From: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Subject: mm/page_alloc: introduce vm.percpu_pagelist_high_fraction
This introduces a new sysctl vm.percpu_pagelist_high_fraction. It is
similar to the old vm.percpu_pagelist_fraction. The old sysctl increased
both pcp->batch and pcp->high with the higher pcp->high potentially
reducing zone->lock contention. However, the higher pcp->batch value also
potentially increased allocation latency while the PCP was refilled. This
sysctl only adjusts pcp->high so that zone->lock contention is potentially
reduced but allocation latency during a PCP refill remains the same.
# grep -E "high:|batch" /proc/zoneinfo | tail -2
high: 649
batch: 63
# sysctl vm.percpu_pagelist_high_fraction=8
# grep -E "high:|batch" /proc/zoneinfo | tail -2
high: 35071
batch: 63
# sysctl vm.percpu_pagelist_high_fraction=64
high: 4383
batch: 63
# sysctl vm.percpu_pagelist_high_fraction=0
high: 649
batch: 63
[mgorman@xxxxxxxxxxxxxxxxxxx: fix documentation]
Link: https://lkml.kernel.org/r/20210528151010.GQ30378@xxxxxxxxxxxxxxxxxxx
Link: https://lkml.kernel.org/r/20210525080119.5455-7-mgorman@xxxxxxxxxxxxxxxxxxx
Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Acked-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Hillf Danton <hdanton@xxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
Documentation/admin-guide/sysctl/vm.rst | 21 ++++++
include/linux/mmzone.h | 3
kernel/sysctl.c | 8 ++
mm/page_alloc.c | 69 +++++++++++++++++++---
4 files changed, 94 insertions(+), 7 deletions(-)
--- a/Documentation/admin-guide/sysctl/vm.rst~mm-page_alloc-introduce-vmpercpu_pagelist_high_fraction
+++ a/Documentation/admin-guide/sysctl/vm.rst
@@ -64,6 +64,7 @@ Currently, these files are in /proc/sys/
- overcommit_ratio
- page-cluster
- panic_on_oom
+- percpu_pagelist_high_fraction
- stat_interval
- stat_refresh
- numa_stat
@@ -789,6 +790,26 @@ panic_on_oom=2+kdump gives you very stro
why oom happens. You can get snapshot.
+percpu_pagelist_high_fraction
+=============================
+
+This is the fraction of pages in each zone that are can be stored to
+per-cpu page lists. It is an upper boundary that is divided depending
+on the number of online CPUs. The min value for this is 8 which means
+that we do not allow more than 1/8th of pages in each zone to be stored
+on per-cpu page lists. This entry only changes the value of hot per-cpu
+page lists. A user can specify a number like 100 to allocate 1/100th of
+each zone between per-cpu lists.
+
+The batch value of each per-cpu page list remains the same regardless of
+the value of the high fraction so allocation latencies are unaffected.
+
+The initial value is zero. Kernel uses this value to set the high pcp->high
+mark based on the low watermark for the zone and the number of local
+online CPUs. If the user writes '0' to this sysctl, it will revert to
+this default behavior.
+
+
stat_interval
=============
--- a/include/linux/mmzone.h~mm-page_alloc-introduce-vmpercpu_pagelist_high_fraction
+++ a/include/linux/mmzone.h
@@ -1029,12 +1029,15 @@ int watermark_scale_factor_sysctl_handle
extern int sysctl_lowmem_reserve_ratio[MAX_NR_ZONES];
int lowmem_reserve_ratio_sysctl_handler(struct ctl_table *, int, void *,
size_t *, loff_t *);
+int percpu_pagelist_high_fraction_sysctl_handler(struct ctl_table *, int,
+ void *, size_t *, loff_t *);
int sysctl_min_unmapped_ratio_sysctl_handler(struct ctl_table *, int,
void *, size_t *, loff_t *);
int sysctl_min_slab_ratio_sysctl_handler(struct ctl_table *, int,
void *, size_t *, loff_t *);
int numa_zonelist_order_handler(struct ctl_table *, int,
void *, size_t *, loff_t *);
+extern int percpu_pagelist_high_fraction;
extern char numa_zonelist_order[];
#define NUMA_ZONELIST_ORDER_LEN 16
--- a/kernel/sysctl.c~mm-page_alloc-introduce-vmpercpu_pagelist_high_fraction
+++ a/kernel/sysctl.c
@@ -2909,6 +2909,14 @@ static struct ctl_table vm_table[] = {
.extra2 = &one_thousand,
},
{
+ .procname = "percpu_pagelist_high_fraction",
+ .data = &percpu_pagelist_high_fraction,
+ .maxlen = sizeof(percpu_pagelist_high_fraction),
+ .mode = 0644,
+ .proc_handler = percpu_pagelist_high_fraction_sysctl_handler,
+ .extra1 = SYSCTL_ZERO,
+ },
+ {
.procname = "page_lock_unfairness",
.data = &sysctl_page_lock_unfairness,
.maxlen = sizeof(sysctl_page_lock_unfairness),
--- a/mm/page_alloc.c~mm-page_alloc-introduce-vmpercpu_pagelist_high_fraction
+++ a/mm/page_alloc.c
@@ -120,6 +120,7 @@ typedef int __bitwise fpi_t;
/* prevent >1 _updater_ of zone percpu pageset ->high and ->batch fields */
static DEFINE_MUTEX(pcp_batch_high_lock);
+#define MIN_PERCPU_PAGELIST_HIGH_FRACTION (8)
struct pagesets {
local_lock_t lock;
@@ -192,6 +193,7 @@ EXPORT_SYMBOL(_totalram_pages);
unsigned long totalreserve_pages __read_mostly;
unsigned long totalcma_pages __read_mostly;
+int percpu_pagelist_high_fraction;
gfp_t gfp_allowed_mask __read_mostly = GFP_BOOT_MASK;
DEFINE_STATIC_KEY_MAYBE(CONFIG_INIT_ON_ALLOC_DEFAULT_ON, init_on_alloc);
EXPORT_SYMBOL(init_on_alloc);
@@ -6725,17 +6727,32 @@ static int zone_highsize(struct zone *zo
#ifdef CONFIG_MMU
int high;
int nr_local_cpus;
+ unsigned long total_pages;
+
+ if (!percpu_pagelist_high_fraction) {
+ /*
+ * By default, the high value of the pcp is based on the zone
+ * low watermark so that if they are full then background
+ * reclaim will not be started prematurely.
+ */
+ total_pages = low_wmark_pages(zone);
+ } else {
+ /*
+ * If percpu_pagelist_high_fraction is configured, the high
+ * value is based on a fraction of the managed pages in the
+ * zone.
+ */
+ total_pages = zone_managed_pages(zone) / percpu_pagelist_high_fraction;
+ }
/*
- * The high value of the pcp is based on the zone low watermark
- * so that if they are full then background reclaim will not be
- * started prematurely. The value is split across all online CPUs
- * local to the zone. Note that early in boot that CPUs may not be
- * online yet and that during CPU hotplug that the cpumask is not
- * yet updated when a CPU is being onlined.
+ * Split the high value across all online CPUs local to the zone. Note
+ * that early in boot that CPUs may not be online yet and that during
+ * CPU hotplug that the cpumask is not yet updated when a CPU is being
+ * onlined.
*/
nr_local_cpus = max(1U, cpumask_weight(cpumask_of_node(zone_to_nid(zone)))) + cpu_online;
- high = low_wmark_pages(zone) / nr_local_cpus;
+ high = total_pages / nr_local_cpus;
/*
* Ensure high is at least batch*4. The multiple is based on the
@@ -8500,6 +8517,44 @@ int lowmem_reserve_ratio_sysctl_handler(
return 0;
}
+/*
+ * percpu_pagelist_high_fraction - changes the pcp->high for each zone on each
+ * cpu. It is the fraction of total pages in each zone that a hot per cpu
+ * pagelist can have before it gets flushed back to buddy allocator.
+ */
+int percpu_pagelist_high_fraction_sysctl_handler(struct ctl_table *table,
+ int write, void *buffer, size_t *length, loff_t *ppos)
+{
+ struct zone *zone;
+ int old_percpu_pagelist_high_fraction;
+ int ret;
+
+ mutex_lock(&pcp_batch_high_lock);
+ old_percpu_pagelist_high_fraction = percpu_pagelist_high_fraction;
+
+ ret = proc_dointvec_minmax(table, write, buffer, length, ppos);
+ if (!write || ret < 0)
+ goto out;
+
+ /* Sanity checking to avoid pcp imbalance */
+ if (percpu_pagelist_high_fraction &&
+ percpu_pagelist_high_fraction < MIN_PERCPU_PAGELIST_HIGH_FRACTION) {
+ percpu_pagelist_high_fraction = old_percpu_pagelist_high_fraction;
+ ret = -EINVAL;
+ goto out;
+ }
+
+ /* No change? */
+ if (percpu_pagelist_high_fraction == old_percpu_pagelist_high_fraction)
+ goto out;
+
+ for_each_populated_zone(zone)
+ zone_set_pageset_high_and_batch(zone, 0);
+out:
+ mutex_unlock(&pcp_batch_high_lock);
+ return ret;
+}
+
#ifndef __HAVE_ARCH_RESERVED_KERNEL_PAGES
/*
* Returns the number of pages that arch has reserved but
_
