The patch titled
Subject: mm/vmstat: protect per cpu variables with preempt disable on RT
has been added to the -mm tree. Its filename is
mm-vmstat-protect-per-cpu-variables-with-preempt-disable-on-rt.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/mm-vmstat-protect-per-cpu-variables-with-preempt-disable-on-rt.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/mm-vmstat-protect-per-cpu-variables-with-preempt-disable-on-rt.patch
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------------------------------------------------------
From: Ingo Molnar <mingo@xxxxxxx>
Subject: mm/vmstat: protect per cpu variables with preempt disable on RT
Disable preemption on -RT for the vmstat code. On vanilla the code runs
in IRQ-off regions while on -RT it may not when stats are updated under a
local_lock. "preempt_disable" ensures that the same resources are not
updated in parallel due to preemption.
This patch differs from the preempt-rt version where __count_vm_event and
__count_vm_events are also protected. The counters are explicitly
"allowed to be to be racy" so there is no need to protect them from
preemption. Only the accurate page stats that are updated by a
read-modify-write need protection.
Link: https://lkml.kernel.org/r/20210723100034.13353-3-mgorman@xxxxxxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/vmstat.c | 12 ++++++++++++
1 file changed, 12 insertions(+)
--- a/mm/vmstat.c~mm-vmstat-protect-per-cpu-variables-with-preempt-disable-on-rt
+++ a/mm/vmstat.c
@@ -319,6 +319,7 @@ void __mod_zone_page_state(struct zone *
long x;
long t;
+ preempt_disable_rt();
x = delta + __this_cpu_read(*p);
t = __this_cpu_read(pcp->stat_threshold);
@@ -328,6 +329,7 @@ void __mod_zone_page_state(struct zone *
x = 0;
}
__this_cpu_write(*p, x);
+ preempt_enable_rt();
}
EXPORT_SYMBOL(__mod_zone_page_state);
@@ -350,6 +352,7 @@ void __mod_node_page_state(struct pglist
delta >>= PAGE_SHIFT;
}
+ preempt_disable_rt();
x = delta + __this_cpu_read(*p);
t = __this_cpu_read(pcp->stat_threshold);
@@ -359,6 +362,7 @@ void __mod_node_page_state(struct pglist
x = 0;
}
__this_cpu_write(*p, x);
+ preempt_enable_rt();
}
EXPORT_SYMBOL(__mod_node_page_state);
@@ -391,6 +395,7 @@ void __inc_zone_state(struct zone *zone,
s8 __percpu *p = pcp->vm_stat_diff + item;
s8 v, t;
+ preempt_disable_rt();
v = __this_cpu_inc_return(*p);
t = __this_cpu_read(pcp->stat_threshold);
if (unlikely(v > t)) {
@@ -399,6 +404,7 @@ void __inc_zone_state(struct zone *zone,
zone_page_state_add(v + overstep, zone, item);
__this_cpu_write(*p, -overstep);
}
+ preempt_enable_rt();
}
void __inc_node_state(struct pglist_data *pgdat, enum node_stat_item item)
@@ -409,6 +415,7 @@ void __inc_node_state(struct pglist_data
VM_WARN_ON_ONCE(vmstat_item_in_bytes(item));
+ preempt_disable_rt();
v = __this_cpu_inc_return(*p);
t = __this_cpu_read(pcp->stat_threshold);
if (unlikely(v > t)) {
@@ -417,6 +424,7 @@ void __inc_node_state(struct pglist_data
node_page_state_add(v + overstep, pgdat, item);
__this_cpu_write(*p, -overstep);
}
+ preempt_enable_rt();
}
void __inc_zone_page_state(struct page *page, enum zone_stat_item item)
@@ -437,6 +445,7 @@ void __dec_zone_state(struct zone *zone,
s8 __percpu *p = pcp->vm_stat_diff + item;
s8 v, t;
+ preempt_disable_rt();
v = __this_cpu_dec_return(*p);
t = __this_cpu_read(pcp->stat_threshold);
if (unlikely(v < - t)) {
@@ -445,6 +454,7 @@ void __dec_zone_state(struct zone *zone,
zone_page_state_add(v - overstep, zone, item);
__this_cpu_write(*p, overstep);
}
+ preempt_enable_rt();
}
void __dec_node_state(struct pglist_data *pgdat, enum node_stat_item item)
@@ -455,6 +465,7 @@ void __dec_node_state(struct pglist_data
VM_WARN_ON_ONCE(vmstat_item_in_bytes(item));
+ preempt_disable_rt();
v = __this_cpu_dec_return(*p);
t = __this_cpu_read(pcp->stat_threshold);
if (unlikely(v < - t)) {
@@ -463,6 +474,7 @@ void __dec_node_state(struct pglist_data
node_page_state_add(v - overstep, pgdat, item);
__this_cpu_write(*p, overstep);
}
+ preempt_enable_rt();
}
void __dec_zone_page_state(struct page *page, enum zone_stat_item item)
_
Patches currently in -mm which might be from mingo@xxxxxxx are
mm-vmstat-protect-per-cpu-variables-with-preempt-disable-on-rt.patch
