The patch titled
Subject: mm: multi-gen LRU: remove MM_LEAF_OLD and MM_NONLEAF_TOTAL stats
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
mm-multi-gen-lru-remove-mm_leaf_old-and-mm_nonleaf_total-stats.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-multi-gen-lru-remove-mm_leaf_old-and-mm_nonleaf_total-stats.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Yu Zhao <yuzhao@xxxxxxxxxx>
Subject: mm: multi-gen LRU: remove MM_LEAF_OLD and MM_NONLEAF_TOTAL stats
Date: Sat, 19 Oct 2024 01:29:38 +0000
Patch series "mm: multi-gen LRU: Have secondary MMUs participate in
MM_WALK".
Today, the MM_WALK capability causes MGLRU to clear the young bit from
PMDs and PTEs during the page table walk before eviction, but MGLRU does
not call the clear_young() MMU notifier in this case. By not calling this
notifier, the MM walk takes less time/CPU, but it causes pages that are
accessed mostly through KVM / secondary MMUs to appear younger than they
should be.
We do call the clear_young() notifier today, but only when attempting to
evict the page, so we end up clearing young/accessed information less
frequently for secondary MMUs than for mm PTEs, and therefore they appear
younger and are less likely to be evicted. Therefore, memory that is
*not* being accessed mostly by KVM will be evicted *more* frequently,
worsening performance.
ChromeOS observed a tab-open latency regression when enabling MGLRU with a
setup that involved running a VM:
Tab-open latency histogram (ms)
Version p50 mean p95 p99 max
base 1315 1198 2347 3454 10319
mglru 2559 1311 7399 12060 43758
fix 1119 926 2470 4211 6947
This series replaces the final non-selftest patchs from this series[1],
which introduced a similar change (and a new MMU notifier) with KVM
optimizations. I'll send a separate series (to Sean and Paolo) for the
KVM optimizations.
This series also makes proactive reclaim with MGLRU possible for KVM
memory. I have verified that this functions correctly with the selftest
from [1], but given that that test is a KVM selftest, I'll send it with
the rest of the KVM optimizations later. Andrew, let me know if you'd
like to take the test now anyway.
[1]: https://lore.kernel.org/linux-mm/20240926013506.860253-18-jthoughton@xxxxxxxxxx/
This patch (of 2):
The removed stats, MM_LEAF_OLD and MM_NONLEAF_TOTAL, are not very helpful
and become more complicated to properly compute when adding
test/clear_young() notifiers in MGLRU's mm walk.
Link: https://lkml.kernel.org/r/20241019012940.3656292-1-jthoughton@xxxxxxxxxx
Link: https://lkml.kernel.org/r/20241019012940.3656292-2-jthoughton@xxxxxxxxxx
Fixes: bd74fdaea146 ("mm: multi-gen LRU: support page table walks")
Signed-off-by: Yu Zhao <yuzhao@xxxxxxxxxx>
Signed-off-by: James Houghton <jthoughton@xxxxxxxxxx>
Cc: Axel Rasmussen <axelrasmussen@xxxxxxxxxx>
Cc: David Matlack <dmatlack@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: David Stevens <stevensd@xxxxxxxxxx>
Cc: Oliver Upton <oliver.upton@xxxxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Sean Christopherson <seanjc@xxxxxxxxxx>
Cc: Wei Xu <weixugc@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/mmzone.h | 2 --
mm/vmscan.c | 14 +++++---------
2 files changed, 5 insertions(+), 11 deletions(-)
--- a/include/linux/mmzone.h~mm-multi-gen-lru-remove-mm_leaf_old-and-mm_nonleaf_total-stats
+++ a/include/linux/mmzone.h
@@ -458,9 +458,7 @@ struct lru_gen_folio {
enum {
MM_LEAF_TOTAL, /* total leaf entries */
- MM_LEAF_OLD, /* old leaf entries */
MM_LEAF_YOUNG, /* young leaf entries */
- MM_NONLEAF_TOTAL, /* total non-leaf entries */
MM_NONLEAF_FOUND, /* non-leaf entries found in Bloom filters */
MM_NONLEAF_ADDED, /* non-leaf entries added to Bloom filters */
NR_MM_STATS
--- a/mm/vmscan.c~mm-multi-gen-lru-remove-mm_leaf_old-and-mm_nonleaf_total-stats
+++ a/mm/vmscan.c
@@ -3399,7 +3399,6 @@ restart:
continue;
if (!pte_young(ptent)) {
- walk->mm_stats[MM_LEAF_OLD]++;
continue;
}
@@ -3552,7 +3551,6 @@ restart:
walk->mm_stats[MM_LEAF_TOTAL]++;
if (!pmd_young(val)) {
- walk->mm_stats[MM_LEAF_OLD]++;
continue;
}
@@ -3564,8 +3562,6 @@ restart:
continue;
}
- walk->mm_stats[MM_NONLEAF_TOTAL]++;
-
if (!walk->force_scan && should_clear_pmd_young()) {
if (!pmd_young(val))
continue;
@@ -5254,11 +5250,11 @@ static void lru_gen_seq_show_full(struct
for (tier = 0; tier < MAX_NR_TIERS; tier++) {
seq_printf(m, " %10d", tier);
for (type = 0; type < ANON_AND_FILE; type++) {
- const char *s = " ";
+ const char *s = "xxx";
unsigned long n[3] = {};
if (seq == max_seq) {
- s = "RT ";
+ s = "RTx";
n[0] = READ_ONCE(lrugen->avg_refaulted[type][tier]);
n[1] = READ_ONCE(lrugen->avg_total[type][tier]);
} else if (seq == min_seq[type] || NR_HIST_GENS > 1) {
@@ -5280,14 +5276,14 @@ static void lru_gen_seq_show_full(struct
seq_puts(m, " ");
for (i = 0; i < NR_MM_STATS; i++) {
- const char *s = " ";
+ const char *s = "xxxx";
unsigned long n = 0;
if (seq == max_seq && NR_HIST_GENS == 1) {
- s = "LOYNFA";
+ s = "TYFA";
n = READ_ONCE(mm_state->stats[hist][i]);
} else if (seq != max_seq && NR_HIST_GENS > 1) {
- s = "loynfa";
+ s = "tyfa";
n = READ_ONCE(mm_state->stats[hist][i]);
}
_
Patches currently in -mm which might be from yuzhao@xxxxxxxxxx are
mm-multi-gen-lru-remove-mm_leaf_old-and-mm_nonleaf_total-stats.patch
mm-multi-gen-lru-use-pteppmdp_clear_young_notify.patch
mm-page_alloc-keep-track-of-free-highatomic.patch
