[PATCH 08/13] writeback: add support to collect stats for all writeback ctxs

Kundan Kumar
2025-05-29T11:34:07Z

Modified stats collection to collect stats for all the writeback
contexts within a bdi.

Signed-off-by: Kundan Kumar <kundan.kumar@samsung.com>
Signed-off-by: Anuj Gupta <anuj20.g@samsung.com>
---
mm/backing-dev.c | 72 ++++++++++++++++++++++++++++--------------------
1 file changed, 42 insertions(+), 30 deletions(-)

diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 5479e2d34160..d416122e2914 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -50,6 +50,7 @@ struct wb_stats {
unsigned long nr_written;
unsigned long dirty_thresh;
unsigned long wb_thresh;
+ unsigned long state;
};

static struct dentry *bdi_debug_root;
@@ -81,6 +82,7 @@ static void collect_wb_stats(struct wb_stats *stats,
stats->nr_dirtied += wb_stat(wb, WB_DIRTIED);
stats->nr_written += wb_stat(wb, WB_WRITTEN);
stats->wb_thresh += wb_calc_thresh(wb, stats->dirty_thresh);
+ stats->state |= wb->state;
}

#ifdef CONFIG_CGROUP_WRITEBACK
@@ -89,22 +91,27 @@ static void bdi_collect_stats(struct backing_dev_info *bdi,
struct wb_stats *stats)
{
struct bdi_writeback *wb;
+ struct bdi_writeback_ctx *bdi_wb_ctx;

rcu_read_lock();
- list_for_each_entry_rcu(wb, &bdi->wb_ctx_arr[0]->wb_list, bdi_node) {
- if (!wb_tryget(wb))
- continue;
+ for_each_bdi_wb_ctx(bdi, bdi_wb_ctx)
+ list_for_each_entry_rcu(wb, &bdi_wb_ctx->wb_list, bdi_node) {
+ if (!wb_tryget(wb))
+ continue;

- collect_wb_stats(stats, wb);
- wb_put(wb);
- }
+ collect_wb_stats(stats, wb);
+ wb_put(wb);
+ }
rcu_read_unlock();
}
#else
static void bdi_collect_stats(struct backing_dev_info *bdi,
struct wb_stats *stats)
{
- collect_wb_stats(stats, &bdi->wb_ctx_arr[0]->wb);
+ struct bdi_writeback_ctx *bdi_wb_ctx;
+
+ for_each_bdi_wb_ctx(bdi, bdi_wb_ctx)
+ collect_wb_stats(stats, &bdi_wb_ctx->wb);
}
#endif

@@ -150,7 +157,7 @@ static int bdi_debug_stats_show(struct seq_file *m, void *v)
stats.nr_io,
stats.nr_more_io,
stats.nr_dirty_time,
- !list_empty(&bdi->bdi_list), bdi->wb_ctx_arr[0]->wb.state);
+ !list_empty(&bdi->bdi_list), stats.state);

return 0;
}
@@ -195,35 +202,40 @@ static int cgwb_debug_stats_show(struct seq_file *m, void *v)
{
struct backing_dev_info *bdi = m->private;
struct bdi_writeback *wb;
+ struct bdi_writeback_ctx *bdi_wb_ctx;
unsigned long background_thresh;
unsigned long dirty_thresh;
+ struct wb_stats stats;

global_dirty_limits(&background_thresh, &dirty_thresh);
+ stats.dirty_thresh = dirty_thresh;

rcu_read_lock();
- list_for_each_entry_rcu(wb, &bdi->wb_ctx_arr[0]->wb_list, bdi_node) {
- struct wb_stats stats = { .dirty_thresh = dirty_thresh };
-
- if (!wb_tryget(wb))
- continue;
-
- collect_wb_stats(&stats, wb);
-
- /*
- * Calculate thresh of wb in writeback cgroup which is min of
- * thresh in global domain and thresh in cgroup domain. Drop
- * rcu lock because cgwb_calc_thresh may sleep in
- * cgroup_rstat_flush. We can do so here because we have a ref.
- */
- if (mem_cgroup_wb_domain(wb)) {
- rcu_read_unlock();
- stats.wb_thresh = min(stats.wb_thresh, cgwb_calc_thresh(wb));
- rcu_read_lock();
+ for_each_bdi_wb_ctx(bdi, bdi_wb_ctx) {
+ list_for_each_entry_rcu(wb, &bdi_wb_ctx->wb_list, bdi_node) {
+ if (!wb_tryget(wb))
+ continue;
+
+ collect_wb_stats(&stats, wb);
+
+ /*
+ * Calculate thresh of wb in writeback cgroup which is
+ * min of thresh in global domain and thresh in cgroup
+ * domain. Drop rcu lock because cgwb_calc_thresh may
+ * sleep in cgroup_rstat_flush. We can do so here
+ * because we have a ref.
+ */
+ if (mem_cgroup_wb_domain(wb)) {
+ rcu_read_unlock();
+ stats.wb_thresh = min(stats.wb_thresh,
+ cgwb_calc_thresh(wb));
+ rcu_read_lock();
+ }
+
+ wb_stats_show(m, wb, &stats);
+
+ wb_put(wb);
}
-
- wb_stats_show(m, wb, &stats);
-
- wb_put(wb);
}
rcu_read_unlock();

--
2.25.1