mm/vmscan: add balance_pgdat begin/end tracepoints

Vmscan has six main reclaim entry points: try_to_free_pages() for
direct reclaim, try_to_free_mem_cgroup_pages() for memcg reclaim,
mem_cgroup_shrink_node() for memcg soft limit reclaim, node_reclaim()
for node reclaim, shrink_all_memory() for hibernation reclaim, and
balance_pgdat() for kswapd reclaim.

All of them, except for shrink_all_memory() and balance_pgdat(),
already have begin/end tracepoints.  This makes it harder to trace
which reclaim path is responsible for memory reclaim activity, because
kswapd reclaim cannot be identified as cleanly as other reclaim entry
points, even though it is the main background reclaim path under memory
pressure.  There may be no need to trace shrink_all_memory() as it is
primarily used during hibernation.  So this patch adds the missing
tracepoint pair for balance_pgdat().

The begin tracepoint records the node id, requested reclaim order, and
the requested classzone bound (highest_zoneidx).  The end tracepoint
records the node id, the reclaim order that balance_pgdat() finished
with, the requested classzone bound, and nr_reclaimed.  Together, they
show the requested reclaim order and classzone bound, whether reclaim
fell back to a lower order, and how much reclaim work was done.

The end tracepoint also records highest_zoneidx even though it does not
change within a balance_pgdat() invocation.  This keeps the end event
self-contained, so users can analyze reclaim results directly from end
events without depending on begin/end correlation, which is less
convenient when tracing is filtered or records are dropped.  It also
makes it straightforward to relate nr_reclaimed and the final reclaim
order to the requested classzone bound.

Link: https://lore.kernel.org/20260424031418.174597-1-b.suvonov@sjtu.edu.cn
Link: https://lore.kernel.org/20260423103753.546582-1-b.suvonov@sjtu.edu.cn
Signed-off-by: Bunyod Suvonov <b.suvonov@sjtu.edu.cn>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Barry Song <baohua@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kairui Song <kasong@tencent.com>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Wei Xu <weixugc@google.com>
Cc: Yuanchu Xie <yuanchu@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/include/trace/events/vmscan.h b/include/trace/events/vmscan.h
index 4445a8d9218de460fd56fd5e2c6c68daa6b0967e..b4bf7b8def1f5f2b269af66cae27cbf7e8a062eb 100644 (file)
--- a/include/trace/events/vmscan.h
+++ b/include/trace/events/vmscan.h
@@ -96,6 +96,58 @@ TRACE_EVENT(mm_vmscan_kswapd_wake,
                __entry->order)
 );
 
+TRACE_EVENT(mm_vmscan_balance_pgdat_begin,
+
+       TP_PROTO(int nid, int order, int highest_zoneidx),
+
+       TP_ARGS(nid, order, highest_zoneidx),
+
+       TP_STRUCT__entry(
+               __field(int, nid)
+               __field(int, order)
+               __field(int, highest_zoneidx)
+       ),
+
+       TP_fast_assign(
+               __entry->nid = nid;
+               __entry->order = order;
+               __entry->highest_zoneidx = highest_zoneidx;
+       ),
+
+       TP_printk("nid=%d order=%d highest_zoneidx=%-8s",
+               __entry->nid,
+               __entry->order,
+               __print_symbolic(__entry->highest_zoneidx, ZONE_TYPE))
+);
+
+TRACE_EVENT(mm_vmscan_balance_pgdat_end,
+
+       TP_PROTO(int nid, int order, int highest_zoneidx,
+                unsigned long nr_reclaimed),
+
+       TP_ARGS(nid, order, highest_zoneidx, nr_reclaimed),
+
+       TP_STRUCT__entry(
+               __field(int, nid)
+               __field(int, order)
+               __field(int, highest_zoneidx)
+               __field(unsigned long, nr_reclaimed)
+       ),
+
+       TP_fast_assign(
+               __entry->nid = nid;
+               __entry->order = order;
+               __entry->highest_zoneidx = highest_zoneidx;
+               __entry->nr_reclaimed = nr_reclaimed;
+       ),
+
+       TP_printk("nid=%d order=%d highest_zoneidx=%-8s nr_reclaimed=%lu",
+               __entry->nid,
+               __entry->order,
+               __print_symbolic(__entry->highest_zoneidx, ZONE_TYPE),
+               __entry->nr_reclaimed)
+);
+
 TRACE_EVENT(mm_vmscan_wakeup_kswapd,
 
        TP_PROTO(int nid, int zid, int order, gfp_t gfp_flags),

diff --git a/mm/vmscan.c b/mm/vmscan.c
index bd1b1aa125819fe3c166bd1c015e6432d58cfdf4..b2d89ed69d228b72e4c9bf2ef1b595c78cd8129e 100644 (file)
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -7121,6 +7121,8 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int highest_zoneidx)
                .may_unmap = 1,
        };
 
+       trace_mm_vmscan_balance_pgdat_begin(pgdat->node_id, order,
+                                           highest_zoneidx);
        set_task_reclaim_state(current, &sc.reclaim_state);
        psi_memstall_enter(&pflags);
        __fs_reclaim_acquire(_THIS_IP_);
@@ -7314,6 +7316,9 @@ out:
        psi_memstall_leave(&pflags);
        set_task_reclaim_state(current, NULL);
 
+       trace_mm_vmscan_balance_pgdat_end(pgdat->node_id, sc.order,
+                                         highest_zoneidx, sc.nr_reclaimed);
+
        /*
         * Return the order kswapd stopped reclaiming at as
         * prepare_kswapd_sleep() takes it into account. If another caller