vmscan: add shrink_slab tracepoints

commit 095760730c1047c69159ce88021a7fa3833502c8 upstream.

Stable note: This patch makes later patches easier to apply but otherwise
        has little to justify it. It is a diagnostic patch that was part
        of a series addressing excessive slab shrinking after GFP_NOFS
        failures. There is detailed information on the series' motivation
        at https://lkml.org/lkml/2011/6/2/42 .

It is impossible to understand what the shrinkers are actually doing
without instrumenting the code, so add a some tracepoints to allow
insight to be gained.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Mel Gorman <mgorman@suse.de>

1 files changed, 77 insertions, 0 deletions

diff --git a/include/trace/events/vmscan.h b/include/trace/events/vmscan.h
index b2c33bd955f..36851f7f13d 100644
--- a/include/trace/events/vmscan.h
+++ b/include/trace/events/vmscan.h
@@ -179,6 +179,83 @@ DEFINE_EVENT(mm_vmscan_direct_reclaim_end_template, mm_vmscan_memcg_softlimit_re
 	TP_ARGS(nr_reclaimed)
 );
 
+TRACE_EVENT(mm_shrink_slab_start,
+	TP_PROTO(struct shrinker *shr, struct shrink_control *sc,
+		long nr_objects_to_shrink, unsigned long pgs_scanned,
+		unsigned long lru_pgs, unsigned long cache_items,
+		unsigned long long delta, unsigned long total_scan),
+
+	TP_ARGS(shr, sc, nr_objects_to_shrink, pgs_scanned, lru_pgs,
+		cache_items, delta, total_scan),
+
+	TP_STRUCT__entry(
+		__field(struct shrinker *, shr)
+		__field(void *, shrink)
+		__field(long, nr_objects_to_shrink)
+		__field(gfp_t, gfp_flags)
+		__field(unsigned long, pgs_scanned)
+		__field(unsigned long, lru_pgs)
+		__field(unsigned long, cache_items)
+		__field(unsigned long long, delta)
+		__field(unsigned long, total_scan)
+	),
+
+	TP_fast_assign(
+		__entry->shr = shr;
+		__entry->shrink = shr->shrink;
+		__entry->nr_objects_to_shrink = nr_objects_to_shrink;
+		__entry->gfp_flags = sc->gfp_mask;
+		__entry->pgs_scanned = pgs_scanned;
+		__entry->lru_pgs = lru_pgs;
+		__entry->cache_items = cache_items;
+		__entry->delta = delta;
+		__entry->total_scan = total_scan;
+	),
+
+	TP_printk("%pF %p: objects to shrink %ld gfp_flags %s pgs_scanned %ld lru_pgs %ld cache items %ld delta %lld total_scan %ld",
+		__entry->shrink,
+		__entry->shr,
+		__entry->nr_objects_to_shrink,
+		show_gfp_flags(__entry->gfp_flags),
+		__entry->pgs_scanned,
+		__entry->lru_pgs,
+		__entry->cache_items,
+		__entry->delta,
+		__entry->total_scan)
+);
+
+TRACE_EVENT(mm_shrink_slab_end,
+	TP_PROTO(struct shrinker *shr, int shrinker_retval,
+		long unused_scan_cnt, long new_scan_cnt),
+
+	TP_ARGS(shr, shrinker_retval, unused_scan_cnt, new_scan_cnt),
+
+	TP_STRUCT__entry(
+		__field(struct shrinker *, shr)
+		__field(void *, shrink)
+		__field(long, unused_scan)
+		__field(long, new_scan)
+		__field(int, retval)
+		__field(long, total_scan)
+	),
+
+	TP_fast_assign(
+		__entry->shr = shr;
+		__entry->shrink = shr->shrink;
+		__entry->unused_scan = unused_scan_cnt;
+		__entry->new_scan = new_scan_cnt;
+		__entry->retval = shrinker_retval;
+		__entry->total_scan = new_scan_cnt - unused_scan_cnt;
+	),
+
+	TP_printk("%pF %p: unused scan count %ld new scan count %ld total_scan %ld last shrinker return val %d",
+		__entry->shrink,
+		__entry->shr,
+		__entry->unused_scan,
+		__entry->new_scan,
+		__entry->total_scan,
+		__entry->retval)
+);
 
 DECLARE_EVENT_CLASS(mm_vmscan_lru_isolate_template,