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Message-ID: <87k1skffjw.fsf@notabene.neil.brown.name>
Date: Fri, 04 May 2018 10:08:35 +1000
From: NeilBrown <neilb@...e.com>
To: "Dilger\, Andreas" <andreas.dilger@...el.com>
Cc: "Drokin\, Oleg" <oleg.drokin@...el.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
James Simmons <jsimmons@...radead.org>,
"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
Lustre Development List <lustre-devel@...ts.lustre.org>
Subject: Re: [PATCH 03/10] staging: lustre: lu_object: discard extra lru count.
On Tue, May 01 2018, Dilger, Andreas wrote:
> On Apr 30, 2018, at 21:52, NeilBrown <neilb@...e.com> 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@...e.com>
>
> Looks reasonable, though it would also be possible to fix the percpu
> functions rather than adding a workaround in this code.
It would be possibly to change percpu_counter_read_positive() to
take a const (and we should), but thanks to you highlighting this
I realized that I should be using percpu_counter_sum_positive(),
to read across all per-cpu counters. That takes a spinlock
so it would be a much harder sell to get it to accept a
const pointer.
Thanks,
NeilBrown
>
> Reviewed-by: Andreas Dilger <andreas.dilger@...ger.ca>
>
>> ---
>> 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
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