[PATCH v6 3/9] fs: add percpu counters for significant multigrain timestamp events

Jeff Layton
2024-07-15T12:49:19Z

Four percpu counters for counting various stats around mgtimes, and a
new debugfs file for displaying them:

- number of attempted ctime updates
- number of successful i_ctime_nsec swaps
- number of fine-grained timestamp fetches
- number of floor value swaps

Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
fs/inode.c | 70 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 69 insertions(+), 1 deletion(-)

diff --git a/fs/inode.c b/fs/inode.c
index 869994285e87..fff844345c35 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -21,6 +21,8 @@
#include <linux/list_lru.h>
#include <linux/iversion.h>
#include <linux/rw_hint.h>
+#include <linux/seq_file.h>
+#include <linux/debugfs.h>
#include <trace/events/writeback.h>
#define CREATE_TRACE_POINTS
#include <trace/events/timestamp.h>
@@ -80,6 +82,10 @@ EXPORT_SYMBOL(empty_aops);

static DEFINE_PER_CPU(unsigned long, nr_inodes);
static DEFINE_PER_CPU(unsigned long, nr_unused);
+static DEFINE_PER_CPU(unsigned long, mg_ctime_updates);
+static DEFINE_PER_CPU(unsigned long, mg_fine_stamps);
+static DEFINE_PER_CPU(unsigned long, mg_floor_swaps);
+static DEFINE_PER_CPU(unsigned long, mg_ctime_swaps);

static struct kmem_cache *inode_cachep __ro_after_init;

@@ -101,6 +107,42 @@ static inline long get_nr_inodes_unused(void)
return sum < 0 ? 0 : sum;
}

+static long get_mg_ctime_updates(void)
+{
+ int i;
+ long sum = 0;
+ for_each_possible_cpu(i)
+ sum += per_cpu(mg_ctime_updates, i);
+ return sum < 0 ? 0 : sum;
+}
+
+static long get_mg_fine_stamps(void)
+{
+ int i;
+ long sum = 0;
+ for_each_possible_cpu(i)
+ sum += per_cpu(mg_fine_stamps, i);
+ return sum < 0 ? 0 : sum;
+}
+
+static long get_mg_floor_swaps(void)
+{
+ int i;
+ long sum = 0;
+ for_each_possible_cpu(i)
+ sum += per_cpu(mg_floor_swaps, i);
+ return sum < 0 ? 0 : sum;
+}
+
+static long get_mg_ctime_swaps(void)
+{
+ int i;
+ long sum = 0;
+ for_each_possible_cpu(i)
+ sum += per_cpu(mg_ctime_swaps, i);
+ return sum < 0 ? 0 : sum;
+}
+
long get_nr_dirty_inodes(void)
{
/* not actually dirty inodes, but a wild approximation */
@@ -2655,6 +2697,7 @@ struct timespec64 inode_set_ctime_current(struct inode *inode)

/* Get a fine-grained time */
fine = ktime_get();
+ this_cpu_inc(mg_fine_stamps);

/*
* If the cmpxchg works, we take the new floor value. If
@@ -2663,11 +2706,14 @@ struct timespec64 inode_set_ctime_current(struct inode *inode)
* as good, so keep it.
*/
old = floor;
- if (!atomic64_try_cmpxchg(&ctime_floor, &old, fine))
+ if (atomic64_try_cmpxchg(&ctime_floor, &old, fine))
+ this_cpu_inc(mg_floor_swaps);
+ else
fine = old;
now = ktime_mono_to_real(fine);
}
}
+ this_cpu_inc(mg_ctime_updates);
now_ts = timestamp_truncate(ktime_to_timespec64(now), inode);
cur = cns;

@@ -2682,6 +2728,7 @@ struct timespec64 inode_set_ctime_current(struct inode *inode)
/* If swap occurred, then we're (mostly) done */
inode->i_ctime_sec = now_ts.tv_sec;
trace_ctime_ns_xchg(inode, cns, now_ts.tv_nsec, cur);
+ this_cpu_inc(mg_ctime_swaps);
} else {
/*
* Was the change due to someone marking the old ctime QUERIED?
@@ -2751,3 +2798,24 @@ umode_t mode_strip_sgid(struct mnt_idmap *idmap,
return mode & ~S_ISGID;
}
EXPORT_SYMBOL(mode_strip_sgid);
+
+static int mgts_show(struct seq_file *s, void *p)
+{
+ long ctime_updates = get_mg_ctime_updates();
+ long ctime_swaps = get_mg_ctime_swaps();
+ long fine_stamps = get_mg_fine_stamps();
+ long floor_swaps = get_mg_floor_swaps();
+
+ seq_printf(s, "%lu %lu %lu %lu\n",
+ ctime_updates, ctime_swaps, fine_stamps, floor_swaps);
+ return 0;
+}
+
+DEFINE_SHOW_ATTRIBUTE(mgts);
+
+static int __init mg_debugfs_init(void)
+{
+ debugfs_create_file("multigrain_timestamps", S_IFREG | S_IRUGO, NULL, NULL, &mgts_fops);
+ return 0;
+}
+late_initcall(mg_debugfs_init);

--
2.45.2