active_journal_entries is used to show the value of
fifo_used(&c->journal.pin)
fifo_used(&c->journal.pin) may count none-0-valued pins and 0-valued
pins both. While none-0 valued pins stands for active journal entries,
0-valued pins do not.
journal_reclaim() is used to pop out the 0-valued pins in the front
part of FIFO, and is called for each bch_journal() call.
There are 2 small cases which journal_reclaim() may not cover:
* The pin used in bch_journal_meta(): if no more IOs, then no reclaim.
If the pin is decreased to 0 in bch_journal_meta(), 0-valued pin is
kept and counted by fifo_used().
* When the system reboot up or the bcache module reload,
bch_journal_mark() will take up some pins, e.g N pins, for entries
to be replayed, and bch_journal_replay() will decrease the pins to 0.
If no new IOs after bcache up, active_journal_entries will keep N+1
(the 1 is set by bch_journal_next(), which is called() after
bch_journal_mark() in run_cache_set())
In both cases, active_journal_entries do not reflect the real active
entries. This does not impact the work of bcache subsystem, but may
introduce some confusion.
This patch will try to pop out the 0-valued pins in the front part of
journal.pin FIFO before show the realtime active journal entries.
Signed-off-by: Shenghui Wang <shhuiw@xxxxxxxxxxx>
---
drivers/md/bcache/sysfs.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)
diff --git a/drivers/md/bcache/sysfs.c b/drivers/md/bcache/sysfs.c
index 557a8a3270a1..a9b851bc5c98 100644
--- a/drivers/md/bcache/sysfs.c
+++ b/drivers/md/bcache/sysfs.c
@@ -692,7 +692,6 @@ SHOW(__bch_cache_set)
sysfs_print(cutoff_writeback, bch_cutoff_writeback);
sysfs_print(cutoff_writeback_sync, bch_cutoff_writeback_sync);
- sysfs_print(active_journal_entries, fifo_used(&c->journal.pin));
sysfs_printf(verify, "%i", c->verify);
sysfs_printf(key_merging_disabled, "%i", c->key_merging_disabled);
sysfs_printf(expensive_debug_checks,
@@ -704,6 +703,16 @@ SHOW(__bch_cache_set)
sysfs_printf(io_disable, "%i",
test_bit(CACHE_SET_IO_DISABLE, &c->flags));
+ if (attr == &sysfs_active_journal_entries) {
+ atomic_t p;
+
+ spin_lock(&c->journal.lock);
+ while (!atomic_read(&fifo_front(&c->journal.pin)))
+ fifo_pop(&c->journal.pin, p);
+ spin_unlock(&c->journal.lock);
+ return snprint(buf, PAGE_SIZE, fifo_used(&c->journal.pin));
+ }
+
if (attr == &sysfs_bset_tree_stats)
return bch_bset_print_stats(c, buf);
--
2.20.1
