Re: [PATCH 03/10] staging: lustre: lu_object: discard extra lru count.

From: Dilger, Andreas
Date: Tue May 01 2018 - 00:20:11 EST


On Apr 30, 2018, at 21:52, NeilBrown <neilb@xxxxxxxx> wrote:
>
> lu_object maintains 2 lru counts.
> One is a per-bucket lsb_lru_len.
> The other is the per-cpu ls_lru_len_counter.
>
> The only times the per-bucket counters are use are:
> - a debug message when an object is added
> - in lu_site_stats_get when all the counters are combined.
>
> The debug message is not essential, and the per-cpu counter
> can be used to get the combined total.
>
> So discard the per-bucket lsb_lru_len.
>
> Signed-off-by: NeilBrown <neilb@xxxxxxxx>

Looks reasonable, though it would also be possible to fix the percpu
functions rather than adding a workaround in this code.

Reviewed-by: Andreas Dilger <andreas.dilger@xxxxxxxxx>

> ---
> drivers/staging/lustre/lustre/obdclass/lu_object.c | 24 ++++++++------------
> 1 file changed, 9 insertions(+), 15 deletions(-)
>
> diff --git a/drivers/staging/lustre/lustre/obdclass/lu_object.c b/drivers/staging/lustre/lustre/obdclass/lu_object.c
> index 2a8a25d6edb5..2bf089817157 100644
> --- a/drivers/staging/lustre/lustre/obdclass/lu_object.c
> +++ b/drivers/staging/lustre/lustre/obdclass/lu_object.c
> @@ -57,10 +57,6 @@
> #include <linux/list.h>
>
> struct lu_site_bkt_data {
> - /**
> - * number of object in this bucket on the lsb_lru list.
> - */
> - long lsb_lru_len;
> /**
> * LRU list, updated on each access to object. Protected by
> * bucket lock of lu_site::ls_obj_hash.
> @@ -187,10 +183,9 @@ void lu_object_put(const struct lu_env *env, struct lu_object *o)
> if (!lu_object_is_dying(top)) {
> LASSERT(list_empty(&top->loh_lru));
> list_add_tail(&top->loh_lru, &bkt->lsb_lru);
> - bkt->lsb_lru_len++;
> percpu_counter_inc(&site->ls_lru_len_counter);
> - CDEBUG(D_INODE, "Add %p to site lru. hash: %p, bkt: %p, lru_len: %ld\n",
> - o, site->ls_obj_hash, bkt, bkt->lsb_lru_len);
> + CDEBUG(D_INODE, "Add %p to site lru. hash: %p, bkt: %p\n",
> + o, site->ls_obj_hash, bkt);
> cfs_hash_bd_unlock(site->ls_obj_hash, &bd, 1);
> return;
> }
> @@ -238,7 +233,6 @@ void lu_object_unhash(const struct lu_env *env, struct lu_object *o)
>
> list_del_init(&top->loh_lru);
> bkt = cfs_hash_bd_extra_get(obj_hash, &bd);
> - bkt->lsb_lru_len--;
> percpu_counter_dec(&site->ls_lru_len_counter);
> }
> cfs_hash_bd_del_locked(obj_hash, &bd, &top->loh_hash);
> @@ -422,7 +416,6 @@ int lu_site_purge_objects(const struct lu_env *env, struct lu_site *s,
> cfs_hash_bd_del_locked(s->ls_obj_hash,
> &bd2, &h->loh_hash);
> list_move(&h->loh_lru, &dispose);
> - bkt->lsb_lru_len--;
> percpu_counter_dec(&s->ls_lru_len_counter);
> if (did_sth == 0)
> did_sth = 1;
> @@ -621,7 +614,6 @@ static struct lu_object *htable_lookup(struct lu_site *s,
> lprocfs_counter_incr(s->ls_stats, LU_SS_CACHE_HIT);
> if (!list_empty(&h->loh_lru)) {
> list_del_init(&h->loh_lru);
> - bkt->lsb_lru_len--;
> percpu_counter_dec(&s->ls_lru_len_counter);
> }
> return lu_object_top(h);
> @@ -1834,19 +1826,21 @@ struct lu_site_stats {
> unsigned int lss_busy;
> };
>
> -static void lu_site_stats_get(struct cfs_hash *hs,
> +static void lu_site_stats_get(const struct lu_site *s,
> struct lu_site_stats *stats, int populated)
> {
> + struct cfs_hash *hs = s->ls_obj_hash;
> struct cfs_hash_bd bd;
> unsigned int i;
> + /* percpu_counter_read_positive() won't accept a const pointer */
> + struct lu_site *s2 = (struct lu_site *)s;

It would seem worthwhile to change the percpu_counter_read_positive() and
percpu_counter_read() arguments to be "const struct percpu_counter *fbc",
rather than doing this cast here. I can't see any reason that would be bad,
since both implementations just access fbc->count, and do not modify anything.

> + stats->lss_busy += cfs_hash_size_get(hs) -
> + percpu_counter_read_positive(&s2->ls_lru_len_counter);
> cfs_hash_for_each_bucket(hs, &bd, i) {
> - struct lu_site_bkt_data *bkt = cfs_hash_bd_extra_get(hs, &bd);
> struct hlist_head *hhead;
>
> cfs_hash_bd_lock(hs, &bd, 1);
> - stats->lss_busy +=
> - cfs_hash_bd_count_get(&bd) - bkt->lsb_lru_len;
> stats->lss_total += cfs_hash_bd_count_get(&bd);
> stats->lss_max_search = max((int)stats->lss_max_search,
> cfs_hash_bd_depmax_get(&bd));
> @@ -2039,7 +2033,7 @@ int lu_site_stats_print(const struct lu_site *s, struct seq_file *m)
> struct lu_site_stats stats;
>
> memset(&stats, 0, sizeof(stats));
> - lu_site_stats_get(s->ls_obj_hash, &stats, 1);
> + lu_site_stats_get(s, &stats, 1);
>
> seq_printf(m, "%d/%d %d/%ld %d %d %d %d %d %d %d\n",
> stats.lss_busy,
>
>

Cheers, Andreas
--
Andreas Dilger
Lustre Principal Architect
Intel Corporation