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>

diff --git a/include/trace/events/vmscan.h b/include/trace/events/vmscan.h
index b2c33bd955faa4536082e62e6c9f17946994afde..36851f7f13daf558107d0df16052f5d8939bd1d1 100644 (file)
--- 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,
 

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 6b0f8a60ca68c640a1c153a5969340fb0da88151..abc798167cf249753b92874ac12838daba2292a0 100644 (file)
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -250,6 +250,7 @@ unsigned long shrink_slab(struct shrink_control *shrink,
                unsigned long long delta;
                unsigned long total_scan;
                unsigned long max_pass;
+               int shrink_ret = 0;
 
                max_pass = do_shrinker_shrink(shrinker, shrink, 0);
                delta = (4 * nr_pages_scanned) / shrinker->seeks;
@@ -274,9 +275,12 @@ unsigned long shrink_slab(struct shrink_control *shrink,
                total_scan = shrinker->nr;
                shrinker->nr = 0;
 
+               trace_mm_shrink_slab_start(shrinker, shrink, total_scan,
+                                       nr_pages_scanned, lru_pages,
+                                       max_pass, delta, total_scan);
+
                while (total_scan >= SHRINK_BATCH) {
                        long this_scan = SHRINK_BATCH;
-                       int shrink_ret;
                        int nr_before;
 
                        nr_before = do_shrinker_shrink(shrinker, shrink, 0);
@@ -293,6 +297,8 @@ unsigned long shrink_slab(struct shrink_control *shrink,
                }
 
                shrinker->nr += total_scan;
+               trace_mm_shrink_slab_end(shrinker, shrink_ret, total_scan,
+                                        shrinker->nr);
        }
        up_read(&shrinker_rwsem);
 out: