From 094470f3f45b9efdab2c6b27f920071e29ebf5c5 Mon Sep 17 00:00:00 2001 From: JP Kobryn Date: Mon, 22 Jun 2026 11:51:27 -0700 Subject: [PATCH] mm/lruvec: trace LRU add drains and drain-all requests 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_add_drain_all to capture callers of __lru_add_drain_all and whether they set the force flag for all CPUs. The tracepoint resembles the signature of the enclosing function, but is needed because of potential inlining. Note that DECLARE_TRACE() is used for these new trace hooks to avoid creating a new trace event ABI. Link: https://lore.kernel.org/20260622185127.24579-1-jp.kobryn@linux.dev Signed-off-by: JP Kobryn Reviewed-by: Barry Song Acked-by: Shakeel Butt Cc: Axel Rasmussen Cc: Baoquan He Cc: Chris Li Cc: Kairui Song Cc: Kemeng Shi Cc: "Masami Hiramatsu (Google)" Cc: Mathieu Desnoyers Cc: Matthew Wilcox (Oracle) Cc: Michal Hocko Cc: Nhat Pham Cc: Steven Rostedt Cc: Vlastimil Babka Cc: Wei Xu Cc: Yuanchu Xie Signed-off-by: Andrew Morton --- include/trace/events/pagemap.h | 8 ++++++++ mm/swap.c | 7 ++++++- 2 files changed, 14 insertions(+), 1 deletion(-) diff --git a/include/trace/events/pagemap.h b/include/trace/events/pagemap.h index 171524d3526d..36c3a90f0acc 100644 --- a/include/trace/events/pagemap.h +++ b/include/trace/events/pagemap.h @@ -77,6 +77,14 @@ TRACE_EVENT(mm_lru_activate, TP_printk("folio=%p pfn=0x%lx", __entry->folio, __entry->pfn) ); +DECLARE_TRACE(mm_lru_add_drain, + TP_PROTO(int cpu, unsigned int nr_folios), + TP_ARGS(cpu, nr_folios)); + +DECLARE_TRACE(mm_lru_add_drain_all, + TP_PROTO(bool force_all_cpus), + TP_ARGS(force_all_cpus)); + #endif /* _TRACE_PAGEMAP_H */ /* This part must be outside protection */ diff --git a/mm/swap.c b/mm/swap.c index 588f50d8f1a8..460e56370b3c 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 = folio_batch_count(fbatch); - if (folio_batch_count(fbatch)) + if (nr_folios) { folio_batch_move_lru(fbatch, lru_add); + trace_mm_lru_add_drain_tp(cpu, nr_folios); + } fbatch = &fbatches->lru_move_tail; /* Disabling interrupts below acts as a compiler barrier. */ @@ -869,6 +872,8 @@ static inline void __lru_add_drain_all(bool force_all_cpus) if (WARN_ON(!mm_percpu_wq)) return; + trace_mm_lru_add_drain_all_tp(force_all_cpus); + /* * Guarantee folio_batch counter stores visible by this CPU * are visible to other CPUs before loading the current drain