On 6/11/26 01:48, JP Kobryn wrote: > 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. > > Signed-off-by: JP Kobryn <[email protected]> > Reviewed-by: Barry Song <[email protected]> > Acked-by: Shakeel Butt <[email protected]>
Acked-by: Vlastimil Babka (SUSE) <[email protected]> > --- > v4: > - 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 | 37 ++++++++++++++++++++++++++++++++++ > mm/swap.c | 7 ++++++- > 2 files changed, 43 insertions(+), 1 deletion(-) > > diff --git a/include/trace/events/pagemap.h b/include/trace/events/pagemap.h > index 171524d3526d..df6ac4d13dcf 100644 > --- a/include/trace/events/pagemap.h > +++ b/include/trace/events/pagemap.h > @@ -77,6 +77,43 @@ 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_folios), > + > + TP_ARGS(cpu, nr_folios), > + > + TP_STRUCT__entry( > + __field(int, cpu ) > + __field(unsigned int, nr_folios ) > + ), > + > + TP_fast_assign( > + __entry->cpu = cpu; > + __entry->nr_folios = nr_folios; > + ), > + > + TP_printk("cpu=%d nr_folios=%u", __entry->cpu, __entry->nr_folios) > +); > + > +TRACE_EVENT(mm_lru_add_drain_all, > + > + TP_PROTO(bool force_all_cpus), > + > + TP_ARGS(force_all_cpus), > + > + TP_STRUCT__entry( > + __field(bool, force_all_cpus ) > + ), > + > + TP_fast_assign( > + __entry->force_all_cpus = force_all_cpus; > + ), > + > + TP_printk("force_all_cpus=%s", > + __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..b506fa912a93 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(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(force_all_cpus); > + > /* > * Guarantee folio_batch counter stores visible by this CPU > * are visible to other CPUs before loading the current drain
