RE: [PATCH RFC] mm: mglru: provide a separate list for lazyfree anon folios

From: wang wei
Date: Sat Sep 14 2024 - 21:03:17 EST

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In reply to: Barry Song: "[PATCH RFC] mm: mglru: provide a separate list for lazyfree anon folios"
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> -----Original Message-----
> From: linux-kernel+bounces-329184-a929244872=163.com@xxxxxxxxxxxxxxx
> <linux-kernel+bounces-329184-a929244872=163.com@xxxxxxxxxxxxxxx> On
> Behalf Of Barry Song
> Sent: Saturday, September 14, 2024 2:38 PM
> To: akpm@xxxxxxxxxxxxxxxxxxxx; linux-mm@xxxxxxxxx
> Cc: mhocko@xxxxxxxx; fengbaopeng@xxxxxxxxx; gaoxu2@xxxxxxxxx;
> hailong.liu@xxxxxxxx; kaleshsingh@xxxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx; lokeshgidra@xxxxxxxxxx; ngeoffray@xxxxxxxxxx;
> shli@xxxxxx; surenb@xxxxxxxxxx; yipengxiang@xxxxxxxxx;
> david@xxxxxxxxxx; yuzhao@xxxxxxxxxx; minchan@xxxxxxxxxx; Barry Song
> <v-songbaohua@xxxxxxxx>
> Subject: [PATCH RFC] mm: mglru: provide a separate list for lazyfree anon
> folios
>
> From: Barry Song <v-songbaohua@xxxxxxxx>
>
> This follows up on the discussion regarding Gaoxu's work[1]. It's unclear
if
> there's still interest in implementing a separate LRU list for lazyfree
folios, but I
> decided to explore it out of curiosity.
>
> According to Lokesh, MADV_FREE'd anon folios are expected to be released
> earlier than file folios. One option, as implemented by Gao Xu, is to
place
> lazyfree anon folios at the tail of the file's `min_seq` generation.
However, this
> approach results in lazyfree folios being released in a LIFO manner, which
> conflicts with LRU behavior, as noted by Michal.
>
> To address this, this patch proposes maintaining a separate list for
lazyfree
> anon folios while keeping them classified under the "file" LRU type to
minimize
> code changes. These lazyfree anon folios will still be counted as file
folios and
> share the same generation with regular files. In the eviction path, the
lazyfree
> list will be prioritized for scanning before the actual file LRU list.
>
> [1] https://lore.kernel.org/linux-
> mm/f29f64e29c08427b95e3df30a5770056@xxxxxxxxx/
>
> Signed-off-by: Barry Song <v-songbaohua@xxxxxxxx>
> ---
> include/linux/mm_inline.h | 5 +-
> include/linux/mmzone.h | 2 +-
> mm/vmscan.c | 97 +++++++++++++++++++++++----------------
> 3 files changed, 61 insertions(+), 43 deletions(-)
>
> diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h index
> f4fe593c1400..118d70ed3120 100644
> --- a/include/linux/mm_inline.h
> +++ b/include/linux/mm_inline.h
> @@ -225,6 +225,7 @@ static inline bool lru_gen_add_folio(struct lruvec
> *lruvec, struct folio *folio,
> int gen = folio_lru_gen(folio);
> int type = folio_is_file_lru(folio);
> int zone = folio_zonenum(folio);
> + int lazyfree = type ? folio_test_anon(folio) : 0;
> struct lru_gen_folio *lrugen = &lruvec->lrugen;
>
> VM_WARN_ON_ONCE_FOLIO(gen != -1, folio); @@ -262,9 +263,9
> @@ static inline bool lru_gen_add_folio(struct lruvec *lruvec, struct
folio
> *folio,
> lru_gen_update_size(lruvec, folio, -1, gen);
> /* for folio_rotate_reclaimable() */
> if (reclaiming)
> - list_add_tail(&folio->lru,
&lrugen->folios[gen][type][zone]);
> + list_add_tail(&folio->lru, &lrugen->folios[gen][type +
> +lazyfree][zone]);
> else
> - list_add(&folio->lru, &lrugen->folios[gen][type][zone]);
> + list_add(&folio->lru, &lrugen->folios[gen][type +
> lazyfree][zone]);
>
> return true;
> }
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index
> 17506e4a2835..5d2331778528 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -434,7 +434,7 @@ struct lru_gen_folio {
> /* the birth time of each generation in jiffies */
> unsigned long timestamps[MAX_NR_GENS];
> /* the multi-gen LRU lists, lazily sorted on eviction */
> - struct list_head
> folios[MAX_NR_GENS][ANON_AND_FILE][MAX_NR_ZONES];
> + struct list_head folios[MAX_NR_GENS][ANON_AND_FILE +
> 1][MAX_NR_ZONES];
This also divides lazy free filio into MAX_NR_ZONES generations.
The gen of a lazy free filio depends on the gen in the anno list before
it is marked as lazy free. Whether it will happen that lazy free filios
are released in an order that is not consistent with the order of the mark?

> /* the multi-gen LRU sizes, eventually consistent */
> long nr_pages[MAX_NR_GENS][ANON_AND_FILE][MAX_NR_ZONES];
> /* the exponential moving average of refaulted */ diff --git
> a/mm/vmscan.c b/mm/vmscan.c index 96abf4a52382..9dc665dc6ba9
> 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -3725,21 +3725,25 @@ static bool inc_min_seq(struct lruvec *lruvec, int
> type, bool can_swap)
>
> /* prevent cold/hot inversion if force_scan is true */
> for (zone = 0; zone < MAX_NR_ZONES; zone++) {
> - struct list_head *head = &lrugen-
> >folios[old_gen][type][zone];
> + int list_num = type ? 2 : 1;
> + struct list_head *head;
>
> - while (!list_empty(head)) {
> - struct folio *folio = lru_to_folio(head);
> + for (int i = list_num - 1; i >= 0; i--) {
> + head = &lrugen->folios[old_gen][type + i][zone];
> + while (!list_empty(head)) {
> + struct folio *folio = lru_to_folio(head);
>
> -
> VM_WARN_ON_ONCE_FOLIO(folio_test_unevictable(folio), folio);
> - VM_WARN_ON_ONCE_FOLIO(folio_test_active(folio),
> folio);
> -
> VM_WARN_ON_ONCE_FOLIO(folio_is_file_lru(folio) != type, folio);
> -
> VM_WARN_ON_ONCE_FOLIO(folio_zonenum(folio) != zone, folio);
> +
> VM_WARN_ON_ONCE_FOLIO(folio_test_unevictable(folio), folio);
> +
> VM_WARN_ON_ONCE_FOLIO(folio_test_active(folio), folio);
> +
> 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);
> - list_move_tail(&folio->lru, &lrugen-
> >folios[new_gen][type][zone]);
> + new_gen = folio_inc_gen(lruvec, folio,
false);
> + list_move_tail(&folio->lru, &lrugen-
> >folios[new_gen][type +
> +i][zone]);
>
> - if (!--remaining)
> - return false;
> + if (!--remaining)
> + return false;
> + }
> }
> }
> done:
> @@ -4291,6 +4295,7 @@ static bool sort_folio(struct lruvec *lruvec, struct
> folio *folio, struct scan_c
> int refs = folio_lru_refs(folio);
> int tier = lru_tier_from_refs(refs);
> struct lru_gen_folio *lrugen = &lruvec->lrugen;
> + int lazyfree = type ? folio_test_anon(folio) : 0;
>
> VM_WARN_ON_ONCE_FOLIO(gen >= MAX_NR_GENS, folio);
>
> @@ -4306,7 +4311,7 @@ static bool sort_folio(struct lruvec *lruvec, struct
> folio *folio, struct scan_c
>
> /* promoted */
> if (gen != lru_gen_from_seq(lrugen->min_seq[type])) {
> - list_move(&folio->lru, &lrugen->folios[gen][type][zone]);
> + list_move(&folio->lru, &lrugen->folios[gen][type +
> lazyfree][zone]);
> return true;
> }
>
> @@ -4315,7 +4320,7 @@ static bool sort_folio(struct lruvec *lruvec, struct
> folio *folio, struct scan_c
> int hist = lru_hist_from_seq(lrugen->min_seq[type]);
>
> gen = folio_inc_gen(lruvec, folio, false);
> - list_move_tail(&folio->lru,
&lrugen->folios[gen][type][zone]);
> + list_move_tail(&folio->lru, &lrugen->folios[gen][type +
> +lazyfree][zone]);
>
> WRITE_ONCE(lrugen->protected[hist][type][tier - 1],
> lrugen->protected[hist][type][tier - 1] + delta);
@@ -
> 4325,7 +4330,7 @@ static bool sort_folio(struct lruvec *lruvec, struct
folio
> *folio, struct scan_c
> /* ineligible */
> if (!folio_test_lru(folio) || zone > sc->reclaim_idx) {
> gen = folio_inc_gen(lruvec, folio, false);
> - list_move_tail(&folio->lru,
&lrugen->folios[gen][type][zone]);
> + list_move_tail(&folio->lru, &lrugen->folios[gen][type +
> +lazyfree][zone]);
> return true;
> }
>
> @@ -4333,7 +4338,7 @@ static bool sort_folio(struct lruvec *lruvec, struct
> folio *folio, struct scan_c
> if (folio_test_locked(folio) || folio_test_writeback(folio) ||
> (type == LRU_GEN_FILE && folio_test_dirty(folio))) {
> gen = folio_inc_gen(lruvec, folio, true);
> - list_move(&folio->lru, &lrugen->folios[gen][type][zone]);
> + list_move(&folio->lru, &lrugen->folios[gen][type +
> lazyfree][zone]);
> return true;
> }
>
> @@ -4377,7 +4382,7 @@ static bool isolate_folio(struct lruvec *lruvec,
struct
> folio *folio, struct sca static int scan_folios(struct lruvec *lruvec,
struct
> scan_control *sc,
> int type, int tier, struct list_head *list) {
> - int i;
> + int i, j;
> int gen;
> enum vm_event_item item;
> int sorted = 0;
> @@ -4399,33 +4404,38 @@ static int scan_folios(struct lruvec *lruvec,
struct
> scan_control *sc,
> LIST_HEAD(moved);
> int skipped_zone = 0;
> int zone = (sc->reclaim_idx + i) % MAX_NR_ZONES;
> - struct list_head *head = &lrugen->folios[gen][type][zone];
> -
> - while (!list_empty(head)) {
> - struct folio *folio = lru_to_folio(head);
> - int delta = folio_nr_pages(folio);
> -
> -
> VM_WARN_ON_ONCE_FOLIO(folio_test_unevictable(folio), folio);
> - VM_WARN_ON_ONCE_FOLIO(folio_test_active(folio),
> folio);
> -
> VM_WARN_ON_ONCE_FOLIO(folio_is_file_lru(folio) != type, folio);
> -
> VM_WARN_ON_ONCE_FOLIO(folio_zonenum(folio) != zone, folio);
> -
> - scanned += delta;
> + int list_num = type ? 2 : 1;
> + struct list_head *head;
In addition, scan_folios will also age lazy free list. Is this necessary?
> +
> + for (j = list_num - 1; j >= 0; j--) {
> + head = &lrugen->folios[gen][type + j][zone];
> + while (!list_empty(head)) {
> + struct folio *folio = lru_to_folio(head);
> + int delta = folio_nr_pages(folio);
> +
> +
> VM_WARN_ON_ONCE_FOLIO(folio_test_unevictable(folio), folio);
> +
> VM_WARN_ON_ONCE_FOLIO(folio_test_active(folio), folio);
> +
> VM_WARN_ON_ONCE_FOLIO(folio_is_file_lru(folio) != type, folio);
> +
> VM_WARN_ON_ONCE_FOLIO(folio_zonenum(folio) != zone, folio);
> +
> + scanned += delta;
> +
> + if (sort_folio(lruvec, folio, sc, tier))
> + sorted += delta;
> + else if (isolate_folio(lruvec, folio, sc)) {
> + list_add(&folio->lru, list);
> + isolated += delta;
> + } else {
> + list_move(&folio->lru, &moved);
> + skipped_zone += delta;
> + }
>
> - if (sort_folio(lruvec, folio, sc, tier))
> - sorted += delta;
> - else if (isolate_folio(lruvec, folio, sc)) {
> - list_add(&folio->lru, list);
> - isolated += delta;
> - } else {
> - list_move(&folio->lru, &moved);
> - skipped_zone += delta;
> + if (!--remaining || max(isolated,
> skipped_zone) >= MIN_LRU_BATCH)
> + goto isolate_done;
> }
> -
> - if (!--remaining || max(isolated, skipped_zone) >=
> MIN_LRU_BATCH)
> - break;
> }
>
> +isolate_done:
> if (skipped_zone) {
> list_splice(&moved, head);
> __count_zid_vm_events(PGSCAN_SKIP, zone,
> skipped_zone); @@ -5586,8 +5596,15 @@ void lru_gen_init_lruvec(struct
> lruvec *lruvec)
> for (i = 0; i <= MIN_NR_GENS + 1; i++)
> lrugen->timestamps[i] = jiffies;
>
> - for_each_gen_type_zone(gen, type, zone)
> + for_each_gen_type_zone(gen, type, zone) {
> INIT_LIST_HEAD(&lrugen->folios[gen][type][zone]);
> + /*
> + * lazyfree anon folios have a separate list while using
> + * file as type
> + */
> + if (type)
> + INIT_LIST_HEAD(&lrugen->folios[gen][type +
> 1][zone]);
> + }
>
> if (mm_state)
> mm_state->seq = MIN_NR_GENS;
> --
> 2.39.3 (Apple Git-146)

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