target/linux/generic/backport-5.15/020-v6.3-24-mm-multi-gen-LRU-remove-aging-fairness-safeguard.patch

   1 From e20b7386fccc18c791796eb1dc1a91eee3ccf801 Mon Sep 17 00:00:00 2001
   2 From: Yu Zhao <yuzhao@google.com>
   3 Date: Wed, 21 Dec 2022 21:19:02 -0700
   4 Subject: [PATCH 24/29] mm: multi-gen LRU: remove aging fairness safeguard
   5
   6 Recall that the aging produces the youngest generation: first it scans
   7 for accessed pages and updates their gen counters; then it increments
   8 lrugen->max_seq.
   9
  10 The current aging fairness safeguard for kswapd uses two passes to
  11 ensure the fairness to multiple eligible memcgs. On the first pass,
  12 which is shared with the eviction, it checks whether all eligible
  13 memcgs are low on cold pages. If so, it requires a second pass, on
  14 which it ages all those memcgs at the same time.
  15
  16 With memcg LRU, the aging, while ensuring eventual fairness, will run
  17 when necessary. Therefore the current aging fairness safeguard for
  18 kswapd will not be needed.
  19
  20 Note that memcg LRU only applies to global reclaim. For memcg reclaim,
  21 the aging can be unfair to different memcgs, i.e., their
  22 lrugen->max_seq can be incremented at different paces.
  23
  24 Link: https://lkml.kernel.org/r/20221222041905.2431096-5-yuzhao@google.com
  25 Signed-off-by: Yu Zhao <yuzhao@google.com>
  26 Cc: Johannes Weiner <hannes@cmpxchg.org>
  27 Cc: Jonathan Corbet <corbet@lwn.net>
  28 Cc: Michael Larabel <Michael@MichaelLarabel.com>
  29 Cc: Michal Hocko <mhocko@kernel.org>
  30 Cc: Mike Rapoport <rppt@kernel.org>
  31 Cc: Roman Gushchin <roman.gushchin@linux.dev>
  32 Cc: Suren Baghdasaryan <surenb@google.com>
  33 Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
  34 ---
  35  mm/vmscan.c | 126 ++++++++++++++++++++++++----------------------------
  36  1 file changed, 59 insertions(+), 67 deletions(-)
  37
  38 --- a/mm/vmscan.c
  39 +++ b/mm/vmscan.c
  40 @@ -131,7 +131,6 @@ struct scan_control {
  41
  42  #ifdef CONFIG_LRU_GEN
  43         /* help kswapd make better choices among multiple memcgs */
  44 -       unsigned int memcgs_need_aging:1;
  45         unsigned long last_reclaimed;
  46  #endif
  47
  48 @@ -4184,7 +4183,7 @@ done:
  49         return true;
  50  }
  51
  52 -static bool should_run_aging(struct lruvec *lruvec, unsigned long max_seq, unsigned long *min_seq,
  53 +static bool should_run_aging(struct lruvec *lruvec, unsigned long max_seq,
  54                              struct scan_control *sc, bool can_swap, unsigned long *nr_to_scan)
  55  {
  56         int gen, type, zone;
  57 @@ -4193,6 +4192,13 @@ static bool should_run_aging(struct lruv
  58         unsigned long total = 0;
  59         struct lru_gen_page *lrugen = &lruvec->lrugen;
  60         struct mem_cgroup *memcg = lruvec_memcg(lruvec);
  61 +       DEFINE_MIN_SEQ(lruvec);
  62 +
  63 +       /* whether this lruvec is completely out of cold pages */
  64 +       if (min_seq[!can_swap] + MIN_NR_GENS > max_seq) {
  65 +               *nr_to_scan = 0;
  66 +               return true;
  67 +       }
  68
  69         for (type = !can_swap; type < ANON_AND_FILE; type++) {
  70                 unsigned long seq;
  71 @@ -4221,8 +4227,6 @@ static bool should_run_aging(struct lruv
  72          * stalls when the number of generations reaches MIN_NR_GENS. Hence, the
  73          * ideal number of generations is MIN_NR_GENS+1.
  74          */
  75 -       if (min_seq[!can_swap] + MIN_NR_GENS > max_seq)
  76 -               return true;
  77         if (min_seq[!can_swap] + MIN_NR_GENS < max_seq)
  78                 return false;
  79
  80 @@ -4241,40 +4245,54 @@ static bool should_run_aging(struct lruv
  81         return false;
  82  }
  83
  84 -static bool age_lruvec(struct lruvec *lruvec, struct scan_control *sc, unsigned long min_ttl)
  85 +static bool lruvec_is_sizable(struct lruvec *lruvec, struct scan_control *sc)
  86  {
  87 -       bool need_aging;
  88 -       unsigned long nr_to_scan;
  89 -       int swappiness = get_swappiness(lruvec, sc);
  90 +       int gen, type, zone;
  91 +       unsigned long total = 0;
  92 +       bool can_swap = get_swappiness(lruvec, sc);
  93 +       struct lru_gen_page *lrugen = &lruvec->lrugen;
  94         struct mem_cgroup *memcg = lruvec_memcg(lruvec);
  95         DEFINE_MAX_SEQ(lruvec);
  96         DEFINE_MIN_SEQ(lruvec);
  97
  98 -       VM_WARN_ON_ONCE(sc->memcg_low_reclaim);
  99 +       for (type = !can_swap; type < ANON_AND_FILE; type++) {
 100 +               unsigned long seq;
 101
 102 -       mem_cgroup_calculate_protection(NULL, memcg);
 103 +               for (seq = min_seq[type]; seq <= max_seq; seq++) {
 104 +                       gen = lru_gen_from_seq(seq);
 105
 106 -       if (mem_cgroup_below_min(memcg))
 107 -               return false;
 108 +                       for (zone = 0; zone < MAX_NR_ZONES; zone++)
 109 +                               total += max(READ_ONCE(lrugen->nr_pages[gen][type][zone]), 0L);
 110 +               }
 111 +       }
 112
 113 -       need_aging = should_run_aging(lruvec, max_seq, min_seq, sc, swappiness, &nr_to_scan);
 114 +       /* whether the size is big enough to be helpful */
 115 +       return mem_cgroup_online(memcg) ? (total >> sc->priority) : total;
 116 +}
 117
 118 -       if (min_ttl) {
 119 -               int gen = lru_gen_from_seq(min_seq[LRU_GEN_FILE]);
 120 -               unsigned long birth = READ_ONCE(lruvec->lrugen.timestamps[gen]);
 121 +static bool lruvec_is_reclaimable(struct lruvec *lruvec, struct scan_control *sc,
 122 +                                 unsigned long min_ttl)
 123 +{
 124 +       int gen;
 125 +       unsigned long birth;
 126 +       struct mem_cgroup *memcg = lruvec_memcg(lruvec);
 127 +       DEFINE_MIN_SEQ(lruvec);
 128
 129 -               if (time_is_after_jiffies(birth + min_ttl))
 130 -                       return false;
 131 +       VM_WARN_ON_ONCE(sc->memcg_low_reclaim);
 132
 133 -               /* the size is likely too small to be helpful */
 134 -               if (!nr_to_scan && sc->priority != DEF_PRIORITY)
 135 -                       return false;
 136 -       }
 137 +       /* see the comment on lru_gen_page */
 138 +       gen = lru_gen_from_seq(min_seq[LRU_GEN_FILE]);
 139 +       birth = READ_ONCE(lruvec->lrugen.timestamps[gen]);
 140
 141 -       if (need_aging)
 142 -               try_to_inc_max_seq(lruvec, max_seq, sc, swappiness, false);
 143 +       if (time_is_after_jiffies(birth + min_ttl))
 144 +               return false;
 145
 146 -       return true;
 147 +       if (!lruvec_is_sizable(lruvec, sc))
 148 +               return false;
 149 +
 150 +       mem_cgroup_calculate_protection(NULL, memcg);
 151 +
 152 +       return !mem_cgroup_below_min(memcg);
 153  }
 154
 155  /* to protect the working set of the last N jiffies */
 156 @@ -4283,46 +4301,32 @@ static unsigned long lru_gen_min_ttl __r
 157  static void lru_gen_age_node(struct pglist_data *pgdat, struct scan_control *sc)
 158  {
 159         struct mem_cgroup *memcg;
 160 -       bool success = false;
 161         unsigned long min_ttl = READ_ONCE(lru_gen_min_ttl);
 162
 163         VM_WARN_ON_ONCE(!current_is_kswapd());
 164
 165         sc->last_reclaimed = sc->nr_reclaimed;
 166
 167 -       /*
 168 -        * To reduce the chance of going into the aging path, which can be
 169 -        * costly, optimistically skip it if the flag below was cleared in the
 170 -        * eviction path. This improves the overall performance when multiple
 171 -        * memcgs are available.
 172 -        */
 173 -       if (!sc->memcgs_need_aging) {
 174 -               sc->memcgs_need_aging = true;
 175 +       /* check the order to exclude compaction-induced reclaim */
 176 +       if (!min_ttl || sc->order || sc->priority == DEF_PRIORITY)
 177                 return;
 178 -       }
 179 -
 180 -       set_mm_walk(pgdat);
 181
 182         memcg = mem_cgroup_iter(NULL, NULL, NULL);
 183         do {
 184                 struct lruvec *lruvec = mem_cgroup_lruvec(memcg, pgdat);
 185
 186 -               if (age_lruvec(lruvec, sc, min_ttl))
 187 -                       success = true;
 188 +               if (lruvec_is_reclaimable(lruvec, sc, min_ttl)) {
 189 +                       mem_cgroup_iter_break(NULL, memcg);
 190 +                       return;
 191 +               }
 192
 193                 cond_resched();
 194         } while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)));
 195
 196 -       clear_mm_walk();
 197 -
 198 -       /* check the order to exclude compaction-induced reclaim */
 199 -       if (success || !min_ttl || sc->order)
 200 -               return;
 201 -
 202         /*
 203          * The main goal is to OOM kill if every generation from all memcgs is
 204          * younger than min_ttl. However, another possibility is all memcgs are
 205 -        * either below min or empty.
 206 +        * either too small or below min.
 207          */
 208         if (mutex_trylock(&oom_lock)) {
 209                 struct oom_control oc = {
 210 @@ -4830,33 +4834,27 @@ retry:
 211   *    reclaim.
 212   */
 213  static unsigned long get_nr_to_scan(struct lruvec *lruvec, struct scan_control *sc,
 214 -                                   bool can_swap, bool *need_aging)
 215 +                                   bool can_swap)
 216  {
 217         unsigned long nr_to_scan;
 218         struct mem_cgroup *memcg = lruvec_memcg(lruvec);
 219         DEFINE_MAX_SEQ(lruvec);
 220 -       DEFINE_MIN_SEQ(lruvec);
 221
 222         if (mem_cgroup_below_min(memcg) ||
 223             (mem_cgroup_below_low(memcg) && !sc->memcg_low_reclaim))
 224                 return 0;
 225
 226 -       *need_aging = should_run_aging(lruvec, max_seq, min_seq, sc, can_swap, &nr_to_scan);
 227 -       if (!*need_aging)
 228 +       if (!should_run_aging(lruvec, max_seq, sc, can_swap, &nr_to_scan))
 229                 return nr_to_scan;
 230
 231         /* skip the aging path at the default priority */
 232         if (sc->priority == DEF_PRIORITY)
 233 -               goto done;
 234 +               return nr_to_scan;
 235
 236 -       /* leave the work to lru_gen_age_node() */
 237 -       if (current_is_kswapd())
 238 -               return 0;
 239 +       try_to_inc_max_seq(lruvec, max_seq, sc, can_swap, false);
 240
 241 -       if (try_to_inc_max_seq(lruvec, max_seq, sc, can_swap, false))
 242 -               return nr_to_scan;
 243 -done:
 244 -       return min_seq[!can_swap] + MIN_NR_GENS <= max_seq ? nr_to_scan : 0;
 245 +       /* skip this lruvec as it's low on cold pages */
 246 +       return 0;
 247  }
 248
 249  static unsigned long get_nr_to_reclaim(struct scan_control *sc)
 250 @@ -4875,9 +4873,7 @@ static unsigned long get_nr_to_reclaim(s
 251  static void lru_gen_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
 252  {
 253         struct blk_plug plug;
 254 -       bool need_aging = false;
 255         unsigned long scanned = 0;
 256 -       unsigned long reclaimed = sc->nr_reclaimed;
 257         unsigned long nr_to_reclaim = get_nr_to_reclaim(sc);
 258
 259         lru_add_drain();
 260 @@ -4898,13 +4894,13 @@ static void lru_gen_shrink_lruvec(struct
 261                 else
 262                         swappiness = 0;
 263
 264 -               nr_to_scan = get_nr_to_scan(lruvec, sc, swappiness, &need_aging);
 265 +               nr_to_scan = get_nr_to_scan(lruvec, sc, swappiness);
 266                 if (!nr_to_scan)
 267 -                       goto done;
 268 +                       break;
 269
 270                 delta = evict_pages(lruvec, sc, swappiness);
 271                 if (!delta)
 272 -                       goto done;
 273 +                       break;
 274
 275                 scanned += delta;
 276                 if (scanned >= nr_to_scan)
 277 @@ -4916,10 +4912,6 @@ static void lru_gen_shrink_lruvec(struct
 278                 cond_resched();
 279         }
 280
 281 -       /* see the comment in lru_gen_age_node() */
 282 -       if (sc->nr_reclaimed - reclaimed >= MIN_LRU_BATCH && !need_aging)
 283 -               sc->memcgs_need_aging = false;
 284 -done:
 285         clear_mm_walk();
 286
 287         blk_finish_plug(&plug);