On Tue, 12 Dec 2023 22:33:29 -0800
Bixuan Cui <cuibixuan@xxxxxxxx> wrote:
> From: cuibixuan <cuibixuan@xxxxxxxx>
>
> do_shrink_slab() calculates the freeable memory through shrinker->count_objects(),
> and then reclaims the memory through shrinker->scan_objects(). When reclaiming
> memory, shrinker->count_objects() takes a certain amount of time:
>
> Fun spend(us)
> ext4_es_count 4302
> ext4_es_scan 12
> super_cache_count 4195
> super_cache_scan 2103
>
> Therefore, adding the trace event to count_objects() can more accurately
> obtain the time taken for slab memory recycling.
>
> Example of output:
> kswapd0-103 [003] ..... 1098.317942: mm_shrink_count_start: kfree_rcu_shrink_count.cfi_jt+0x0/0x8 00000000c540ff51: nid: 0
> kswapd0-103 [003] ..... 1098.317951: mm_shrink_count_end: kfree_rcu_shrink_count.cfi_jt+0x0/0x8 00000000c540ff51: nid: 0 freeable:36
>
> Signed-off-by: Bixuan Cui <cuibixuan@xxxxxxxx>
> ---
> include/trace/events/vmscan.h | 49 +++++++++++++++++++++++++++++++++++
> mm/shrinker.c | 4 +++
> 2 files changed, 53 insertions(+)
>
> diff --git a/include/trace/events/vmscan.h b/include/trace/events/vmscan.h
> index 1a488c30afa5..406faa5591c1 100644
> --- a/include/trace/events/vmscan.h
> +++ b/include/trace/events/vmscan.h
> @@ -196,6 +196,55 @@ DEFINE_EVENT(mm_vmscan_direct_reclaim_end_template, mm_vmscan_memcg_softlimit_re
> );
> #endif /* CONFIG_MEMCG */
>
> +TRACE_EVENT(mm_shrink_count_start,
> + TP_PROTO(struct shrinker *shr, struct shrink_control *sc),
> +
> + TP_ARGS(shr, sc),
> +
> + TP_STRUCT__entry(
> + __field(struct shrinker *, shr)
> + __field(void *, shrink)
> + __field(int, nid)
> + ),
> +
> + TP_fast_assign(
> + __entry->shr = shr;
> + __entry->shrink = shr->count_objects;
> + __entry->nid = sc->nid;
> + ),
> +
> + TP_printk("%pS %p: nid: %d",
> + __entry->shrink,
> + __entry->shr,
> + __entry->nid)
> +);
> +
> +TRACE_EVENT(mm_shrink_count_end,
> + TP_PROTO(struct shrinker *shr, struct shrink_control *sc, long freeable),
> +
> + TP_ARGS(shr, sc, freeable),
> +
> + TP_STRUCT__entry(
> + __field(struct shrinker *, shr)
> + __field(void *, shrink)
> + __field(int, nid)
int : 4 bytes
> + __field(long, freeable)
long: 8 bytes
You may want to swap the above, otherwise you added a hole in the trace
event. The compiler will add 4 bytes of padding between 'nid' and
'freeable'. That is, if you change it to:
TP_STRUCT__entry(
__field(struct shrinker *, shr)
__field(void *, shrink)
__field(long, freeable)
__field(int, nid)
You will save 4 bytes per event in the ring buffer.
-- Steve
> + ),
> +
> + TP_fast_assign(
> + __entry->shr = shr;
> + __entry->shrink = shr->count_objects;
> + __entry->nid = sc->nid;
> + __entry->freeable = freeable;
> + ),
> +
> + TP_printk("%pS %p: nid: %d freeable:%ld",
> + __entry->shrink,
> + __entry->shr,
> + __entry->nid,
> + __entry->freeable)
> +);
> +
> TRACE_EVENT(mm_shrink_slab_start,
> TP_PROTO(struct shrinker *shr, struct shrink_control *sc,
> long nr_objects_to_shrink, unsigned long cache_items,
> diff --git a/mm/shrinker.c b/mm/shrinker.c
> index dd91eab43ed3..d0c7bf61db61 100644
> --- a/mm/shrinker.c
> +++ b/mm/shrinker.c
> @@ -379,7 +379,11 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
> : SHRINK_BATCH;
> long scanned = 0, next_deferred;
>
> + trace_mm_shrink_count_start(shrinker, shrinkctl);
> +
> freeable = shrinker->count_objects(shrinker, shrinkctl);
> +
> + trace_mm_shrink_count_end(shrinker, shrinkctl, freeable);
> if (freeable == 0 || freeable == SHRINK_EMPTY)
> return freeable;
>
