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Subject[patch 3/5] mm: vmstat: optionally flush per-CPU vmstat counters on return to userspace
The logic to disable vmstat worker thread, when entering
nohz full, does not cover all scenarios. For example, it is possible
for the following to happen:

1) enter nohz_full, which calls refresh_cpu_vm_stats, syncing the stats.
2) app runs mlock, which increases counters for mlock'ed pages.
3) start -RT loop

Since refresh_cpu_vm_stats from nohz_full logic can happen _before_
the mlock, vmstat shepherd can restart vmstat worker thread on
the CPU in question.

To fix this, optionally sync the vmstat counters when returning
from userspace, controllable by a new "vmstat_sync" isolcpus
flags (default off).

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

Index: linux-2.6-vmstat-update/kernel/sched/isolation.c
===================================================================
--- linux-2.6-vmstat-update.orig/kernel/sched/isolation.c
+++ linux-2.6-vmstat-update/kernel/sched/isolation.c
@@ -8,6 +8,7 @@
*
*/
#include "sched.h"
+#include <linux/vmstat.h>

DEFINE_STATIC_KEY_FALSE(housekeeping_overridden);
EXPORT_SYMBOL_GPL(housekeeping_overridden);
@@ -129,6 +130,9 @@ static int __init housekeeping_setup(cha
}
}

+ if (flags & HK_FLAG_VMSTAT_SYNC)
+ static_branch_enable(&vmstat_sync_enabled);
+
housekeeping_flags |= flags;

free_bootmem_cpumask_var(non_housekeeping_mask);
Index: linux-2.6-vmstat-update/include/linux/vmstat.h
===================================================================
--- linux-2.6-vmstat-update.orig/include/linux/vmstat.h
+++ linux-2.6-vmstat-update/include/linux/vmstat.h
@@ -21,6 +21,15 @@ int sysctl_vm_numa_stat_handler(struct c
void *buffer, size_t *length, loff_t *ppos);
#endif

+DECLARE_STATIC_KEY_FALSE(vmstat_sync_enabled);
+
+extern void __sync_vmstat(void);
+static inline void sync_vmstat(void)
+{
+ if (static_branch_unlikely(&vmstat_sync_enabled))
+ __sync_vmstat();
+}
+
struct reclaim_stat {
unsigned nr_dirty;
unsigned nr_unqueued_dirty;
Index: linux-2.6-vmstat-update/mm/vmstat.c
===================================================================
--- linux-2.6-vmstat-update.orig/mm/vmstat.c
+++ linux-2.6-vmstat-update/mm/vmstat.c
@@ -28,6 +28,7 @@
#include <linux/mm_inline.h>
#include <linux/page_ext.h>
#include <linux/page_owner.h>
+#include <linux/sched/isolation.h>

#include "internal.h"

@@ -308,6 +309,24 @@ void set_pgdat_percpu_threshold(pg_data_
}
}

+DEFINE_STATIC_KEY_FALSE(vmstat_sync_enabled);
+static DEFINE_PER_CPU_ALIGNED(bool, vmstat_dirty);
+
+static inline void mark_vmstat_dirty(void)
+{
+ int cpu;
+
+ if (!static_branch_unlikely(&vmstat_sync_enabled))
+ return;
+
+ cpu = smp_processor_id();
+
+ if (housekeeping_cpu(cpu, HK_FLAG_VMSTAT_SYNC))
+ return;
+
+ per_cpu(vmstat_dirty, smp_processor_id()) = true;
+}
+
/*
* For use when we know that interrupts are disabled,
* or when we know that preemption is disabled and that
@@ -330,6 +349,7 @@ void __mod_zone_page_state(struct zone *
x = 0;
}
__this_cpu_write(*p, x);
+ mark_vmstat_dirty();
}
EXPORT_SYMBOL(__mod_zone_page_state);

@@ -361,6 +381,7 @@ void __mod_node_page_state(struct pglist
x = 0;
}
__this_cpu_write(*p, x);
+ mark_vmstat_dirty();
}
EXPORT_SYMBOL(__mod_node_page_state);

@@ -401,6 +422,7 @@ void __inc_zone_state(struct zone *zone,
zone_page_state_add(v + overstep, zone, item);
__this_cpu_write(*p, -overstep);
}
+ mark_vmstat_dirty();
}

void __inc_node_state(struct pglist_data *pgdat, enum node_stat_item item)
@@ -419,6 +441,7 @@ void __inc_node_state(struct pglist_data
node_page_state_add(v + overstep, pgdat, item);
__this_cpu_write(*p, -overstep);
}
+ mark_vmstat_dirty();
}

void __inc_zone_page_state(struct page *page, enum zone_stat_item item)
@@ -447,6 +470,7 @@ void __dec_zone_state(struct zone *zone,
zone_page_state_add(v - overstep, zone, item);
__this_cpu_write(*p, overstep);
}
+ mark_vmstat_dirty();
}

void __dec_node_state(struct pglist_data *pgdat, enum node_stat_item item)
@@ -465,6 +489,7 @@ void __dec_node_state(struct pglist_data
node_page_state_add(v - overstep, pgdat, item);
__this_cpu_write(*p, overstep);
}
+ mark_vmstat_dirty();
}

void __dec_zone_page_state(struct page *page, enum zone_stat_item item)
@@ -528,6 +553,7 @@ static inline void mod_zone_state(struct

if (z)
zone_page_state_add(z, zone, item);
+ mark_vmstat_dirty();
}

void mod_zone_page_state(struct zone *zone, enum zone_stat_item item,
@@ -596,6 +622,7 @@ static inline void mod_node_state(struct

if (z)
node_page_state_add(z, pgdat, item);
+ mark_vmstat_dirty();
}

void mod_node_page_state(struct pglist_data *pgdat, enum node_stat_item item,
@@ -2006,6 +2033,32 @@ static void vmstat_shepherd(struct work_
round_jiffies_relative(sysctl_stat_interval));
}

+void __sync_vmstat(void)
+{
+ int cpu;
+
+ cpu = get_cpu();
+ if (per_cpu(vmstat_dirty, cpu) == false) {
+ put_cpu();
+ return;
+ }
+
+ refresh_cpu_vm_stats(false);
+ per_cpu(vmstat_dirty, cpu) = false;
+ put_cpu();
+
+ /*
+ * If task is migrated to another CPU between put_cpu
+ * and cancel_delayed_work_sync, the code below might
+ * cancel vmstat_update work for a different cpu
+ * (than the one from which the vmstats were flushed).
+ *
+ * However, vmstat shepherd will re-enable it later,
+ * so its harmless.
+ */
+ cancel_delayed_work_sync(&per_cpu(vmstat_work, cpu));
+}
+
static void __init start_shepherd_timer(void)
{
int cpu;
Index: linux-2.6-vmstat-update/kernel/entry/common.c
===================================================================
--- linux-2.6-vmstat-update.orig/kernel/entry/common.c
+++ linux-2.6-vmstat-update/kernel/entry/common.c
@@ -6,6 +6,7 @@
#include <linux/livepatch.h>
#include <linux/audit.h>
#include <linux/tick.h>
+#include <linux/vmstat.h>

#include "common.h"

@@ -290,6 +291,7 @@ static void syscall_exit_to_user_mode_pr
*/
static void isolation_exit_to_user_mode_prepare(void)
{
+ sync_vmstat();
}

static __always_inline void __syscall_exit_to_user_mode_work(struct pt_regs *regs)

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