.
+ Disable it to avoid an extra memory footprint.
+
config HAVE_DEBUG_KMEMLEAK
bool
diff --git a/mm/Makefile b/mm/Makefile
index 6f9ffa968a1a..9a564f836403 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -133,3 +133,4 @@ obj-$(CONFIG_PAGE_REPORTING) += page_reporting.o
obj-$(CONFIG_IO_MAPPING) += io-mapping.o
obj-$(CONFIG_HAVE_BOOTMEM_INFO_NODE) += bootmem_info.o
obj-$(CONFIG_GENERIC_IOREMAP) += ioremap.o
+obj-$(CONFIG_SHRINKER_DEBUG) += shrinker_debug.o
diff --git a/mm/shrinker_debug.c b/mm/shrinker_debug.c
new file mode 100644
index 000000000000..1a70556bd46c
--- /dev/null
+++ b/mm/shrinker_debug.c
@@ -0,0 +1,168 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/idr.h>
+#include <linux/slab.h>
+#include <linux/debugfs.h>
+#include <linux/seq_file.h>
+#include <linux/shrinker.h>
+#include <linux/memcontrol.h>
+
+/* defined in vmscan.c */
+extern struct rw_semaphore shrinker_rwsem;
+extern struct list_head shrinker_list;
+
+static DEFINE_IDA(shrinker_debugfs_ida);
+static struct dentry *shrinker_debugfs_root;
+
+static unsigned long shrinker_count_objects(struct shrinker *shrinker,
+ struct mem_cgroup *memcg,
+ unsigned long *count_per_node)
+{
+ unsigned long nr, total = 0;
+ int nid;
+
+ for_each_node(nid) {
+ if (nid == 0 || (shrinker->flags & SHRINKER_NUMA_AWARE)) {
+ struct shrink_control sc = {
+ .gfp_mask = GFP_KERNEL,
+ .nid = nid,
+ .memcg = memcg,
+ };
+
+ nr = shrinker->count_objects(shrinker, &sc);
+ if (nr == SHRINK_EMPTY)
+ nr = 0;
+ } else {
+ nr = 0;
+ }
+
+ count_per_node[nid] = nr;
+ total += nr;
+ }
+
+ return total;
+}
+
+static int shrinker_debugfs_count_show(struct seq_file *m, void *v)
+{
+ struct shrinker *shrinker = m->private;
+ unsigned long *count_per_node;
+ struct mem_cgroup *memcg;
+ unsigned long total;
+ bool memcg_aware;
+ int ret, nid;
+
+ count_per_node = kcalloc(nr_node_ids, sizeof(unsigned long), GFP_KERNEL);
+ if (!count_per_node)
+ return -ENOMEM;
+
+ ret = down_read_killable(&shrinker_rwsem);
+ if (ret) {
+ kfree(count_per_node);
+ return ret;
+ }
+ rcu_read_lock();
+
+ memcg_aware = shrinker->flags & SHRINKER_MEMCG_AWARE;
+
+ memcg = mem_cgroup_iter(NULL, NULL, NULL);
+ do {
+ if (memcg && !mem_cgroup_online(memcg))
+ continue;
+
+ total = shrinker_count_objects(shrinker,
+ memcg_aware ? memcg : NULL,
+ count_per_node);
+ if (total) {
+ seq_printf(m, "%lu", mem_cgroup_ino(memcg));
+ for_each_node(nid)
+ seq_printf(m, " %lu", count_per_node[nid]);
+ seq_putc(m, '\n');
+ }
+
+ if (!memcg_aware) {
+ mem_cgroup_iter_break(NULL, memcg);
+ break;
+ }
+
+ if (signal_pending(current)) {
+ mem_cgroup_iter_break(NULL, memcg);
+ ret = -EINTR;
+ break;
+ }
+ } while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL);
+
+ rcu_read_unlock();
+ up_read(&shrinker_rwsem);
+
+ kfree(count_per_node);
+ return ret;
+}
+DEFINE_SHOW_ATTRIBUTE(shrinker_debugfs_count);
+
+int shrinker_debugfs_add(struct shrinker *shrinker)
+{
+ struct dentry *entry;
+ char buf[16];
+ int id;
+
+ lockdep_assert_held(&shrinker_rwsem);
+
+ /* debugfs isn't initialized yet, add debugfs entries later. */
+ if (!shrinker_debugfs_root)
+ return 0;
+
+ id = ida_alloc(&shrinker_debugfs_ida, GFP_KERNEL);
+ if (id < 0)
+ return id;
+ shrinker->debugfs_id = id;
+
+ snprintf(buf, sizeof(buf), "%d", id);
+
+ /* create debugfs entry */
+ entry = debugfs_create_dir(buf, shrinker_debugfs_root);
+ if (IS_ERR(entry)) {
+ ida_free(&shrinker_debugfs_ida, id);
+ return PTR_ERR(entry);
+ }
+ shrinker->debugfs_entry = entry;
+
+ debugfs_create_file("count", 0220, entry, shrinker,
+ &shrinker_debugfs_count_fops);
+ return 0;
+}
+
+void shrinker_debugfs_remove(struct shrinker *shrinker)
+{
+ lockdep_assert_held(&shrinker_rwsem);
+
+ if (!shrinker->debugfs_entry)
+ return;
+
+ debugfs_remove_recursive(shrinker->debugfs_entry);
+ ida_free(&shrinker_debugfs_ida, shrinker->debugfs_id);
+}
+
+static int __init shrinker_debugfs_init(void)
+{
+ struct shrinker *shrinker;
+ struct dentry *dentry;
+ int ret = 0;
+
+ dentry = debugfs_create_dir("shrinker", NULL);
+ if (IS_ERR(dentry))
+ return PTR_ERR(dentry);
+ shrinker_debugfs_root = dentry;
+
+ /* Create debugfs entries for shrinkers registered at boot */
+ down_write(&shrinker_rwsem);
+ list_for_each_entry(shrinker, &shrinker_list, list)
+ if (!shrinker->debugfs_entry) {
+ ret = shrinker_debugfs_add(shrinker);
+ if (ret)
+ break;
+ }
+ up_write(&shrinker_rwsem);
+
+ return ret;
+}
+late_initcall(shrinker_debugfs_init);
diff --git a/mm/vmscan.c b/mm/vmscan.c
index f7d9a683e3a7..35dedff79eb4 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -190,8 +190,8 @@ static void set_task_reclaim_state(struct task_struct *task,
task->reclaim_state = rs;
}
-static LIST_HEAD(shrinker_list);
-static DECLARE_RWSEM(shrinker_rwsem);
+LIST_HEAD(shrinker_list);
+DECLARE_RWSEM(shrinker_rwsem);
#ifdef CONFIG_MEMCG
static int shrinker_nr_max;
@@ -650,6 +650,7 @@ void register_shrinker_prepared(struct shrinker *shrinker)
down_write(&shrinker_rwsem);
list_add_tail(&shrinker->list, &shrinker_list);
shrinker->flags |= SHRINKER_REGISTERED;
+ shrinker_debugfs_add(shrinker);
up_write(&shrinker_rwsem);
}
@@ -677,6 +678,7 @@ void unregister_shrinker(struct shrinker *shrinker)
shrinker->flags &= ~SHRINKER_REGISTERED;
if (shrinker->flags & SHRINKER_MEMCG_AWARE)
unregister_memcg_shrinker(shrinker);
+ shrinker_debugfs_remove(shrinker);
up_write(&shrinker_rwsem);
kfree(shrinker->nr_deferred);