[PATCH v2 3/6] writeback: support retrieving per group debug writeback stats of bdi
From: Kemeng Shi
Date: Wed Mar 27 2024 - 03:02:10 EST
Add /sys/kernel/debug/bdi/xxx/wb_stats to show per group writeback stats
of bdi.
Following domain hierarchy is tested:
global domain (320G)
/ \
cgroup domain1(10G) cgroup domain2(10G)
| |
bdi wb1 wb2
/* per wb writeback info of bdi is collected */
cat /sys/kernel/debug/bdi/252:16/wb_stats
WbCgIno: 1
WbWriteback: 0 kB
WbReclaimable: 0 kB
WbDirtyThresh: 0 kB
WbDirtied: 0 kB
WbWritten: 0 kB
WbWriteBandwidth: 102400 kBps
b_dirty: 0
b_io: 0
b_more_io: 0
b_dirty_time: 0
state: 1
WbCgIno: 4094
WbWriteback: 54432 kB
WbReclaimable: 766080 kB
WbDirtyThresh: 3094760 kB
WbDirtied: 1656480 kB
WbWritten: 837088 kB
WbWriteBandwidth: 132772 kBps
b_dirty: 1
b_io: 1
b_more_io: 0
b_dirty_time: 0
state: 7
WbCgIno: 4135
WbWriteback: 15232 kB
WbReclaimable: 786688 kB
WbDirtyThresh: 2909984 kB
WbDirtied: 1482656 kB
WbWritten: 681408 kB
WbWriteBandwidth: 124848 kBps
b_dirty: 0
b_io: 1
b_more_io: 0
b_dirty_time: 0
state: 7
Signed-off-by: Kemeng Shi <shikemeng@xxxxxxxxxxxxxxx>
---
include/linux/writeback.h | 1 +
mm/backing-dev.c | 88 +++++++++++++++++++++++++++++++++++++++
mm/page-writeback.c | 19 +++++++++
3 files changed, 108 insertions(+)
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index 9845cb62e40b..112d806ddbe4 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -355,6 +355,7 @@ int dirtytime_interval_handler(struct ctl_table *table, int write,
void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty);
unsigned long wb_calc_thresh(struct bdi_writeback *wb, unsigned long thresh);
+unsigned long cgwb_calc_thresh(struct bdi_writeback *wb);
void wb_update_bandwidth(struct bdi_writeback *wb);
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 8daf950e6855..e3953db7d88d 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -103,6 +103,91 @@ static void collect_wb_stats(struct wb_stats *stats,
}
#ifdef CONFIG_CGROUP_WRITEBACK
+static void wb_stats_show(struct seq_file *m, struct bdi_writeback *wb,
+ struct wb_stats *stats)
+{
+
+ seq_printf(m,
+ "WbCgIno: %10lu\n"
+ "WbWriteback: %10lu kB\n"
+ "WbReclaimable: %10lu kB\n"
+ "WbDirtyThresh: %10lu kB\n"
+ "WbDirtied: %10lu kB\n"
+ "WbWritten: %10lu kB\n"
+ "WbWriteBandwidth: %10lu kBps\n"
+ "b_dirty: %10lu\n"
+ "b_io: %10lu\n"
+ "b_more_io: %10lu\n"
+ "b_dirty_time: %10lu\n"
+ "state: %10lx\n",
+ cgroup_ino(wb->memcg_css->cgroup),
+ K(stats->nr_writeback),
+ K(stats->nr_reclaimable),
+ K(stats->wb_thresh),
+ K(stats->nr_dirtied),
+ K(stats->nr_written),
+ K(wb->avg_write_bandwidth),
+ stats->nr_dirty,
+ stats->nr_io,
+ stats->nr_more_io,
+ stats->nr_dirty_time,
+ wb->state);
+}
+
+static int cgwb_debug_stats_show(struct seq_file *m, void *v)
+{
+ struct backing_dev_info *bdi;
+ unsigned long background_thresh;
+ unsigned long dirty_thresh;
+ struct bdi_writeback *wb;
+ struct wb_stats stats;
+
+ rcu_read_lock();
+ bdi = lookup_bdi(m);
+ if (!bdi) {
+ rcu_read_unlock();
+ return -EEXIST;
+ }
+
+ global_dirty_limits(&background_thresh, &dirty_thresh);
+
+ list_for_each_entry_rcu(wb, &bdi->wb_list, bdi_node) {
+ memset(&stats, 0, sizeof(stats));
+ stats.dirty_thresh = dirty_thresh;
+ collect_wb_stats(&stats, wb);
+
+ if (mem_cgroup_wb_domain(wb) == NULL) {
+ wb_stats_show(m, wb, &stats);
+ continue;
+ }
+
+ /*
+ * cgwb_release will destroy wb->memcg_completions which
+ * will be ued in cgwb_calc_thresh. Use wb_tryget to prevent
+ * memcg_completions destruction from cgwb_release.
+ */
+ if (!wb_tryget(wb))
+ continue;
+
+ rcu_read_unlock();
+ /* cgwb_calc_thresh may sleep in cgroup_rstat_flush */
+ stats.wb_thresh = min(stats.wb_thresh, cgwb_calc_thresh(wb));
+ wb_stats_show(m, wb, &stats);
+ rcu_read_lock();
+ wb_put(wb);
+ }
+ rcu_read_unlock();
+
+ return 0;
+}
+DEFINE_SHOW_ATTRIBUTE(cgwb_debug_stats);
+
+static void cgwb_debug_register(struct backing_dev_info *bdi)
+{
+ debugfs_create_file("wb_stats", 0444, bdi->debug_dir, bdi,
+ &cgwb_debug_stats_fops);
+}
+
static void bdi_collect_stats(struct backing_dev_info *bdi,
struct wb_stats *stats)
{
@@ -117,6 +202,8 @@ static void bdi_collect_stats(struct backing_dev_info *bdi,
{
collect_wb_stats(stats, &bdi->wb);
}
+
+static inline void cgwb_debug_register(struct backing_dev_info *bdi) { }
#endif
static int bdi_debug_stats_show(struct seq_file *m, void *v)
@@ -182,6 +269,7 @@ static void bdi_debug_register(struct backing_dev_info *bdi, const char *name)
debugfs_create_file("stats", 0444, bdi->debug_dir, bdi,
&bdi_debug_stats_fops);
+ cgwb_debug_register(bdi);
}
static void bdi_debug_unregister(struct backing_dev_info *bdi)
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 0e20467367fe..3724c7525316 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -893,6 +893,25 @@ unsigned long wb_calc_thresh(struct bdi_writeback *wb, unsigned long thresh)
return __wb_calc_thresh(&gdtc, thresh);
}
+unsigned long cgwb_calc_thresh(struct bdi_writeback *wb)
+{
+ struct dirty_throttle_control gdtc = { GDTC_INIT_NO_WB };
+ struct dirty_throttle_control mdtc = { MDTC_INIT(wb, &gdtc) };
+ unsigned long filepages, headroom, writeback;
+
+ gdtc.avail = global_dirtyable_memory();
+ gdtc.dirty = global_node_page_state(NR_FILE_DIRTY) +
+ global_node_page_state(NR_WRITEBACK);
+
+ mem_cgroup_wb_stats(wb, &filepages, &headroom,
+ &mdtc.dirty, &writeback);
+ mdtc.dirty += writeback;
+ mdtc_calc_avail(&mdtc, filepages, headroom);
+ domain_dirty_limits(&mdtc);
+
+ return __wb_calc_thresh(&mdtc, mdtc.thresh);
+}
+
/*
* setpoint - dirty 3
* f(dirty) := 1.0 + (----------------)
--
2.30.0