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Subject[PATCH block/for-next] writeback: add tracepoints for cgroup foreign writebacks
cgroup foreign inode handling has quite a bit of heuristics and
internal states which sometimes makes it difficult to understand
what's going on. Add tracepoints to improve visibility.

Signed-off-by: Tejun Heo <tj@kernel.org>
---
fs/fs-writeback.c | 5 +
include/trace/events/writeback.h | 123 +++++++++++++++++++++++++++++++++++++++
mm/memcontrol.c | 5 +
3 files changed, 133 insertions(+)

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 658dc16c9e6d..8aaa7eec7b74 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -389,6 +389,8 @@ static void inode_switch_wbs_work_fn(struct work_struct *work)
if (unlikely(inode->i_state & I_FREEING))
goto skip_switch;

+ trace_inode_switch_wbs(inode, old_wb, new_wb);
+
/*
* Count and transfer stats. Note that PAGECACHE_TAG_DIRTY points
* to possibly dirty pages while PAGECACHE_TAG_WRITEBACK points to
@@ -673,6 +675,9 @@ void wbc_detach_inode(struct writeback_control *wbc)
if (wbc->wb_id != max_id)
history |= (1U << slots) - 1;

+ if (history)
+ trace_inode_foreign_history(inode, wbc, history);
+
/*
* Switch if the current wb isn't the consistent winner.
* If there are multiple closely competing dirtiers, the
diff --git a/include/trace/events/writeback.h b/include/trace/events/writeback.h
index aa7f3aeac740..3dc9fb9e7c78 100644
--- a/include/trace/events/writeback.h
+++ b/include/trace/events/writeback.h
@@ -176,6 +176,129 @@ static inline unsigned int __trace_wbc_assign_cgroup(struct writeback_control *w
#endif /* CONFIG_CGROUP_WRITEBACK */
#endif /* CREATE_TRACE_POINTS */

+#ifdef CONFIG_CGROUP_WRITEBACK
+TRACE_EVENT(inode_foreign_history,
+
+ TP_PROTO(struct inode *inode, struct writeback_control *wbc,
+ unsigned int history),
+
+ TP_ARGS(inode, wbc, history),
+
+ TP_STRUCT__entry(
+ __array(char, name, 32)
+ __field(unsigned long, ino)
+ __field(unsigned int, cgroup_ino)
+ __field(unsigned int, history)
+ ),
+
+ TP_fast_assign(
+ strncpy(__entry->name, dev_name(inode_to_bdi(inode)->dev), 32);
+ __entry->ino = inode->i_ino;
+ __entry->cgroup_ino = __trace_wbc_assign_cgroup(wbc);
+ __entry->history = history;
+ ),
+
+ TP_printk("bdi %s: ino=%lu cgroup_ino=%u history=0x%x",
+ __entry->name,
+ __entry->ino,
+ __entry->cgroup_ino,
+ __entry->history
+ )
+);
+
+TRACE_EVENT(inode_switch_wbs,
+
+ TP_PROTO(struct inode *inode, struct bdi_writeback *old_wb,
+ struct bdi_writeback *new_wb),
+
+ TP_ARGS(inode, old_wb, new_wb),
+
+ TP_STRUCT__entry(
+ __array(char, name, 32)
+ __field(unsigned long, ino)
+ __field(unsigned int, old_cgroup_ino)
+ __field(unsigned int, new_cgroup_ino)
+ ),
+
+ TP_fast_assign(
+ strncpy(__entry->name, dev_name(old_wb->bdi->dev), 32);
+ __entry->ino = inode->i_ino;
+ __entry->old_cgroup_ino = __trace_wb_assign_cgroup(old_wb);
+ __entry->new_cgroup_ino = __trace_wb_assign_cgroup(new_wb);
+ ),
+
+ TP_printk("bdi %s: ino=%lu old_cgroup_ino=%u new_cgroup_ino=%u",
+ __entry->name,
+ __entry->ino,
+ __entry->old_cgroup_ino,
+ __entry->new_cgroup_ino
+ )
+);
+
+TRACE_EVENT(track_foreign_dirty,
+
+ TP_PROTO(struct page *page, struct bdi_writeback *wb),
+
+ TP_ARGS(page, wb),
+
+ TP_STRUCT__entry(
+ __array(char, name, 32)
+ __field(u64, bdi_id)
+ __field(unsigned long, ino)
+ __field(unsigned int, memcg_id)
+ __field(unsigned int, cgroup_ino)
+ __field(unsigned int, page_cgroup_ino)
+ ),
+
+ TP_fast_assign(
+ strncpy(__entry->name, dev_name(wb->bdi->dev), 32);
+ __entry->bdi_id = wb->bdi->id;
+ __entry->ino = page->mapping->host->i_ino;
+ __entry->memcg_id = wb->memcg_css->id;
+ __entry->cgroup_ino = __trace_wb_assign_cgroup(wb);
+ __entry->page_cgroup_ino = page->mem_cgroup->css.cgroup->kn->id.ino;
+ ),
+
+ TP_printk("bdi %s[%llu]: ino=%lu memcg_id=%u cgroup_ino=%u page_cgroup_ino=%u",
+ __entry->name,
+ __entry->bdi_id,
+ __entry->ino,
+ __entry->memcg_id,
+ __entry->cgroup_ino,
+ __entry->page_cgroup_ino
+ )
+);
+
+TRACE_EVENT(flush_foreign,
+
+ TP_PROTO(struct bdi_writeback *wb, unsigned int frn_bdi_id,
+ unsigned int frn_memcg_id),
+
+ TP_ARGS(wb, frn_bdi_id, frn_memcg_id),
+
+ TP_STRUCT__entry(
+ __array(char, name, 32)
+ __field(unsigned int, cgroup_ino)
+ __field(unsigned int, frn_bdi_id)
+ __field(unsigned int, frn_memcg_id)
+ ),
+
+ TP_fast_assign(
+ strncpy(__entry->name, dev_name(wb->bdi->dev), 32);
+ __entry->cgroup_ino = __trace_wb_assign_cgroup(wb);
+ __entry->frn_bdi_id = frn_bdi_id;
+ __entry->frn_memcg_id = frn_memcg_id;
+ ),
+
+ TP_printk("bdi %s: cgroup_ino=%u frn_bdi_id=%u frn_memcg_id=%u",
+ __entry->name,
+ __entry->cgroup_ino,
+ __entry->frn_bdi_id,
+ __entry->frn_memcg_id
+ )
+);
+#endif
+
DECLARE_EVENT_CLASS(writeback_write_inode_template,

TP_PROTO(struct inode *inode, struct writeback_control *wbc),
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index eb626a290d93..b74c9d143d5e 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4159,6 +4159,8 @@ static int mem_cgroup_oom_control_write(struct cgroup_subsys_state *css,

#ifdef CONFIG_CGROUP_WRITEBACK

+#include <trace/events/writeback.h>
+
static int memcg_wb_domain_init(struct mem_cgroup *memcg, gfp_t gfp)
{
return wb_domain_init(&memcg->cgwb_domain, gfp);
@@ -4296,6 +4298,8 @@ void mem_cgroup_track_foreign_dirty_slowpath(struct page *page,
int oldest = -1;
int i;

+ trace_track_foreign_dirty(page, wb);
+
/*
* Pick the slot to use. If there is already a slot for @wb, keep
* using it. If not replace the oldest one which isn't being
@@ -4356,6 +4360,7 @@ void mem_cgroup_flush_foreign(struct bdi_writeback *wb)
if (time_after64(frn->at, now - intv) &&
atomic_read(&frn->done.cnt) == 1) {
frn->at = 0;
+ trace_flush_foreign(wb, frn->bdi_id, frn->memcg_id);
cgroup_writeback_by_id(frn->bdi_id, frn->memcg_id, 0,
WB_REASON_FOREIGN_FLUSH,
&frn->done);
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