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authorYu Zhao <yuzhao@google.com>2023-12-07 23:14:05 -0700
committerAndrew Morton <akpm@linux-foundation.org>2023-12-12 17:20:19 -0800
commit5095a2b23987d3c3c47dd16b3d4080e2733b8bb9 (patch)
tree3853738a25220cbb70fa825c131d911c688c02ba /mm/vmscan.c
parent081488051d28d32569ebb7c7a23572778b2e7d57 (diff)
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 f76c83378851 ("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 a579086c99ed ("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: a579086c99ed ("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>
Diffstat (limited to 'mm/vmscan.c')
-rw-r--r--mm/vmscan.c36
1 files changed, 28 insertions, 8 deletions
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 540333f5415c..bb7dacd8f753 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -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;
+
+ 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;
- return max(sc->nr_to_reclaim, compact_gap(sc->order));
+ 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() */