The rss_stat tracepoint is emitted on every RSS update, including each
page fault. When it is enabled, it reports the precise sum of the RSS
counter, which iterates over all possible CPUs for each event: 384 per
page fault on a machine with 384 logical CPUs.
Report the approximate sum of the hierarchical per-cpu counter instead,
through get_mm_counter(), which reads the root of the counter tree. The
size field of the event, the RSS counter after the update, is therefore
within the accuracy bound of the counter from the precise value: within
158.5MB on a machine with 384 logical CPUs and 4kB pages.
The tracepoint reports the precise sum since commit f1a7941243c1 ("mm:
convert mm's rss stats into percpu_counter"). Before that, it reported
an atomic counter which only received the per-task cached updates in
batches.
Signed-off-by: Mathieu Desnoyers <[email protected]>
Cc: "Paul E. McKenney" <[email protected]>
Cc: Steven Rostedt <[email protected]>
Cc: Masami Hiramatsu <[email protected]>
Cc: Dennis Zhou <[email protected]>
Cc: Tejun Heo <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: Martin Liu <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: [email protected]
Cc: Shakeel Butt <[email protected]>
Cc: SeongJae Park <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Sweet Tea Dorminy <[email protected]>
Cc: Lorenzo Stoakes <[email protected]>
Cc: Liam R. Howlett <[email protected]>
Cc: Mike Rapoport <[email protected]>
Cc: Suren Baghdasaryan <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Christian Brauner <[email protected]>
Cc: Wei Yang <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Miaohe Lin <[email protected]>
Cc: Al Viro <[email protected]>
Cc: Yu Zhao <[email protected]>
Cc: Roman Gushchin <[email protected]>
Cc: Mateusz Guzik <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: Baolin Wang <[email protected]>
Cc: Aboorva Devarajan <[email protected]>
Cc: David Carlier <[email protected]>
Cc: Josh Law <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: [email protected]
---
Changes since v22:
- Split from "mm: improve RSS counter approximation accuracy for proc
interfaces", which now keeps reporting the precise sum.
---
include/trace/events/kmem.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/include/trace/events/kmem.h b/include/trace/events/kmem.h
index ac4c96db7638..8ee6d5df5961 100644
--- a/include/trace/events/kmem.h
+++ b/include/trace/events/kmem.h
@@ -448,7 +448,7 @@ TRACE_EVENT(rss_stat,
*/
__entry->curr = current->mm == mm && !(current->flags &
PF_KTHREAD);
__entry->member = member;
- __entry->size = get_mm_counter_sum(mm, member) << PAGE_SHIFT;
+ __entry->size = get_mm_counter(mm, member) << PAGE_SHIFT;
),
TP_printk("mm_id=%u curr=%d type=%s size=%ldB",
--
2.47.3
