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. Signed-off-by: JP Kobryn <[email protected]> --- v2: - removed mm_lru_drain_all tracepoint v1: https://lore.kernel.org/linux-mm/[email protected]/ include/trace/events/pagemap.h | 19 +++++++++++++++++++ mm/swap.c | 5 ++++- 2 files changed, 23 insertions(+), 1 deletion(-) diff --git a/include/trace/events/pagemap.h b/include/trace/events/pagemap.h index 171524d3526d..fc28745507be 100644 --- a/include/trace/events/pagemap.h +++ b/include/trace/events/pagemap.h @@ -77,6 +77,25 @@ 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) +); + #endif /* _TRACE_PAGEMAP_H */ /* This part must be outside protection */ diff --git a/mm/swap.c b/mm/swap.c index 588f50d8f1a8..8fd6808bfc6e 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. */ -- 2.54.0
