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. Signed-off-by: JP Kobryn <[email protected]> Reviewed-by: Barry Song <[email protected]> Acked-by: Shakeel Butt <[email protected]> --- v5: - change from trace events to bare trace hooks v4: https://lore.kernel.org/linux-mm/[email protected]/ - renamed nr_folio_add to nr_folios in lru_add_drain() - renamed nr to nr_folios in tracepoint for consistency v3: https://lore.kernel.org/linux-mm/[email protected]/ - restored and renamed tracepoint in __lru_add_drain_all v2: https://lore.kernel.org/linux-mm/[email protected]/ - removed mm_lru_drain_all tracepoint v1: https://lore.kernel.org/linux-mm/[email protected]/ 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 -- 2.54.0
