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Subject[RFC PATCH 2/2] memcg: add memory.min
Date
The new memory.min limit is similar to memory.low, just no bypassing it
when reclaim is desparate. Prefer oom kills before reclaim memory below
memory.min. Sharing more code with memory_cgroup_low() is possible, but
the idea is posted here for simplicity.

Signed-off-by: Greg Thelen <gthelen@google.com>
---
include/linux/memcontrol.h | 8 ++++++
mm/memcontrol.c | 58 ++++++++++++++++++++++++++++++++++++++
mm/vmscan.c | 3 ++
3 files changed, 69 insertions(+)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index c46016bb25eb..22bb4a88653a 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -178,6 +178,7 @@ struct mem_cgroup {
struct page_counter tcpmem;

/* Normal memory consumption range */
+ unsigned long min;
unsigned long low;
unsigned long high;

@@ -281,6 +282,7 @@ static inline bool mem_cgroup_disabled(void)
return !cgroup_subsys_enabled(memory_cgrp_subsys);
}

+bool mem_cgroup_min(struct mem_cgroup *root, struct mem_cgroup *memcg);
bool mem_cgroup_low(struct mem_cgroup *root, struct mem_cgroup *memcg);

int mem_cgroup_try_charge(struct page *page, struct mm_struct *mm,
@@ -726,6 +728,12 @@ static inline void mem_cgroup_event(struct mem_cgroup *memcg,
{
}

+static inline bool mem_cgroup_min(struct mem_cgroup *root,
+ struct mem_cgroup *memcg)
+{
+ return false;
+}
+
static inline bool mem_cgroup_low(struct mem_cgroup *root,
struct mem_cgroup *memcg)
{
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 9668f620203a..b2aaed4003b4 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5058,6 +5058,36 @@ static u64 memory_current_read(struct cgroup_subsys_state *css,
return (u64)page_counter_read(&memcg->memory) * PAGE_SIZE;
}

+static int memory_min_show(struct seq_file *m, void *v)
+{
+ struct mem_cgroup *memcg = mem_cgroup_from_css(seq_css(m));
+ unsigned long min = READ_ONCE(memcg->min);
+
+ if (min == PAGE_COUNTER_MAX)
+ seq_puts(m, "max\n");
+ else
+ seq_printf(m, "%llu\n", (u64)min * PAGE_SIZE);
+
+ return 0;
+}
+
+static ssize_t memory_min_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));
+ unsigned long min;
+ int err;
+
+ buf = strstrip(buf);
+ err = page_counter_memparse(buf, "max", &min);
+ if (err)
+ return err;
+
+ memcg->min = min;
+
+ return nbytes;
+}
+
static int memory_low_show(struct seq_file *m, void *v)
{
struct mem_cgroup *memcg = mem_cgroup_from_css(seq_css(m));
@@ -5288,6 +5318,12 @@ static struct cftype memory_files[] = {
.flags = CFTYPE_NOT_ON_ROOT,
.read_u64 = memory_current_read,
},
+ {
+ .name = "min",
+ .flags = CFTYPE_NOT_ON_ROOT,
+ .seq_show = memory_min_show,
+ .write = memory_min_write,
+ },
{
.name = "low",
.flags = CFTYPE_NOT_ON_ROOT,
@@ -5336,6 +5372,28 @@ struct cgroup_subsys memory_cgrp_subsys = {
.early_init = 0,
};

+/**
+ * mem_cgroup_min returns true for a memcg below its min limit. Such memcg are
+ * excempt from reclaim.
+ */
+bool mem_cgroup_min(struct mem_cgroup *root, struct mem_cgroup *memcg)
+{
+ if (mem_cgroup_disabled())
+ return false;
+
+ if (!root)
+ root = root_mem_cgroup;
+
+ if (memcg == root)
+ return false;
+
+ for (; memcg != root; memcg = parent_mem_cgroup(memcg)) {
+ if (page_counter_read(&memcg->memory) <= memcg->min)
+ return true; /* protect */
+ }
+ return false; /* !protect */
+}
+
/**
* mem_cgroup_low - check if memory consumption is below the normal range
* @root: the top ancestor of the sub-tree being checked
diff --git a/mm/vmscan.c b/mm/vmscan.c
index cd5dc3faaa57..15ae19a38ad5 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2539,6 +2539,9 @@ static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc)
unsigned long reclaimed;
unsigned long scanned;

+ if (mem_cgroup_min(root, memcg))
+ continue;
+
if (mem_cgroup_low(root, memcg)) {
if (!sc->memcg_low_reclaim) {
sc->memcg_low_skipped = 1;
--
2.17.0.484.g0c8726318c-goog
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