Re: [PATCH 1/3] mm, lru_gen: batch update counters on againg

From: Chris Li
Date: Tue Dec 26 2023 - 18:43:57 EST

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Hi Kairui,

Some early feedback on your patch. I am still working my way through
your patches.
Might have more questions.

On Fri, Dec 22, 2023 at 2:24 AM Kairui Song <ryncsn@xxxxxxxxx> wrote:
>
> From: Kairui Song <kasong@xxxxxxxxxxx>
>
> When lru_gen is aging, it will update mm counters page by page,
> which causes a higher overhead if age happens frequently or there
> are a lot of pages in one generation getting moved.
> Optimize this by doing the counter update in batch.
>
> Although most __mod_*_state has its own caches the overhead
> is still observable.
>
> Tested in a 4G memcg on a EPYC 7K62 with:
>
> memcached -u nobody -m 16384 -s /tmp/memcached.socket \
> -a 0766 -t 16 -B binary &
>
> memtier_benchmark -S /tmp/memcached.socket \
> -P memcache_binary -n allkeys \
> --key-minimum=1 --key-maximum=16000000 -d 1024 \
> --ratio=1:0 --key-pattern=P:P -c 2 -t 16 --pipeline 8 -x 6
>
> Average result of 18 test runs:
>
> Before: 44017.78 Ops/sec
> After: 44687.08 Ops/sec (+1.5%)
>
> Signed-off-by: Kairui Song <kasong@xxxxxxxxxxx>
> ---
> mm/vmscan.c | 64 +++++++++++++++++++++++++++++++++++++++++++++--------
> 1 file changed, 55 insertions(+), 9 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index b4ca3563bcf4..e3b4797b9729 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -3095,9 +3095,47 @@ static int folio_update_gen(struct folio *folio, int gen)
> return ((old_flags & LRU_GEN_MASK) >> LRU_GEN_PGOFF) - 1;
> }
>
> +/*
> + * Update LRU gen in batch for each lru_gen LRU list. The batch is limited to
> + * each gen / type / zone level LRU. Batch is applied after finished or aborted
> + * scanning one LRU list.
> + */
> +struct gen_update_batch {
> + int delta[MAX_NR_GENS];
> +};
> +
> +static void lru_gen_update_batch(struct lruvec *lruvec, bool type, int zone,
"type" need to be int, it is either LRU_GEN_FILE or LRU_GEN_ANON.

Ideally the type is an enum that defines LRU_GEN_FILE or LRU_GEN_ANON.
bool is not the right C type of "type" here. The rest of the code uses
"int" for type as well.

I saw you use "bool type" in other patches as well. All need to change
to "int type".

Chris

> + struct gen_update_batch *batch)
> +{
> + int gen;
> + int promoted = 0;
> + struct lru_gen_folio *lrugen = &lruvec->lrugen;
> + enum lru_list lru = type ? LRU_INACTIVE_FILE : LRU_INACTIVE_ANON;
> +
> + for (gen = 0; gen < MAX_NR_GENS; gen++) {
> + int delta = batch->delta[gen];
> +
> + if (!delta)
> + continue;
> +
> + WRITE_ONCE(lrugen->nr_pages[gen][type][zone],
> + lrugen->nr_pages[gen][type][zone] + delta);
> +
> + if (lru_gen_is_active(lruvec, gen))
> + promoted += delta;
> + }
> +
> + if (promoted) {
> + __update_lru_size(lruvec, lru, zone, -promoted);
> + __update_lru_size(lruvec, lru + LRU_ACTIVE, zone, promoted);
> + }
> +}
> +
> /* protect pages accessed multiple times through file descriptors */
> -static int folio_inc_gen(struct lruvec *lruvec, struct folio *folio, bool reclaiming)
> +static int folio_inc_gen(struct lruvec *lruvec, struct folio *folio,
> + bool reclaiming, struct gen_update_batch *batch)
> {
> + int delta = folio_nr_pages(folio);
> int type = folio_is_file_lru(folio);
> struct lru_gen_folio *lrugen = &lruvec->lrugen;
> int new_gen, old_gen = lru_gen_from_seq(lrugen->min_seq[type]);
> @@ -3120,7 +3158,8 @@ static int folio_inc_gen(struct lruvec *lruvec, struct folio *folio, bool reclai
> new_flags |= BIT(PG_reclaim);
> } while (!try_cmpxchg(&folio->flags, &old_flags, new_flags));
>
> - lru_gen_update_size(lruvec, folio, old_gen, new_gen);
> + batch->delta[old_gen] -= delta;
> + batch->delta[new_gen] += delta;
>
> return new_gen;
> }
> @@ -3663,6 +3702,7 @@ static bool inc_min_seq(struct lruvec *lruvec, int type, bool can_swap)
> {
> int zone;
> int remaining = MAX_LRU_BATCH;
> + struct gen_update_batch batch = { };
> struct lru_gen_folio *lrugen = &lruvec->lrugen;
> int new_gen, old_gen = lru_gen_from_seq(lrugen->min_seq[type]);
>
> @@ -3681,12 +3721,15 @@ static bool inc_min_seq(struct lruvec *lruvec, int type, bool can_swap)
> VM_WARN_ON_ONCE_FOLIO(folio_is_file_lru(folio) != type, folio);
> VM_WARN_ON_ONCE_FOLIO(folio_zonenum(folio) != zone, folio);
>
> - new_gen = folio_inc_gen(lruvec, folio, false);
> + new_gen = folio_inc_gen(lruvec, folio, false, &batch);
> list_move_tail(&folio->lru, &lrugen->folios[new_gen][type][zone]);
>
> - if (!--remaining)
> + if (!--remaining) {
> + lru_gen_update_batch(lruvec, type, zone, &batch);
> return false;
> + }
> }
> + lru_gen_update_batch(lruvec, type, zone, &batch);
> }
> done:
> reset_ctrl_pos(lruvec, type, true);
> @@ -4197,7 +4240,7 @@ static int lru_gen_memcg_seg(struct lruvec *lruvec)
> ******************************************************************************/
>
> static bool sort_folio(struct lruvec *lruvec, struct folio *folio, struct scan_control *sc,
> - int tier_idx)
> + int tier_idx, struct gen_update_batch *batch)
> {
> bool success;
> int gen = folio_lru_gen(folio);
> @@ -4239,7 +4282,7 @@ static bool sort_folio(struct lruvec *lruvec, struct folio *folio, struct scan_c
> if (tier > tier_idx || refs == BIT(LRU_REFS_WIDTH)) {
> int hist = lru_hist_from_seq(lrugen->min_seq[type]);
>
> - gen = folio_inc_gen(lruvec, folio, false);
> + gen = folio_inc_gen(lruvec, folio, false, batch);
> list_move_tail(&folio->lru, &lrugen->folios[gen][type][zone]);
>
> WRITE_ONCE(lrugen->protected[hist][type][tier - 1],
> @@ -4249,7 +4292,7 @@ static bool sort_folio(struct lruvec *lruvec, struct folio *folio, struct scan_c
>
> /* ineligible */
> if (zone > sc->reclaim_idx || skip_cma(folio, sc)) {
> - gen = folio_inc_gen(lruvec, folio, false);
> + gen = folio_inc_gen(lruvec, folio, false, batch);
> list_move_tail(&folio->lru, &lrugen->folios[gen][type][zone]);
> return true;
> }
> @@ -4257,7 +4300,7 @@ static bool sort_folio(struct lruvec *lruvec, struct folio *folio, struct scan_c
> /* waiting for writeback */
> if (folio_test_locked(folio) || folio_test_writeback(folio) ||
> (type == LRU_GEN_FILE && folio_test_dirty(folio))) {
> - gen = folio_inc_gen(lruvec, folio, true);
> + gen = folio_inc_gen(lruvec, folio, true, batch);
> list_move(&folio->lru, &lrugen->folios[gen][type][zone]);
> return true;
> }
> @@ -4323,6 +4366,7 @@ static int scan_folios(struct lruvec *lruvec, struct scan_control *sc,
> for (i = MAX_NR_ZONES; i > 0; i--) {
> LIST_HEAD(moved);
> int skipped_zone = 0;
> + struct gen_update_batch batch = { };
> int zone = (sc->reclaim_idx + i) % MAX_NR_ZONES;
> struct list_head *head = &lrugen->folios[gen][type][zone];
>
> @@ -4337,7 +4381,7 @@ static int scan_folios(struct lruvec *lruvec, struct scan_control *sc,
>
> scanned += delta;
>
> - if (sort_folio(lruvec, folio, sc, tier))
> + if (sort_folio(lruvec, folio, sc, tier, &batch))
> sorted += delta;
> else if (isolate_folio(lruvec, folio, sc)) {
> list_add(&folio->lru, list);
> @@ -4357,6 +4401,8 @@ static int scan_folios(struct lruvec *lruvec, struct scan_control *sc,
> skipped += skipped_zone;
> }
>
> + lru_gen_update_batch(lruvec, type, zone, &batch);
> +
> if (!remaining || isolated >= MIN_LRU_BATCH)
> break;
> }
> --
> 2.43.0
>
>

Next message: Youling Tang: "[PATCH v2] kdump: Remove redundant DEFAULT_CRASH_KERNEL_LOW_SIZE"
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In reply to: Kairui Song: "Re: [PATCH 1/3] mm, lru_gen: batch update counters on againg"
Next in thread: Kairui Song: "Re: [PATCH 1/3] mm, lru_gen: batch update counters on againg"
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