The patch titled
Subject: mm/vmstat: remove remote node draining
has been added to the -mm mm-unstable branch. Its filename is
mm-vmstat-remove-remote-node-draining.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-vmstat-remove-remote-node-draining.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
Subject: mm/vmstat: remove remote node draining
Date: Fri, 03 Mar 2023 16:58:42 -0300
Patch series "fold per-CPU vmstats remotely", v3.
This patch series addresses the following two problems:
1. A customer provided some evidence which indicates that
the idle tick was stopped; albeit, CPU-specific vmstat
counters still remained populated.
Thus one can only assume quiet_vmstat() was not
invoked on return to the idle loop. If I understand
correctly, I suspect this divergence might erroneously
prevent a reclaim attempt by kswapd. If the number of
zone specific free pages are below their per-cpu drift
value then zone_page_state_snapshot() is used to
compute a more accurate view of the aforementioned
statistic. Thus any task blocked on the NUMA node
specific pfmemalloc_wait queue will be unable to make
significant progress via direct reclaim unless it is
killed after being woken up by kswapd
(see throttle_direct_reclaim())
2. With a SCHED_FIFO task that busy loops on a given CPU,
and kworker for that CPU at SCHED_OTHER priority,
queuing work to sync per-vmstats will either cause that
work to never execute, or stalld (i.e. stall daemon)
boosts kworker priority which causes a latency
violation
By having vmstat_shepherd flush the per-CPU counters to the global
counters from remote CPUs.
This is done using cmpxchg to manipulate the counters, both CPU locally
(via the account functions), and remotely (via cpu_vm_stats_fold).
Thanks to Aaron Tomlin for diagnosing issue 1 and writing the initial
patch series.
This patch (of 3):
Draining of pages from the local pcp for a remote zone should not be
necessary, since once the system is low on memory (or compaction on a
zone is in effect), drain_all_pages should be called freeing any unused
pcps.
For reference, the original commit which introduces remote node
draining is 4037d452202e34214e8a939fa5621b2b3bbb45b7.
Link: https://lkml.kernel.org/r/20230303195841.310844446@xxxxxxxxxx
Link: https://lkml.kernel.org/r/20230303195908.774798959@xxxxxxxxxx
Signed-off-by: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
Cc: Aaron Tomlin <atomlin@xxxxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Frederic Weisbecker <frederic@xxxxxxxxxx>
Cc: Heiko Carstens <hca@xxxxxxxxxxxxx>
Cc: Huacai Chen <chenhuacai@xxxxxxxxxx>
Cc: "Russell King (Oracle)" <linux@xxxxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
--- a/include/linux/mmzone.h~mm-vmstat-remove-remote-node-draining
+++ a/include/linux/mmzone.h
@@ -679,9 +679,6 @@ struct per_cpu_pages {
int high; /* high watermark, emptying needed */
int batch; /* chunk size for buddy add/remove */
short free_factor; /* batch scaling factor during free */
-#ifdef CONFIG_NUMA
- short expire; /* When 0, remote pagesets are drained */
-#endif
/* Lists of pages, one per migrate type stored on the pcp-lists */
struct list_head lists[NR_PCP_LISTS];
--- a/mm/page_alloc.c~mm-vmstat-remove-remote-node-draining
+++ a/mm/page_alloc.c
@@ -3107,26 +3107,6 @@ static int rmqueue_bulk(struct zone *zon
return i;
}
-#ifdef CONFIG_NUMA
-/*
- * Called from the vmstat counter updater to drain pagesets of this
- * currently executing processor on remote nodes after they have
- * expired.
- */
-void drain_zone_pages(struct zone *zone, struct per_cpu_pages *pcp)
-{
- int to_drain, batch;
-
- batch = READ_ONCE(pcp->batch);
- to_drain = min(pcp->count, batch);
- if (to_drain > 0) {
- spin_lock(&pcp->lock);
- free_pcppages_bulk(zone, to_drain, pcp, 0);
- spin_unlock(&pcp->lock);
- }
-}
-#endif
-
/*
* Drain pcplists of the indicated processor and zone.
*/
--- a/mm/vmstat.c~mm-vmstat-remove-remote-node-draining
+++ a/mm/vmstat.c
@@ -803,20 +803,16 @@ static int fold_diff(int *zone_diff, int
*
* The function returns the number of global counters updated.
*/
-static int refresh_cpu_vm_stats(bool do_pagesets)
+static int refresh_cpu_vm_stats(void)
{
struct pglist_data *pgdat;
struct zone *zone;
int i;
int global_zone_diff[NR_VM_ZONE_STAT_ITEMS] = { 0, };
int global_node_diff[NR_VM_NODE_STAT_ITEMS] = { 0, };
- int changes = 0;
for_each_populated_zone(zone) {
struct per_cpu_zonestat __percpu *pzstats = zone->per_cpu_zonestats;
-#ifdef CONFIG_NUMA
- struct per_cpu_pages __percpu *pcp = zone->per_cpu_pageset;
-#endif
for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++) {
int v;
@@ -826,44 +822,8 @@ static int refresh_cpu_vm_stats(bool do_
atomic_long_add(v, &zone->vm_stat[i]);
global_zone_diff[i] += v;
-#ifdef CONFIG_NUMA
- /* 3 seconds idle till flush */
- __this_cpu_write(pcp->expire, 3);
-#endif
}
}
-#ifdef CONFIG_NUMA
-
- if (do_pagesets) {
- cond_resched();
- /*
- * Deal with draining the remote pageset of this
- * processor
- *
- * Check if there are pages remaining in this pageset
- * if not then there is nothing to expire.
- */
- if (!__this_cpu_read(pcp->expire) ||
- !__this_cpu_read(pcp->count))
- continue;
-
- /*
- * We never drain zones local to this processor.
- */
- if (zone_to_nid(zone) == numa_node_id()) {
- __this_cpu_write(pcp->expire, 0);
- continue;
- }
-
- if (__this_cpu_dec_return(pcp->expire))
- continue;
-
- if (__this_cpu_read(pcp->count)) {
- drain_zone_pages(zone, this_cpu_ptr(pcp));
- changes++;
- }
- }
-#endif
}
for_each_online_pgdat(pgdat) {
@@ -880,8 +840,7 @@ static int refresh_cpu_vm_stats(bool do_
}
}
- changes += fold_diff(global_zone_diff, global_node_diff);
- return changes;
+ return fold_diff(global_zone_diff, global_node_diff);
}
/*
@@ -1873,7 +1832,7 @@ int sysctl_stat_interval __read_mostly =
#ifdef CONFIG_PROC_FS
static void refresh_vm_stats(struct work_struct *work)
{
- refresh_cpu_vm_stats(true);
+ refresh_cpu_vm_stats();
}
int vmstat_refresh(struct ctl_table *table, int write,
@@ -1883,6 +1842,8 @@ int vmstat_refresh(struct ctl_table *tab
int err;
int i;
+ drain_all_pages(NULL);
+
/*
* The regular update, every sysctl_stat_interval, may come later
* than expected: leaving a significant amount in per_cpu buckets.
@@ -1937,7 +1898,7 @@ int vmstat_refresh(struct ctl_table *tab
static void vmstat_update(struct work_struct *w)
{
- if (refresh_cpu_vm_stats(true)) {
+ if (refresh_cpu_vm_stats()) {
/*
* Counters were updated so we expect more updates
* to occur in the future. Keep on running the
@@ -2000,7 +1961,7 @@ void quiet_vmstat(void)
* it would be too expensive from this path.
* vmstat_shepherd will take care about that for us.
*/
- refresh_cpu_vm_stats(false);
+ refresh_cpu_vm_stats();
}
/*
_
Patches currently in -mm which might be from mtosatti@xxxxxxxxxx are
mm-vmstat-remove-remote-node-draining.patch
this_cpu_cmpxchg-arm64-switch-this_cpu_cmpxchg-to-locked-add-_local-function.patch
this_cpu_cmpxchg-loongarch-switch-this_cpu_cmpxchg-to-locked-add-_local-function.patch
this_cpu_cmpxchg-s390-switch-this_cpu_cmpxchg-to-locked-add-_local-function.patch
this_cpu_cmpxchg-x86-switch-this_cpu_cmpxchg-to-locked-add-_local-function.patch
add-this_cpu_cmpxchg_local-and-asm-generic-definitions.patch
convert-this_cpu_cmpxchg-users-to-this_cpu_cmpxchg_local.patch
mm-vmstat-switch-counter-modification-to-cmpxchg.patch
mm-vmstat-use-xchg-in-cpu_vm_stats_fold.patch
mm-vmstat-switch-vmstat-shepherd-to-flush-per-cpu-counters-remotely.patch
mm-vmstat-refresh-stats-remotely-instead-of-via-work-item.patch
