[PATCH 06/34] vmscan: add shrink_slab tracepoints

Mel Gorman
2012-07-23T13:46:46Z

From: Dave Chinner <dchinner@redhat.com>

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>
---
include/trace/events/vmscan.h | 77 +++++++++++++++++++++++++++++++++++++++++
mm/vmscan.c | 8 ++++-
2 files changed, 84 insertions(+), 1 deletion(-)

diff --git a/include/trace/events/vmscan.h b/include/trace/events/vmscan.h
index b2c33bd..36851f7 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,

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 72340b84..d875058 100644
--- 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:
--
1.7.9.2