target/linux/generic/backport-6.1/020-v6.3-04-BACKPORT-mm-multi-gen-LRU-remove-aging-fairness-safe.patch

   1 From f3c93d2e37a3c56593d7ccf4f4bcf1b58426fdd8 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 04/19] BACKPORT: mm: multi-gen LRU: remove aging fairness
   5  safeguard
   6
   7 Recall that the aging produces the youngest generation: first it scans
   8 for accessed folios and updates their gen counters; then it increments
   9 lrugen->max_seq.
  10
  11 The current aging fairness safeguard for kswapd uses two passes to
  12 ensure the fairness to multiple eligible memcgs. On the first pass,
  13 which is shared with the eviction, it checks whether all eligible
  14 memcgs are low on cold folios. If so, it requires a second pass, on
  15 which it ages all those memcgs at the same time.
  16
  17 With memcg LRU, the aging, while ensuring eventual fairness, will run
  18 when necessary. Therefore the current aging fairness safeguard for
  19 kswapd will not be needed.
  20
  21 Note that memcg LRU only applies to global reclaim. For memcg reclaim,
  22 the aging can be unfair to different memcgs, i.e., their
  23 lrugen->max_seq can be incremented at different paces.
  24
  25 Link: https://lkml.kernel.org/r/20221222041905.2431096-5-yuzhao@google.com
  26 Signed-off-by: Yu Zhao <yuzhao@google.com>
  27 Cc: Johannes Weiner <hannes@cmpxchg.org>
  28 Cc: Jonathan Corbet <corbet@lwn.net>
  29 Cc: Michael Larabel <Michael@MichaelLarabel.com>
  30 Cc: Michal Hocko <mhocko@kernel.org>
  31 Cc: Mike Rapoport <rppt@kernel.org>
  32 Cc: Roman Gushchin <roman.gushchin@linux.dev>
  33 Cc: Suren Baghdasaryan <surenb@google.com>
  34 Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
  35 Bug: 274865848
  36 (cherry picked from commit 7348cc91821b0cb24dfb00e578047f68299a50ab)
  37 [TJ: Resolved conflicts with older function signatures for
  38 min_cgroup_below_min / min_cgroup_below_low]
  39 Change-Id: I6e36ecfbaaefbc0a56d9a9d5d7cbe404ed7f57a5
  40 Signed-off-by: T.J. Mercier <tjmercier@google.com>
  41 ---
  42  mm/vmscan.c | 126 ++++++++++++++++++++++++----------------------------
  43  1 file changed, 59 insertions(+), 67 deletions(-)
  44
  45 --- a/mm/vmscan.c
  46 +++ b/mm/vmscan.c
  47 @@ -136,7 +136,6 @@ struct scan_control {
  48
  49  #ifdef CONFIG_LRU_GEN
  50         /* help kswapd make better choices among multiple memcgs */
  51 -       unsigned int memcgs_need_aging:1;
  52         unsigned long last_reclaimed;
  53  #endif
  54
  55 @@ -4457,7 +4456,7 @@ done:
  56         return true;
  57  }
  58
  59 -static bool should_run_aging(struct lruvec *lruvec, unsigned long max_seq, unsigned long *min_seq,
  60 +static bool should_run_aging(struct lruvec *lruvec, unsigned long max_seq,
  61                              struct scan_control *sc, bool can_swap, unsigned long *nr_to_scan)
  62  {
  63         int gen, type, zone;
  64 @@ -4466,6 +4465,13 @@ static bool should_run_aging(struct lruv
  65         unsigned long total = 0;
  66         struct lru_gen_folio *lrugen = &lruvec->lrugen;
  67         struct mem_cgroup *memcg = lruvec_memcg(lruvec);
  68 +       DEFINE_MIN_SEQ(lruvec);
  69 +
  70 +       /* whether this lruvec is completely out of cold folios */
  71 +       if (min_seq[!can_swap] + MIN_NR_GENS > max_seq) {
  72 +               *nr_to_scan = 0;
  73 +               return true;
  74 +       }
  75
  76         for (type = !can_swap; type < ANON_AND_FILE; type++) {
  77                 unsigned long seq;
  78 @@ -4494,8 +4500,6 @@ static bool should_run_aging(struct lruv
  79          * stalls when the number of generations reaches MIN_NR_GENS. Hence, the
  80          * ideal number of generations is MIN_NR_GENS+1.
  81          */
  82 -       if (min_seq[!can_swap] + MIN_NR_GENS > max_seq)
  83 -               return true;
  84         if (min_seq[!can_swap] + MIN_NR_GENS < max_seq)
  85                 return false;
  86
  87 @@ -4514,40 +4518,54 @@ static bool should_run_aging(struct lruv
  88         return false;
  89  }
  90
  91 -static bool age_lruvec(struct lruvec *lruvec, struct scan_control *sc, unsigned long min_ttl)
  92 +static bool lruvec_is_sizable(struct lruvec *lruvec, struct scan_control *sc)
  93  {
  94 -       bool need_aging;
  95 -       unsigned long nr_to_scan;
  96 -       int swappiness = get_swappiness(lruvec, sc);
  97 +       int gen, type, zone;
  98 +       unsigned long total = 0;
  99 +       bool can_swap = get_swappiness(lruvec, sc);
 100 +       struct lru_gen_folio *lrugen = &lruvec->lrugen;
 101         struct mem_cgroup *memcg = lruvec_memcg(lruvec);
 102         DEFINE_MAX_SEQ(lruvec);
 103         DEFINE_MIN_SEQ(lruvec);
 104
 105 -       VM_WARN_ON_ONCE(sc->memcg_low_reclaim);
 106 +       for (type = !can_swap; type < ANON_AND_FILE; type++) {
 107 +               unsigned long seq;
 108
 109 -       mem_cgroup_calculate_protection(NULL, memcg);
 110 +               for (seq = min_seq[type]; seq <= max_seq; seq++) {
 111 +                       gen = lru_gen_from_seq(seq);
 112
 113 -       if (mem_cgroup_below_min(memcg))
 114 -               return false;
 115 +                       for (zone = 0; zone < MAX_NR_ZONES; zone++)
 116 +                               total += max(READ_ONCE(lrugen->nr_pages[gen][type][zone]), 0L);
 117 +               }
 118 +       }
 119
 120 -       need_aging = should_run_aging(lruvec, max_seq, min_seq, sc, swappiness, &nr_to_scan);
 121 +       /* whether the size is big enough to be helpful */
 122 +       return mem_cgroup_online(memcg) ? (total >> sc->priority) : total;
 123 +}
 124
 125 -       if (min_ttl) {
 126 -               int gen = lru_gen_from_seq(min_seq[LRU_GEN_FILE]);
 127 -               unsigned long birth = READ_ONCE(lruvec->lrugen.timestamps[gen]);
 128 +static bool lruvec_is_reclaimable(struct lruvec *lruvec, struct scan_control *sc,
 129 +                                 unsigned long min_ttl)
 130 +{
 131 +       int gen;
 132 +       unsigned long birth;
 133 +       struct mem_cgroup *memcg = lruvec_memcg(lruvec);
 134 +       DEFINE_MIN_SEQ(lruvec);
 135
 136 -               if (time_is_after_jiffies(birth + min_ttl))
 137 -                       return false;
 138 +       VM_WARN_ON_ONCE(sc->memcg_low_reclaim);
 139
 140 -               /* the size is likely too small to be helpful */
 141 -               if (!nr_to_scan && sc->priority != DEF_PRIORITY)
 142 -                       return false;
 143 -       }
 144 +       /* see the comment on lru_gen_folio */
 145 +       gen = lru_gen_from_seq(min_seq[LRU_GEN_FILE]);
 146 +       birth = READ_ONCE(lruvec->lrugen.timestamps[gen]);
 147
 148 -       if (need_aging)
 149 -               try_to_inc_max_seq(lruvec, max_seq, sc, swappiness, false);
 150 +       if (time_is_after_jiffies(birth + min_ttl))
 151 +               return false;
 152
 153 -       return true;
 154 +       if (!lruvec_is_sizable(lruvec, sc))
 155 +               return false;
 156 +
 157 +       mem_cgroup_calculate_protection(NULL, memcg);
 158 +
 159 +       return !mem_cgroup_below_min(memcg);
 160  }
 161
 162  /* to protect the working set of the last N jiffies */
 163 @@ -4556,46 +4574,32 @@ static unsigned long lru_gen_min_ttl __r
 164  static void lru_gen_age_node(struct pglist_data *pgdat, struct scan_control *sc)
 165  {
 166         struct mem_cgroup *memcg;
 167 -       bool success = false;
 168         unsigned long min_ttl = READ_ONCE(lru_gen_min_ttl);
 169
 170         VM_WARN_ON_ONCE(!current_is_kswapd());
 171
 172         sc->last_reclaimed = sc->nr_reclaimed;
 173
 174 -       /*
 175 -        * To reduce the chance of going into the aging path, which can be
 176 -        * costly, optimistically skip it if the flag below was cleared in the
 177 -        * eviction path. This improves the overall performance when multiple
 178 -        * memcgs are available.
 179 -        */
 180 -       if (!sc->memcgs_need_aging) {
 181 -               sc->memcgs_need_aging = true;
 182 +       /* check the order to exclude compaction-induced reclaim */
 183 +       if (!min_ttl || sc->order || sc->priority == DEF_PRIORITY)
 184                 return;
 185 -       }
 186 -
 187 -       set_mm_walk(pgdat);
 188
 189         memcg = mem_cgroup_iter(NULL, NULL, NULL);
 190         do {
 191                 struct lruvec *lruvec = mem_cgroup_lruvec(memcg, pgdat);
 192
 193 -               if (age_lruvec(lruvec, sc, min_ttl))
 194 -                       success = true;
 195 +               if (lruvec_is_reclaimable(lruvec, sc, min_ttl)) {
 196 +                       mem_cgroup_iter_break(NULL, memcg);
 197 +                       return;
 198 +               }
 199
 200                 cond_resched();
 201         } while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)));
 202
 203 -       clear_mm_walk();
 204 -
 205 -       /* check the order to exclude compaction-induced reclaim */
 206 -       if (success || !min_ttl || sc->order)
 207 -               return;
 208 -
 209         /*
 210          * The main goal is to OOM kill if every generation from all memcgs is
 211          * younger than min_ttl. However, another possibility is all memcgs are
 212 -        * either below min or empty.
 213 +        * either too small or below min.
 214          */
 215         if (mutex_trylock(&oom_lock)) {
 216                 struct oom_control oc = {
 217 @@ -5113,33 +5117,27 @@ retry:
 218   *    reclaim.
 219   */
 220  static unsigned long get_nr_to_scan(struct lruvec *lruvec, struct scan_control *sc,
 221 -                                   bool can_swap, bool *need_aging)
 222 +                                   bool can_swap)
 223  {
 224         unsigned long nr_to_scan;
 225         struct mem_cgroup *memcg = lruvec_memcg(lruvec);
 226         DEFINE_MAX_SEQ(lruvec);
 227 -       DEFINE_MIN_SEQ(lruvec);
 228
 229         if (mem_cgroup_below_min(memcg) ||
 230             (mem_cgroup_below_low(memcg) && !sc->memcg_low_reclaim))
 231                 return 0;
 232
 233 -       *need_aging = should_run_aging(lruvec, max_seq, min_seq, sc, can_swap, &nr_to_scan);
 234 -       if (!*need_aging)
 235 +       if (!should_run_aging(lruvec, max_seq, sc, can_swap, &nr_to_scan))
 236                 return nr_to_scan;
 237
 238         /* skip the aging path at the default priority */
 239         if (sc->priority == DEF_PRIORITY)
 240 -               goto done;
 241 +               return nr_to_scan;
 242
 243 -       /* leave the work to lru_gen_age_node() */
 244 -       if (current_is_kswapd())
 245 -               return 0;
 246 +       try_to_inc_max_seq(lruvec, max_seq, sc, can_swap, false);
 247
 248 -       if (try_to_inc_max_seq(lruvec, max_seq, sc, can_swap, false))
 249 -               return nr_to_scan;
 250 -done:
 251 -       return min_seq[!can_swap] + MIN_NR_GENS <= max_seq ? nr_to_scan : 0;
 252 +       /* skip this lruvec as it's low on cold folios */
 253 +       return 0;
 254  }
 255
 256  static unsigned long get_nr_to_reclaim(struct scan_control *sc)
 257 @@ -5158,9 +5156,7 @@ static unsigned long get_nr_to_reclaim(s
 258  static void lru_gen_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
 259  {
 260         struct blk_plug plug;
 261 -       bool need_aging = false;
 262         unsigned long scanned = 0;
 263 -       unsigned long reclaimed = sc->nr_reclaimed;
 264         unsigned long nr_to_reclaim = get_nr_to_reclaim(sc);
 265
 266         lru_add_drain();
 267 @@ -5181,13 +5177,13 @@ static void lru_gen_shrink_lruvec(struct
 268                 else
 269                         swappiness = 0;
 270
 271 -               nr_to_scan = get_nr_to_scan(lruvec, sc, swappiness, &need_aging);
 272 +               nr_to_scan = get_nr_to_scan(lruvec, sc, swappiness);
 273                 if (!nr_to_scan)
 274 -                       goto done;
 275 +                       break;
 276
 277                 delta = evict_folios(lruvec, sc, swappiness);
 278                 if (!delta)
 279 -                       goto done;
 280 +                       break;
 281
 282                 scanned += delta;
 283                 if (scanned >= nr_to_scan)
 284 @@ -5199,10 +5195,6 @@ static void lru_gen_shrink_lruvec(struct
 285                 cond_resched();
 286         }
 287
 288 -       /* see the comment in lru_gen_age_node() */
 289 -       if (sc->nr_reclaimed - reclaimed >= MIN_LRU_BATCH && !need_aging)
 290 -               sc->memcgs_need_aging = false;
 291 -done:
 292         clear_mm_walk();
 293
 294         blk_finish_plug(&plug);