This is a note to let you know that I've just added the patch titled
mm/mglru: try to stop at high watermarks
to the 6.6-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
mm-mglru-try-to-stop-at-high-watermarks.patch
and it can be found in the queue-6.6 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 5095a2b23987d3c3c47dd16b3d4080e2733b8bb9 Mon Sep 17 00:00:00 2001
From: Yu Zhao <yuzhao@xxxxxxxxxx>
Date: Thu, 7 Dec 2023 23:14:05 -0700
Subject: mm/mglru: try to stop at high watermarks
From: Yu Zhao <yuzhao@xxxxxxxxxx>
commit 5095a2b23987d3c3c47dd16b3d4080e2733b8bb9 upstream.
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@xxxxxxxxxx/
Link: https://lkml.kernel.org/r/20231208061407.2125867-2-yuzhao@xxxxxxxxxx
Fixes: a579086c99ed ("mm: multi-gen LRU: remove eviction fairness safeguard")
Signed-off-by: Yu Zhao <yuzhao@xxxxxxxxxx>
Reported-by: Charan Teja Kalla <quic_charante@xxxxxxxxxxx>
Reported-by: Jaroslav Pulchart <jaroslav.pulchart@xxxxxxxxxxxx>
Closes: https://lore.kernel.org/CAK8fFZ4DY+GtBA40Pm7Nn5xCHy+51w3sfxPqkqpqakSXYyX+Wg@xxxxxxxxxxxxxx/
Tested-by: Jaroslav Pulchart <jaroslav.pulchart@xxxxxxxxxxxx>
Tested-by: Kalesh Singh <kaleshsingh@xxxxxxxxxx>
Cc: Hillf Danton <hdanton@xxxxxxxx>
Cc: Kairui Song <ryncsn@xxxxxxxxx>
Cc: T.J. Mercier <tjmercier@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
mm/vmscan.c | 36 ++++++++++++++++++++++++++++--------
1 file changed, 28 insertions(+), 8 deletions(-)
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -5341,20 +5341,41 @@ static long get_nr_to_scan(struct lruvec
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;
+
+ 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;
+ }
- return max(sc->nr_to_reclaim, compact_gap(sc->order));
+ /* 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 */
@@ -5376,7 +5397,7 @@ static bool try_to_shrink_lruvec(struct
if (scanned >= nr_to_scan)
break;
- if (sc->nr_reclaimed >= nr_to_reclaim)
+ if (should_abort_scan(lruvec, sc))
break;
cond_resched();
@@ -5437,7 +5458,6 @@ static void shrink_many(struct pglist_da
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:
@@ -5470,7 +5490,7 @@ restart:
rcu_read_lock();
- if (sc->nr_reclaimed >= nr_to_reclaim)
+ if (should_abort_scan(lruvec, sc))
break;
}
@@ -5481,7 +5501,7 @@ 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() */
Patches currently in stable-queue which might be from yuzhao@xxxxxxxxxx are
queue-6.6/mm-mglru-fix-underprotected-page-cache.patch
queue-6.6/mm-mglru-respect-min_ttl_ms-with-memcgs.patch
queue-6.6/mm-mglru-try-to-stop-at-high-watermarks.patch
queue-6.6/mm-mglru-reclaim-offlined-memcgs-harder.patch
