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Subject[PATCH] mm: vmscan: memcg: Add global shrink priority
Date
Currently, memcg has some config to limit memory usage and config
the shrink behavior.
In the memory-constrained environment, put different priority tasks
into different cgroups with different memory limits to protect the
performance of the high priority tasks. Because the global memory
shrink will affect the performance of all tasks. The memory limit
cgroup can make shrink happen inside the cgroup. Then it can decrease
the memory shrink of the high priority task to protect its performance.

But the memory footprint of the task is not static. It will change as
the working pressure changes. And the version changes will affect it too.
Then set the appropriate memory limit to decrease the global memory shrink
is a difficult job and lead to wasted memory or performance loss sometimes.

This commit adds global shrink priority to memcg to try to handle this
problem.
The default global shrink priority of each cgroup is DEF_PRIORITY.
Its behavior in global shrink is not changed.
And when global shrink priority of a cgroup is smaller than DEF_PRIORITY,
its memory will be shrink when memcg->global_shrink_priority greater than
or equal to sc->priority.

The following is an example to use global shrink priority in a VM that
has 2 CPUs, 1G memory and 4G swap:
# These are test shells that call usemem that get from
# https://git.kernel.org/pub/scm/linux/kernel/git/wfg/vm-scalability.git
cat 1.sh
sleep 9999
# -s 3600: Sleep 3600 seconds after test complete then usemem will
# not release the memory at once.
# -Z: read memory again after access the memory.
# The first time access memory need shrink memory to allocate page.
# Then the access speed of high priority will not increase a lot.
# The read again speed of high priority will increase.
# $((850 * 1024 * 1024 + 8)): Different sizes are used to distinguish
# the results of the two tests.
usemem -s 3600 -Z -a -n 1 $((850 * 1024 * 1024 + 8))
cat 2.sh
sleep 9999
usemem -s 3600 -Z -a -n 1 $((850 * 1024 * 1024))

# Setup swap
swapon /swapfile
# Setup 2 cgroups
mkdir /sys/fs/cgroup/memory/t1/
mkdir /sys/fs/cgroup/memory/t2/

# Run tests with same global shrink priority
cat /sys/fs/cgroup/memory/t1/memory.global_shrink_priority
12
cat /sys/fs/cgroup/memory/t2/memory.global_shrink_priority
12
echo $$ > /sys/fs/cgroup/memory/t1/cgroup.procs
sh 1.sh &
echo $$ > /sys/fs/cgroup/memory/t2/cgroup.procs
sh 2.sh &
echo $$ > /sys/fs/cgroup/memory/cgroup.procs
killall sleep
# This the test results
1002700800 bytes / 2360359 usecs = 414852 KB/s
1002700809 bytes / 2676181 usecs = 365894 KB/s
read again 891289600 bytes / 13515142 usecs = 64401 KB/s
read again 891289608 bytes / 13252268 usecs = 65679 KB/s
killall usemem

# Run tests with 12 and 8
cat /sys/fs/cgroup/memory/t1/memory.global_shrink_priority
12
echo 8 > /sys/fs/cgroup/memory/t2/memory.global_shrink_priority
echo $$ > /sys/fs/cgroup/memory/t1/cgroup.procs
sh 1.sh &
echo $$ > /sys/fs/cgroup/memory/t2/cgroup.procs
sh 2.sh &
echo $$ > /sys/fs/cgroup/memory/cgroup.procs
killall sleep
# This the test results
1002700800 bytes / 1809056 usecs = 541276 KB/s
1002700809 bytes / 2184337 usecs = 448282 KB/s
read again 891289600 bytes / 6666224 usecs = 130568 KB/s
read again 891289608 bytes / 9171440 usecs = 94903 KB/s
killall usemem

# This is the test results of 12 and 6
1002700800 bytes / 1827914 usecs = 535692 KB/s
1002700809 bytes / 2135124 usecs = 458615 KB/s
read again 891289600 bytes / 1498419 usecs = 580878 KB/s
read again 891289608 bytes / 7328362 usecs = 118771 KB/s

Signed-off-by: Hui Zhu <teawaterz@linux.alibaba.com>
---
include/linux/memcontrol.h | 2 ++
mm/memcontrol.c | 32 ++++++++++++++++++++++++++++++++
mm/vmscan.c | 39 ++++++++++++++++++++++++++++++++++++---
3 files changed, 70 insertions(+), 3 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index a7a0a1a5..8ad2437 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -244,6 +244,8 @@ struct mem_cgroup {
/* OOM-Killer disable */
int oom_kill_disable;

+ s8 global_shrink_priority;
+
/* memory.events and memory.events.local */
struct cgroup_file events_file;
struct cgroup_file events_local_file;
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index c5b5f74..39fdc84 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4646,6 +4646,32 @@ static ssize_t memcg_write_event_control(struct kernfs_open_file *of,
return ret;
}

+static ssize_t mem_global_shrink_priority_write(struct kernfs_open_file *of,
+ char *buf, size_t nbytes, loff_t off)
+{
+ struct mem_cgroup *memcg = mem_cgroup_from_css(of_css(of));
+ s8 val;
+ int ret;
+
+ ret = kstrtos8(buf, 0, &val);
+ if (ret < 0)
+ return ret;
+ if (val > DEF_PRIORITY)
+ return -EINVAL;
+
+ memcg->global_shrink_priority = val;
+
+ return nbytes;
+}
+
+static s64 mem_global_shrink_priority_read(struct cgroup_subsys_state *css,
+ struct cftype *cft)
+{
+ struct mem_cgroup *memcg = mem_cgroup_from_css(css);
+
+ return memcg->global_shrink_priority;
+}
+
static struct cftype mem_cgroup_legacy_files[] = {
{
.name = "usage_in_bytes",
@@ -4774,6 +4800,11 @@ static struct cftype mem_cgroup_legacy_files[] = {
.write = mem_cgroup_reset,
.read_u64 = mem_cgroup_read_u64,
},
+ {
+ .name = "global_shrink_priority",
+ .write = mem_global_shrink_priority_write,
+ .read_s64 = mem_global_shrink_priority_read,
+ },
{ }, /* terminate */
};

@@ -4996,6 +5027,7 @@ mem_cgroup_css_alloc(struct cgroup_subsys_state *parent_css)

memcg->high = PAGE_COUNTER_MAX;
memcg->soft_limit = PAGE_COUNTER_MAX;
+ memcg->global_shrink_priority = DEF_PRIORITY;
if (parent) {
memcg->swappiness = mem_cgroup_swappiness(parent);
memcg->oom_kill_disable = parent->oom_kill_disable;
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 74e8edc..5e11d45 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2637,17 +2637,33 @@ static inline bool should_continue_reclaim(struct pglist_data *pgdat,
return inactive_lru_pages > pages_for_compaction;
}

+static bool get_is_global_shrink(struct scan_control *sc)
+{
+ if (!sc->target_mem_cgroup ||
+ mem_cgroup_is_root(sc->target_mem_cgroup))
+ return true;
+
+ return false;
+}
+
static void shrink_node_memcgs(pg_data_t *pgdat, struct scan_control *sc)
{
struct mem_cgroup *target_memcg = sc->target_mem_cgroup;
struct mem_cgroup *memcg;
+ bool is_global_shrink = get_is_global_shrink(sc);

memcg = mem_cgroup_iter(target_memcg, NULL, NULL);
do {
- struct lruvec *lruvec = mem_cgroup_lruvec(memcg, pgdat);
+ struct lruvec *lruvec;
unsigned long reclaimed;
unsigned long scanned;

+ if (is_global_shrink &&
+ memcg->global_shrink_priority < sc->priority)
+ continue;
+
+ lruvec = mem_cgroup_lruvec(memcg, pgdat);
+
switch (mem_cgroup_protected(target_memcg, memcg)) {
case MEMCG_PROT_MIN:
/*
@@ -2682,11 +2698,21 @@ static void shrink_node_memcgs(pg_data_t *pgdat, struct scan_control *sc)
reclaimed = sc->nr_reclaimed;
scanned = sc->nr_scanned;

+ if (is_global_shrink &&
+ memcg->global_shrink_priority != DEF_PRIORITY)
+ sc->priority += DEF_PRIORITY
+ - memcg->global_shrink_priority;
+
shrink_lruvec(lruvec, sc);

shrink_slab(sc->gfp_mask, pgdat->node_id, memcg,
sc->priority);

+ if (is_global_shrink &&
+ memcg->global_shrink_priority != DEF_PRIORITY)
+ sc->priority -= DEF_PRIORITY
+ - memcg->global_shrink_priority;
+
/* Record the group's reclaim efficiency */
vmpressure(sc->gfp_mask, memcg, false,
sc->nr_scanned - scanned,
@@ -3395,11 +3421,18 @@ static void age_active_anon(struct pglist_data *pgdat,

memcg = mem_cgroup_iter(NULL, NULL, NULL);
do {
+ if (memcg->global_shrink_priority < sc->priority)
+ continue;
+
lruvec = mem_cgroup_lruvec(memcg, pgdat);
+ /*
+ * Not set sc->priority according even if this is
+ * a global shrink because nr_to_scan is set to
+ * SWAP_CLUSTER_MAX and there is not other part use it.
+ */
shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
sc, LRU_ACTIVE_ANON);
- memcg = mem_cgroup_iter(NULL, memcg, NULL);
- } while (memcg);
+ } while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)));
}

static bool pgdat_watermark_boosted(pg_data_t *pgdat, int classzone_idx)
--
2.7.4
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