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mm/lruvec: trace LRU add drains and drain-all requests

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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 <jp.kobryn@linux.dev>
Reviewed-by: Barry Song <baohua@kernel.org>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Baoquan He <baoquan.he@linux.dev>
Cc: Chris Li <chrisl@kernel.org>
Cc: Kairui Song <kasong@tencent.com>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Wei Xu <weixugc@google.com>
Cc: Yuanchu Xie <yuanchu@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
JP Kobryn 2026-06-22 11:51:27 -07:00 committed by Andrew Morton
parent 4ac732c370
commit 094470f3f4
2 changed files with 14 additions and 1 deletions
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8
include/trace/events/pagemap.h
View File

@ -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 */

7
mm/swap.c
View File

@ -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