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...
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@google.com 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@google....
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@google.com Link: https://lkml.kernel.org/r/20241019012940.3656292-2-jthoughton@google.com Fixes: bd74fdaea146 ("mm: multi-gen LRU: support page table walks") Signed-off-by: Yu Zhao yuzhao@google.com Signed-off-by: James Houghton jthoughton@google.com Cc: Axel Rasmussen axelrasmussen@google.com Cc: David Matlack dmatlack@google.com Cc: David Rientjes rientjes@google.com Cc: David Stevens stevensd@google.com Cc: Oliver Upton oliver.upton@linux.dev Cc: Paolo Bonzini pbonzini@redhat.com Cc: Sean Christopherson seanjc@google.com Cc: Wei Xu weixugc@google.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---
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@google.com 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