From 14f9a7a15f3d1af351f30e0438fd747b7ac253b0 Mon Sep 17 00:00:00 2001 From: Yu Zhao Date: Wed, 21 Dec 2022 21:19:01 -0700 Subject: [PATCH 03/19] UPSTREAM: mm: multi-gen LRU: remove eviction fairness safeguard Recall that the eviction consumes the oldest generation: first it bucket-sorts folios whose gen counters were updated by the aging and reclaims the rest; then it increments lrugen->min_seq. The current eviction fairness safeguard for global reclaim has a dilemma: when there are multiple eligible memcgs, should it continue or stop upon meeting the reclaim goal? If it continues, it overshoots and increases direct reclaim latency; if it stops, it loses fairness between memcgs it has taken memory away from and those it has yet to. With memcg LRU, the eviction, while ensuring eventual fairness, will stop upon meeting its goal. Therefore the current eviction fairness safeguard for global reclaim will not be needed. Note that memcg LRU only applies to global reclaim. For memcg reclaim, the eviction will continue, even if it is overshooting. This becomes unconditional due to code simplification. Link: https://lkml.kernel.org/r/20221222041905.2431096-4-yuzhao@google.com Signed-off-by: Yu Zhao Cc: Johannes Weiner Cc: Jonathan Corbet Cc: Michael Larabel Cc: Michal Hocko Cc: Mike Rapoport Cc: Roman Gushchin Cc: Suren Baghdasaryan Signed-off-by: Andrew Morton Bug: 274865848 (cherry picked from commit a579086c99ed70cc4bfc104348dbe3dd8f2787e6) Change-Id: I08ac1b3c90e29cafd0566785aaa4bcdb5db7d22c Signed-off-by: T.J. Mercier --- mm/vmscan.c | 81 +++++++++++++++-------------------------------------- 1 file changed, 23 insertions(+), 58 deletions(-) --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -448,6 +448,11 @@ static bool cgroup_reclaim(struct scan_c return sc->target_mem_cgroup; } +static bool global_reclaim(struct scan_control *sc) +{ + return !sc->target_mem_cgroup || mem_cgroup_is_root(sc->target_mem_cgroup); +} + /** * writeback_throttling_sane - is the usual dirty throttling mechanism available? * @sc: scan_control in question @@ -498,6 +503,11 @@ static bool cgroup_reclaim(struct scan_c return false; } +static bool global_reclaim(struct scan_control *sc) +{ + return true; +} + static bool writeback_throttling_sane(struct scan_control *sc) { return true; @@ -4993,8 +5003,7 @@ static int isolate_folios(struct lruvec return scanned; } -static int evict_folios(struct lruvec *lruvec, struct scan_control *sc, int swappiness, - bool *need_swapping) +static int evict_folios(struct lruvec *lruvec, struct scan_control *sc, int swappiness) { int type; int scanned; @@ -5083,9 +5092,6 @@ retry: goto retry; } - if (need_swapping && type == LRU_GEN_ANON) - *need_swapping = true; - return scanned; } @@ -5124,67 +5130,26 @@ done: return min_seq[!can_swap] + MIN_NR_GENS <= max_seq ? nr_to_scan : 0; } -static bool should_abort_scan(struct lruvec *lruvec, unsigned long seq, - struct scan_control *sc, bool need_swapping) +static unsigned long get_nr_to_reclaim(struct scan_control *sc) { - int i; - DEFINE_MAX_SEQ(lruvec); - - if (!current_is_kswapd()) { - /* age each memcg at most once to ensure fairness */ - if (max_seq - seq > 1) - return true; - - /* over-swapping can increase allocation latency */ - if (sc->nr_reclaimed >= sc->nr_to_reclaim && need_swapping) - return true; - - /* give this thread a chance to exit and free its memory */ - if (fatal_signal_pending(current)) { - sc->nr_reclaimed += MIN_LRU_BATCH; - return true; - } - - if (cgroup_reclaim(sc)) - return false; - } else if (sc->nr_reclaimed - sc->last_reclaimed < sc->nr_to_reclaim) - return false; - - /* keep scanning at low priorities to ensure fairness */ - if (sc->priority > DEF_PRIORITY - 2) - return false; - - /* - * A minimum amount of work was done under global memory pressure. For - * kswapd, it may be overshooting. For direct reclaim, the allocation - * may succeed if all suitable zones are somewhat safe. In either case, - * it's better to stop now, and restart later if necessary. - */ - for (i = 0; i <= sc->reclaim_idx; i++) { - unsigned long wmark; - struct zone *zone = lruvec_pgdat(lruvec)->node_zones + i; - - if (!managed_zone(zone)) - continue; - - wmark = current_is_kswapd() ? high_wmark_pages(zone) : low_wmark_pages(zone); - if (wmark > zone_page_state(zone, NR_FREE_PAGES)) - return false; - } + /* don't abort memcg reclaim to ensure fairness */ + if (!global_reclaim(sc)) + return -1; - sc->nr_reclaimed += MIN_LRU_BATCH; + /* discount the previous progress for kswapd */ + if (current_is_kswapd()) + return sc->nr_to_reclaim + sc->last_reclaimed; - return true; + return max(sc->nr_to_reclaim, compact_gap(sc->order)); } static void lru_gen_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc) { struct blk_plug plug; bool need_aging = false; - bool need_swapping = false; unsigned long scanned = 0; unsigned long reclaimed = sc->nr_reclaimed; - DEFINE_MAX_SEQ(lruvec); + unsigned long nr_to_reclaim = get_nr_to_reclaim(sc); lru_add_drain(); @@ -5208,7 +5173,7 @@ static void lru_gen_shrink_lruvec(struct if (!nr_to_scan) goto done; - delta = evict_folios(lruvec, sc, swappiness, &need_swapping); + delta = evict_folios(lruvec, sc, swappiness); if (!delta) goto done; @@ -5216,7 +5181,7 @@ static void lru_gen_shrink_lruvec(struct if (scanned >= nr_to_scan) break; - if (should_abort_scan(lruvec, max_seq, sc, need_swapping)) + if (sc->nr_reclaimed >= nr_to_reclaim) break; cond_resched(); @@ -5666,7 +5631,7 @@ static int run_eviction(struct lruvec *l if (sc->nr_reclaimed >= nr_to_reclaim) return 0; - if (!evict_folios(lruvec, sc, swappiness, NULL)) + if (!evict_folios(lruvec, sc, swappiness)) return 0; cond_resched();