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mm/mglru: try to stop at high watermarks 

The initial MGLRU patchset didn't include the memcg LRU support, and it
relied on should_abort_scan(), added by commit f76c833788 ("mm:
multi-gen LRU: optimize multiple memcgs"), to "backoff to avoid
overshooting their aggregate reclaim target by too much".

Later on when the memcg LRU was added, should_abort_scan() was deemed
unnecessary, and the test results [1] showed no side effects after it was
removed by commit a579086c99 ("mm: multi-gen LRU: remove eviction
fairness safeguard").

However, that test used memory.reclaim, which sets nr_to_reclaim to
SWAP_CLUSTER_MAX.  So it can overshoot only by SWAP_CLUSTER_MAX-1 pages,
i.e., from nr_reclaimed=nr_to_reclaim-1 to
nr_reclaimed=nr_to_reclaim+SWAP_CLUSTER_MAX-1.  Compared with the batch
size kswapd sets to nr_to_reclaim, SWAP_CLUSTER_MAX is tiny.  Therefore
that test isn't able to reproduce the worst case scenario, i.e., kswapd
overshooting GBs on large systems and "consuming 100% CPU" (see the Closes
tag).

Bring back a simplified version of should_abort_scan() on top of the memcg
LRU, so that kswapd stops when all eligible zones are above their
respective high watermarks plus a small delta to lower the chance of
KSWAPD_HIGH_WMARK_HIT_QUICKLY.  Note that this only applies to order-0
reclaim, meaning compaction-induced reclaim can still run wild (which is a
different problem).

On Android, launching 55 apps sequentially:
           Before     After      Change
  pgpgin   838377172  802955040  -4%
  pgpgout  38037080   34336300   -10%

[1] https://lore.kernel.org/20221222041905.2431096-1-yuzhao@google.com/

Link: https://lkml.kernel.org/r/20231208061407.2125867-2-yuzhao@google.com
Fixes: a579086c99 ("mm: multi-gen LRU: remove eviction fairness safeguard")
Signed-off-by: Yu Zhao <yuzhao@google.com>
Reported-by: Charan Teja Kalla <quic_charante@quicinc.com>
Reported-by: Jaroslav Pulchart <jaroslav.pulchart@gooddata.com>
Closes: https://lore.kernel.org/CAK8fFZ4DY+GtBA40Pm7Nn5xCHy+51w3sfxPqkqpqakSXYyX+Wg@mail.gmail.com/
Tested-by: Jaroslav Pulchart <jaroslav.pulchart@gooddata.com>
Tested-by: Kalesh Singh <kaleshsingh@google.com>
Cc: Hillf Danton <hdanton@sina.com>
Cc: Kairui Song <ryncsn@gmail.com>
Cc: T.J. Mercier <tjmercier@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Yu Zhao 2023-12-07 23:14:05 -07:00 committed by Andrew Morton
parent 081488051d
commit 5095a2b239
1 changed files with 28 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

36
mm/vmscan.c
View File

@ -4648,20 +4648,41 @@ static long get_nr_to_scan(struct lruvec *lruvec, struct scan_control *sc, bool
return try_to_inc_max_seq(lruvec, max_seq, sc, can_swap, false) ? -1 : 0;
}
static unsigned long get_nr_to_reclaim(struct scan_control *sc)
static bool should_abort_scan(struct lruvec *lruvec, struct scan_control *sc)
{
int i;
enum zone_watermarks mark;
/* don't abort memcg reclaim to ensure fairness */
if (!root_reclaim(sc))
return -1;
return false;
return max(sc->nr_to_reclaim, compact_gap(sc->order));
if (sc->nr_reclaimed >= max(sc->nr_to_reclaim, compact_gap(sc->order)))
return true;
/* check the order to exclude compaction-induced reclaim */
if (!current_is_kswapd() || sc->order)
return false;
mark = sysctl_numa_balancing_mode & NUMA_BALANCING_MEMORY_TIERING ?
WMARK_PROMO : WMARK_HIGH;
for (i = 0; i <= sc->reclaim_idx; i++) {
struct zone *zone = lruvec_pgdat(lruvec)->node_zones + i;
unsigned long size = wmark_pages(zone, mark) + MIN_LRU_BATCH;
if (managed_zone(zone) && !zone_watermark_ok(zone, 0, size, sc->reclaim_idx, 0))
return false;
}
/* kswapd should abort if all eligible zones are safe */
return true;
}
static bool try_to_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
{
long nr_to_scan;
unsigned long scanned = 0;
unsigned long nr_to_reclaim = get_nr_to_reclaim(sc);
int swappiness = get_swappiness(lruvec, sc);
/* clean file folios are more likely to exist */
@ -4683,7 +4704,7 @@ static bool try_to_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
if (scanned >= nr_to_scan)
break;
if (sc->nr_reclaimed >= nr_to_reclaim)
if (should_abort_scan(lruvec, sc))
break;
cond_resched();
@ -4744,7 +4765,6 @@ static void shrink_many(struct pglist_data *pgdat, struct scan_control *sc)
struct lru_gen_folio *lrugen;
struct mem_cgroup *memcg;
const struct hlist_nulls_node *pos;
unsigned long nr_to_reclaim = get_nr_to_reclaim(sc);
bin = first_bin = get_random_u32_below(MEMCG_NR_BINS);
restart:
@ -4777,7 +4797,7 @@ restart:
rcu_read_lock();
if (sc->nr_reclaimed >= nr_to_reclaim)
if (should_abort_scan(lruvec, sc))
break;
}
@ -4788,7 +4808,7 @@ restart:
mem_cgroup_put(memcg);
if (sc->nr_reclaimed >= nr_to_reclaim)
if (!is_a_nulls(pos))
return;
/* restart if raced with lru_gen_rotate_memcg() */