Re: [PATCH] mm/damon: add damos_node_eligible_mem_bp tracepoint
flat view
From: Steven Rostedt <rostedt@goodmis.org>
Date: 2026-10-04 09:16:46
Also in:
damon, linux-mm, lkml
On Sat, 3 Oct 2026 13:27:27 -0700 Ravi Jonnalagadda [off-list ref] wrote:
quoted hunk ↗ jump to hunk
Add a tracepoint for DAMOS_QUOTA_NODE_ELIGIBLE_MEM_BP quota goal evaluation. The tracepoint fires once per quota-score computation when the goal metric is DAMOS_QUOTA_NODE_ELIGIBLE_MEM_BP, exposing context_idx, scheme_idx, nid, target_value, and current_value. current_value is reported as the quota tuning sees it, after the goal's complement setting is applied. The DAMOS_QUOTA_NODE_ELIGIBLE_MEM_BP metric expresses node memory occupancy as basis points of eligible bytes. This information is not exposed through any existing external interface (perf stat, /proc, or sysfs), so the tracepoint is the only way for userspace to observe the target and current eligible-memory basis point values at quota-scoring time. Link: https://lore.kernel.org/linux-mm/20260428030520.701-1-ravis.opensrc@gmail.com/ (local) Signed-off-by: Ravi Jonnalagadda <redacted> --- include/trace/events/damon.h | 31 +++++++++++++++++++++++++++++++ mm/damon/core.c | 16 ++++++++++++++++ 2 files changed, 47 insertions(+)diff --git a/include/trace/events/damon.h b/include/trace/events/damon.h index 8851727ae162..2c7249cc7c88 100644 --- a/include/trace/events/damon.h +++ b/include/trace/events/damon.h@@ -74,6 +74,37 @@ TRACE_EVENT(damos_esz, __entry->esz) ); +/* Per-tick DAMOS_QUOTA_NODE_ELIGIBLE_MEM_BP goal evaluation. */ +TRACE_EVENT(damos_node_eligible_mem_bp, + + TP_PROTO(unsigned int context_idx, unsigned int scheme_idx, + int nid, + unsigned long target_value, unsigned long current_value), + + TP_ARGS(context_idx, scheme_idx, nid, target_value, current_value), + + TP_STRUCT__entry( + __field(unsigned int, context_idx) + __field(unsigned int, scheme_idx) + __field(int, nid)
Can you move the nid after the two unsigned long values below. This creates a structure, and on 64bit machines, this adds a 4 byte padding in the middle of the ring buffer.
quoted hunk ↗ jump to hunk
+ __field(unsigned long, target_value) + __field(unsigned long, current_value) + ), + + TP_fast_assign( + __entry->context_idx = context_idx; + __entry->scheme_idx = scheme_idx; + __entry->nid = nid; + __entry->target_value = target_value; + __entry->current_value = current_value; + ), + + TP_printk("ctx_idx=%u scheme_idx=%u nid=%d target_value=%lu current_value=%lu", + __entry->context_idx, __entry->scheme_idx, + __entry->nid, + __entry->target_value, __entry->current_value) +); + TRACE_EVENT_CONDITION(damos_before_apply, TP_PROTO(unsigned int context_idx, unsigned int scheme_idx,diff --git a/mm/damon/core.c b/mm/damon/core.c index b63e60ef8990..6ddd15dc4f55 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c@@ -3294,6 +3294,22 @@ static unsigned long damos_quota_score(struct damon_ctx *c, struct damos *s) highest_score = max(highest_score, mult_frac(goal->current_value, 10000, goal->target_value)); + + if (goal->metric == DAMOS_QUOTA_NODE_ELIGIBLE_MEM_BP && + trace_damos_node_eligible_mem_bp_enabled()) {
If you move the trace_damos_node_eligible_mem_bp_enabled() before the goal->metric check, you will save yourself a branch when tracing is off. As the trace_*_enabled() is a static branch (nop or jmp) it has no cmp branch, but the above will keep the goal->metric still exposed. By swapping the two compares, the goal->metric check will be hidder behind the 'nop' when tracing is disabled. -- Steve
+ unsigned int cidx = 0, sidx = 0;
+ struct damos *siter;
+
+ damon_for_each_scheme(siter, c) {
+ if (siter == s)
+ break;
+ sidx++;
+ }
+ trace_damos_node_eligible_mem_bp(cidx, sidx,
+ goal->nid,
+ goal->target_value,
+ goal->current_value);
+ }
}
return highest_score;
base-commit: 763ad0211c7b587344f03bc4d1299810aeb736f4