LRU add batches can be drained before they reach capacity. This can be a source of LRU lock contention, but it is not currently possible to attribute these drains to callers with existing tracepoints.
Add mm_lru_add_drain to report the CPU and lru_add batch count when an lru_add batch is drained. This allows tracing to distinguish full drains from partial drains and attribute them to the calling stack. Add mm_lru_drain_all_queue to report when lru_add_drain_all() queues per-CPU drain work. This captures the requester stack and target CPU for remote drain work. The event is named as a drain-all queue event because the queued work can be needed for batches other than lru_add. Signed-off-by: JP Kobryn <[email protected]> --- include/trace/events/pagemap.h | 40 ++++++++++++++++++++++++++++++++++ mm/swap.c | 6 ++++- 2 files changed, 45 insertions(+), 1 deletion(-) diff --git a/include/trace/events/pagemap.h b/include/trace/events/pagemap.h index 171524d3526d..ea8fc46bedb0 100644 --- a/include/trace/events/pagemap.h +++ b/include/trace/events/pagemap.h @@ -77,6 +77,46 @@ TRACE_EVENT(mm_lru_activate, TP_printk("folio=%p pfn=0x%lx", __entry->folio, __entry->pfn) ); +TRACE_EVENT(mm_lru_add_drain, + + TP_PROTO(int cpu, unsigned int nr), + + TP_ARGS(cpu, nr), + + TP_STRUCT__entry( + __field(int, cpu ) + __field(unsigned int, nr ) + ), + + TP_fast_assign( + __entry->cpu = cpu; + __entry->nr = nr; + ), + + TP_printk("cpu=%d nr=%u", __entry->cpu, __entry->nr) +); + +TRACE_EVENT(mm_lru_drain_all_queue, + + TP_PROTO(int target_cpu, bool force_all_cpus), + + TP_ARGS(target_cpu, force_all_cpus), + + TP_STRUCT__entry( + __field(int, target_cpu ) + __field(bool, force_all_cpus ) + ), + + TP_fast_assign( + __entry->target_cpu = target_cpu; + __entry->force_all_cpus = force_all_cpus; + ), + + TP_printk("target_cpu=%d force_all_cpus=%s", + __entry->target_cpu, + __entry->force_all_cpus ? "true" : "false") +); + #endif /* _TRACE_PAGEMAP_H */ /* This part must be outside protection */ diff --git a/mm/swap.c b/mm/swap.c index 588f50d8f1a8..c385b93582eb 100644 --- a/mm/swap.c +++ b/mm/swap.c @@ -694,9 +694,12 @@ void lru_add_drain_cpu(int cpu) { struct cpu_fbatches *fbatches = &per_cpu(cpu_fbatches, cpu); struct folio_batch *fbatch = &fbatches->lru_add; + unsigned int nr_folios_add = folio_batch_count(fbatch); - if (folio_batch_count(fbatch)) + if (nr_folios_add) { folio_batch_move_lru(fbatch, lru_add); + trace_mm_lru_add_drain(cpu, nr_folios_add); + } fbatch = &fbatches->lru_move_tail; /* Disabling interrupts below acts as a compiler barrier. */ @@ -928,6 +931,7 @@ static inline void __lru_add_drain_all(bool force_all_cpus) if (cpu_needs_drain(cpu)) { INIT_WORK(work, lru_add_drain_per_cpu); queue_work_on(cpu, mm_percpu_wq, work); + trace_mm_lru_drain_all_queue(cpu, force_all_cpus); __cpumask_set_cpu(cpu, &has_work); } } -- 2.54.0
