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mm: multi-gen LRU: rename lru_gen_struct to lru_gen_folio 

Patch series "mm: multi-gen LRU: memcg LRU", v3.

Overview
========

An memcg LRU is a per-node LRU of memcgs.  It is also an LRU of LRUs,
since each node and memcg combination has an LRU of folios (see
mem_cgroup_lruvec()).

Its goal is to improve the scalability of global reclaim, which is
critical to system-wide memory overcommit in data centers.  Note that
memcg reclaim is currently out of scope.

Its memory bloat is a pointer to each lruvec and negligible to each
pglist_data.  In terms of traversing memcgs during global reclaim, it
improves the best-case complexity from O(n) to O(1) and does not affect
the worst-case complexity O(n).  Therefore, on average, it has a sublinear
complexity in contrast to the current linear complexity.

The basic structure of an memcg LRU can be understood by an analogy to
the active/inactive LRU (of folios):
1. It has the young and the old (generations), i.e., the counterparts
   to the active and the inactive;
2. The increment of max_seq triggers promotion, i.e., the counterpart
   to activation;
3. Other events trigger similar operations, e.g., offlining an memcg
   triggers demotion, i.e., the counterpart to deactivation.

In terms of global reclaim, it has two distinct features:
1. Sharding, which allows each thread to start at a random memcg (in
   the old generation) and improves parallelism;
2. Eventual fairness, which allows direct reclaim to bail out at will
   and reduces latency without affecting fairness over some time.

The commit message in patch 6 details the workflow:
https://lore.kernel.org/r/20221222041905.2431096-7-yuzhao@google.com/

The following is a simple test to quickly verify its effectiveness.

  Test design:
  1. Create multiple memcgs.
  2. Each memcg contains a job (fio).
  3. All jobs access the same amount of memory randomly.
  4. The system does not experience global memory pressure.
  5. Periodically write to the root memory.reclaim.

  Desired outcome:
  1. All memcgs have similar pgsteal counts, i.e., stddev(pgsteal)
     over mean(pgsteal) is close to 0%.
  2. The total pgsteal is close to the total requested through
     memory.reclaim, i.e., sum(pgsteal) over sum(requested) is close
     to 100%.

  Actual outcome [1]:
                                     MGLRU off    MGLRU on
  stddev(pgsteal) / mean(pgsteal)    75%          20%
  sum(pgsteal) / sum(requested)      425%         95%

  ####################################################################
  MEMCGS=128

  for ((memcg = 0; memcg < $MEMCGS; memcg++)); do
      mkdir /sys/fs/cgroup/memcg$memcg
  done

  start() {
      echo $BASHPID > /sys/fs/cgroup/memcg$memcg/cgroup.procs

      fio -name=memcg$memcg --numjobs=1 --ioengine=mmap \
          --filename=/dev/zero --size=1920M --rw=randrw \
          --rate=64m,64m --random_distribution=random \
          --fadvise_hint=0 --time_based --runtime=10h \
          --group_reporting --minimal
  }

  for ((memcg = 0; memcg < $MEMCGS; memcg++)); do
      start &
  done

  sleep 600

  for ((i = 0; i < 600; i++)); do
      echo 256m >/sys/fs/cgroup/memory.reclaim
      sleep 6
  done

  for ((memcg = 0; memcg < $MEMCGS; memcg++)); do
      grep "pgsteal " /sys/fs/cgroup/memcg$memcg/memory.stat
  done
  ####################################################################

[1]: This was obtained from running the above script (touches less
     than 256GB memory) on an EPYC 7B13 with 512GB DRAM for over an
     hour.


This patch (of 8):

The new name lru_gen_folio will be more distinct from the coming
lru_gen_memcg.

Link: https://lkml.kernel.org/r/20221222041905.2431096-1-yuzhao@google.com
Link: https://lkml.kernel.org/r/20221222041905.2431096-2-yuzhao@google.com
Signed-off-by: Yu Zhao <yuzhao@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Michael Larabel <Michael@MichaelLarabel.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Yu Zhao 2022-12-21 21:18:59 -07:00 committed by Andrew Morton
parent 14687619e1
commit 391655fe08
4 changed files with 24 additions and 24 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
include/linux/mm_inline.h
View File

@ -178,7 +178,7 @@ static inline void lru_gen_update_size(struct lruvec *lruvec, struct folio *foli
int zone = folio_zonenum(folio);
int delta = folio_nr_pages(folio);
enum lru_list lru = type * LRU_INACTIVE_FILE;
struct lru_gen_struct *lrugen = &lruvec->lrugen;
struct lru_gen_folio *lrugen = &lruvec->lrugen;
VM_WARN_ON_ONCE(old_gen != -1 && old_gen >= MAX_NR_GENS);
VM_WARN_ON_ONCE(new_gen != -1 && new_gen >= MAX_NR_GENS);
@ -224,7 +224,7 @@ 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);
struct lru_gen_struct *lrugen = &lruvec->lrugen;
struct lru_gen_folio *lrugen = &lruvec->lrugen;
VM_WARN_ON_ONCE_FOLIO(gen != -1, folio);

6
include/linux/mmzone.h
View File

@ -404,7 +404,7 @@ enum {
* The number of pages in each generation is eventually consistent and therefore
* can be transiently negative when reset_batch_size() is pending.
*/
struct lru_gen_struct {
struct lru_gen_folio {
/* the aging increments the youngest generation number */
unsigned long max_seq;
/* the eviction increments the oldest generation numbers */
@ -461,7 +461,7 @@ struct lru_gen_mm_state {
struct lru_gen_mm_walk {
/* the lruvec under reclaim */
struct lruvec *lruvec;
/* unstable max_seq from lru_gen_struct */
/* unstable max_seq from lru_gen_folio */
unsigned long max_seq;
/* the next address within an mm to scan */
unsigned long next_addr;
@ -524,7 +524,7 @@ struct lruvec {
unsigned long flags;
#ifdef CONFIG_LRU_GEN
/* evictable pages divided into generations */
struct lru_gen_struct lrugen;
struct lru_gen_folio lrugen;
/* to concurrently iterate lru_gen_mm_list */
struct lru_gen_mm_state mm_state;
#endif

34
mm/vmscan.c
View File

@ -3215,7 +3215,7 @@ static int get_nr_gens(struct lruvec *lruvec, int type)
static bool __maybe_unused seq_is_valid(struct lruvec *lruvec)
{
/* see the comment on lru_gen_struct */
/* see the comment on lru_gen_folio */
return get_nr_gens(lruvec, LRU_GEN_FILE) >= MIN_NR_GENS &&
get_nr_gens(lruvec, LRU_GEN_FILE) <= get_nr_gens(lruvec, LRU_GEN_ANON) &&
get_nr_gens(lruvec, LRU_GEN_ANON) <= MAX_NR_GENS;
@ -3612,7 +3612,7 @@ struct ctrl_pos {
static void read_ctrl_pos(struct lruvec *lruvec, int type, int tier, int gain,
struct ctrl_pos *pos)
{
struct lru_gen_struct *lrugen = &lruvec->lrugen;
struct lru_gen_folio *lrugen = &lruvec->lrugen;
int hist = lru_hist_from_seq(lrugen->min_seq[type]);
pos->refaulted = lrugen->avg_refaulted[type][tier] +
@ -3627,7 +3627,7 @@ static void read_ctrl_pos(struct lruvec *lruvec, int type, int tier, int gain,
static void reset_ctrl_pos(struct lruvec *lruvec, int type, bool carryover)
{
int hist, tier;
struct lru_gen_struct *lrugen = &lruvec->lrugen;
struct lru_gen_folio *lrugen = &lruvec->lrugen;
bool clear = carryover ? NR_HIST_GENS == 1 : NR_HIST_GENS > 1;
unsigned long seq = carryover ? lrugen->min_seq[type] : lrugen->max_seq + 1;
@ -3704,7 +3704,7 @@ static int folio_update_gen(struct folio *folio, int gen)
static int folio_inc_gen(struct lruvec *lruvec, struct folio *folio, bool reclaiming)
{
int type = folio_is_file_lru(folio);
struct lru_gen_struct *lrugen = &lruvec->lrugen;
struct lru_gen_folio *lrugen = &lruvec->lrugen;
int new_gen, old_gen = lru_gen_from_seq(lrugen->min_seq[type]);
unsigned long new_flags, old_flags = READ_ONCE(folio->flags);
@ -3749,7 +3749,7 @@ static void update_batch_size(struct lru_gen_mm_walk *walk, struct folio *folio,
static void reset_batch_size(struct lruvec *lruvec, struct lru_gen_mm_walk *walk)
{
int gen, type, zone;
struct lru_gen_struct *lrugen = &lruvec->lrugen;
struct lru_gen_folio *lrugen = &lruvec->lrugen;
walk->batched = 0;
@ -4263,7 +4263,7 @@ static bool inc_min_seq(struct lruvec *lruvec, int type, bool can_swap)
{
int zone;
int remaining = MAX_LRU_BATCH;
struct lru_gen_struct *lrugen = &lruvec->lrugen;
struct lru_gen_folio *lrugen = &lruvec->lrugen;
int new_gen, old_gen = lru_gen_from_seq(lrugen->min_seq[type]);
if (type == LRU_GEN_ANON && !can_swap)
@ -4299,7 +4299,7 @@ static bool try_to_inc_min_seq(struct lruvec *lruvec, bool can_swap)
{
int gen, type, zone;
bool success = false;
struct lru_gen_struct *lrugen = &lruvec->lrugen;
struct lru_gen_folio *lrugen = &lruvec->lrugen;
DEFINE_MIN_SEQ(lruvec);
VM_WARN_ON_ONCE(!seq_is_valid(lruvec));
@ -4320,7 +4320,7 @@ next:
;
}
/* see the comment on lru_gen_struct */
/* see the comment on lru_gen_folio */
if (can_swap) {
min_seq[LRU_GEN_ANON] = min(min_seq[LRU_GEN_ANON], min_seq[LRU_GEN_FILE]);
min_seq[LRU_GEN_FILE] = max(min_seq[LRU_GEN_ANON], lrugen->min_seq[LRU_GEN_FILE]);
@ -4342,7 +4342,7 @@ static void inc_max_seq(struct lruvec *lruvec, bool can_swap, bool force_scan)
{
int prev, next;
int type, zone;
struct lru_gen_struct *lrugen = &lruvec->lrugen;
struct lru_gen_folio *lrugen = &lruvec->lrugen;
spin_lock_irq(&lruvec->lru_lock);
@ -4400,7 +4400,7 @@ static bool try_to_inc_max_seq(struct lruvec *lruvec, unsigned long max_seq,
bool success;
struct lru_gen_mm_walk *walk;
struct mm_struct *mm = NULL;
struct lru_gen_struct *lrugen = &lruvec->lrugen;
struct lru_gen_folio *lrugen = &lruvec->lrugen;
VM_WARN_ON_ONCE(max_seq > READ_ONCE(lrugen->max_seq));
@ -4465,7 +4465,7 @@ static bool should_run_aging(struct lruvec *lruvec, unsigned long max_seq, unsig
unsigned long old = 0;
unsigned long young = 0;
unsigned long total = 0;
struct lru_gen_struct *lrugen = &lruvec->lrugen;
struct lru_gen_folio *lrugen = &lruvec->lrugen;
struct mem_cgroup *memcg = lruvec_memcg(lruvec);
for (type = !can_swap; type < ANON_AND_FILE; type++) {
@ -4750,7 +4750,7 @@ static bool sort_folio(struct lruvec *lruvec, struct folio *folio, int tier_idx)
int delta = folio_nr_pages(folio);
int refs = folio_lru_refs(folio);
int tier = lru_tier_from_refs(refs);
struct lru_gen_struct *lrugen = &lruvec->lrugen;
struct lru_gen_folio *lrugen = &lruvec->lrugen;
VM_WARN_ON_ONCE_FOLIO(gen >= MAX_NR_GENS, folio);
@ -4850,7 +4850,7 @@ static int scan_folios(struct lruvec *lruvec, struct scan_control *sc,
int scanned = 0;
int isolated = 0;
int remaining = MAX_LRU_BATCH;
struct lru_gen_struct *lrugen = &lruvec->lrugen;
struct lru_gen_folio *lrugen = &lruvec->lrugen;
struct mem_cgroup *memcg = lruvec_memcg(lruvec);
VM_WARN_ON_ONCE(!list_empty(list));
@ -5251,7 +5251,7 @@ done:
static bool __maybe_unused state_is_valid(struct lruvec *lruvec)
{
struct lru_gen_struct *lrugen = &lruvec->lrugen;
struct lru_gen_folio *lrugen = &lruvec->lrugen;
if (lrugen->enabled) {
enum lru_list lru;
@ -5530,7 +5530,7 @@ static void lru_gen_seq_show_full(struct seq_file *m, struct lruvec *lruvec,
int i;
int type, tier;
int hist = lru_hist_from_seq(seq);
struct lru_gen_struct *lrugen = &lruvec->lrugen;
struct lru_gen_folio *lrugen = &lruvec->lrugen;
for (tier = 0; tier < MAX_NR_TIERS; tier++) {
seq_printf(m, " %10d", tier);
@ -5580,7 +5580,7 @@ static int lru_gen_seq_show(struct seq_file *m, void *v)
unsigned long seq;
bool full = !debugfs_real_fops(m->file)->write;
struct lruvec *lruvec = v;
struct lru_gen_struct *lrugen = &lruvec->lrugen;
struct lru_gen_folio *lrugen = &lruvec->lrugen;
int nid = lruvec_pgdat(lruvec)->node_id;
struct mem_cgroup *memcg = lruvec_memcg(lruvec);
DEFINE_MAX_SEQ(lruvec);
@ -5834,7 +5834,7 @@ void lru_gen_init_lruvec(struct lruvec *lruvec)
{
int i;
int gen, type, zone;
struct lru_gen_struct *lrugen = &lruvec->lrugen;
struct lru_gen_folio *lrugen = &lruvec->lrugen;
lrugen->max_seq = MIN_NR_GENS + 1;
lrugen->enabled = lru_gen_enabled();

4
mm/workingset.c
View File

@ -223,7 +223,7 @@ static void *lru_gen_eviction(struct folio *folio)
unsigned long token;
unsigned long min_seq;
struct lruvec *lruvec;
struct lru_gen_struct *lrugen;
struct lru_gen_folio *lrugen;
int type = folio_is_file_lru(folio);
int delta = folio_nr_pages(folio);
int refs = folio_lru_refs(folio);
@ -252,7 +252,7 @@ static void lru_gen_refault(struct folio *folio, void *shadow)
unsigned long token;
unsigned long min_seq;
struct lruvec *lruvec;
struct lru_gen_struct *lrugen;
struct lru_gen_folio *lrugen;
struct mem_cgroup *memcg;
struct pglist_data *pgdat;
int type = folio_is_file_lru(folio);