core: add cgroup memory controller support on the unified hierarchy (#3315)

On the unified hierarchy, memory controller implements three control knobs -
low, high and max which enables more useable and versatile control over memory
usage.  This patch implements support for the three control knobs.

* MemoryLow, MemoryHigh and MemoryMax are added for memory.low, memory.high and
  memory.max, respectively.

* As all absolute limits on the unified hierarchy use "max" for no limit, make
  memory limit parse functions accept "max" in addition to "infinity" and
  document "max" for the new knobs.

* Implement compatibility translation between MemoryMax and MemoryLimit.

v2:

- Fixed missing else's in config_parse_memory_limit().
- Fixed missing newline when writing out drop-ins.
- Coding style updates to use "val > 0" instead of "val".
- Minor updates to documentation.

1 files changed, 47 insertions, 16 deletions

diff --git a/src/core/cgroup.c b/src/core/cgroup.c
index 0fb63b1bd1..fbe69df4e9 100644
--- a/src/core/cgroup.c
+++ b/src/core/cgroup.c
@@ -46,7 +46,10 @@ void cgroup_context_init(CGroupContext *c) {
         c->startup_cpu_shares = CGROUP_CPU_SHARES_INVALID;
         c->cpu_quota_per_sec_usec = USEC_INFINITY;
 
-        c->memory_limit = (uint64_t) -1;
+        c->memory_high = CGROUP_LIMIT_MAX;
+        c->memory_max = CGROUP_LIMIT_MAX;
+
+        c->memory_limit = CGROUP_LIMIT_MAX;
 
         c->io_weight = CGROUP_WEIGHT_INVALID;
         c->startup_io_weight = CGROUP_WEIGHT_INVALID;
@@ -147,6 +150,9 @@ void cgroup_context_dump(CGroupContext *c, FILE* f, const char *prefix) {
                 "%sStartupIOWeight=%" PRIu64 "\n"
                 "%sBlockIOWeight=%" PRIu64 "\n"
                 "%sStartupBlockIOWeight=%" PRIu64 "\n"
+                "%sMemoryLow=%" PRIu64 "\n"
+                "%sMemoryHigh=%" PRIu64 "\n"
+                "%sMemoryMax=%" PRIu64 "\n"
                 "%sMemoryLimit=%" PRIu64 "\n"
                 "%sTasksMax=%" PRIu64 "\n"
                 "%sDevicePolicy=%s\n"
@@ -163,6 +169,9 @@ void cgroup_context_dump(CGroupContext *c, FILE* f, const char *prefix) {
                 prefix, c->startup_io_weight,
                 prefix, c->blockio_weight,
                 prefix, c->startup_blockio_weight,
+                prefix, c->memory_low,
+                prefix, c->memory_high,
+                prefix, c->memory_max,
                 prefix, c->memory_limit,
                 prefix, c->tasks_max,
                 prefix, cgroup_device_policy_to_string(c->device_policy),
@@ -496,6 +505,23 @@ static unsigned cgroup_apply_blkio_device_limit(const char *path, const char *de
         return n;
 }
 
+static bool cgroup_context_has_unified_memory_config(CGroupContext *c) {
+        return c->memory_low > 0 || c->memory_high != CGROUP_LIMIT_MAX || c->memory_max != CGROUP_LIMIT_MAX;
+}
+
+static void cgroup_apply_unified_memory_limit(const char *path, const char *file, uint64_t v) {
+        char buf[DECIMAL_STR_MAX(uint64_t) + 1] = "max";
+        int r;
+
+        if (v != CGROUP_LIMIT_MAX)
+                xsprintf(buf, "%" PRIu64 "\n", v);
+
+        r = cg_set_attribute("memory", path, file, buf);
+        if (r < 0)
+                log_full_errno(IN_SET(r, -ENOENT, -EROFS, -EACCES) ? LOG_DEBUG : LOG_WARNING, r,
+                               "Failed to set %s on %s: %m", file, path);
+}
+
 void cgroup_context_apply(CGroupContext *c, CGroupMask mask, const char *path, ManagerState state) {
         bool is_root;
         int r;
@@ -662,26 +688,30 @@ void cgroup_context_apply(CGroupContext *c, CGroupMask mask, const char *path, M
         }
 
         if ((mask & CGROUP_MASK_MEMORY) && !is_root) {
-                if (c->memory_limit != (uint64_t) -1) {
-                        char buf[DECIMAL_STR_MAX(uint64_t) + 1];
-
-                        sprintf(buf, "%" PRIu64 "\n", c->memory_limit);
+                if (cg_unified() > 0) {
+                        uint64_t max = c->memory_max;
 
-                        if (cg_unified() <= 0)
-                                r = cg_set_attribute("memory", path, "memory.limit_in_bytes", buf);
+                        if (cgroup_context_has_unified_memory_config(c))
+                                max = c->memory_max;
                         else
-                                r = cg_set_attribute("memory", path, "memory.max", buf);
+                                max = c->memory_limit;
 
+                        cgroup_apply_unified_memory_limit(path, "memory.low", c->memory_low);
+                        cgroup_apply_unified_memory_limit(path, "memory.high", c->memory_high);
+                        cgroup_apply_unified_memory_limit(path, "memory.max", max);
                 } else {
-                        if (cg_unified() <= 0)
-                                r = cg_set_attribute("memory", path, "memory.limit_in_bytes", "-1");
+                        char buf[DECIMAL_STR_MAX(uint64_t) + 1];
+
+                        if (c->memory_limit != CGROUP_LIMIT_MAX)
+                                xsprintf(buf, "%" PRIu64 "\n", c->memory_limit);
                         else
-                                r = cg_set_attribute("memory", path, "memory.max", "max");
-                }
+                                xsprintf(buf, "%" PRIu64 "\n", c->memory_max);
 
-                if (r < 0)
-                        log_full_errno(IN_SET(r, -ENOENT, -EROFS, -EACCES) ? LOG_DEBUG : LOG_WARNING, r,
-                                       "Failed to set memory.limit_in_bytes/memory.max on %s: %m", path);
+                        r = cg_set_attribute("memory", path, "memory.limit_in_bytes", buf);
+                        if (r < 0)
+                                log_full_errno(IN_SET(r, -ENOENT, -EROFS, -EACCES) ? LOG_DEBUG : LOG_WARNING, r,
+                                               "Failed to set memory.limit_in_bytes on %s: %m", path);
+                }
         }
 
         if ((mask & CGROUP_MASK_DEVICES) && !is_root) {
@@ -778,7 +808,8 @@ CGroupMask cgroup_context_get_mask(CGroupContext *c) {
                 mask |= CGROUP_MASK_IO | CGROUP_MASK_BLKIO;
 
         if (c->memory_accounting ||
-            c->memory_limit != (uint64_t) -1)
+            c->memory_limit != CGROUP_LIMIT_MAX ||
+            cgroup_context_has_unified_memory_config(c))
                 mask |= CGROUP_MASK_MEMORY;
 
         if (c->device_allow ||