core: log cgroup legacy and unified hierarchy setting translations

To accommodate changes in kernel interface, cgroup unified hierarchy support
added several configuration items which overlap with the existing resource
control settings and there is simple config translation between the overlapping
settings to ease the transition.  As why certain cgroup knobs are being
configured can become confusing, this patch adds a master warning message which
is printed once when such translation is first used and logs each translation
with a debug message.

v2:

- Switched to log_unit*().

1 files changed, 63 insertions, 11 deletions

diff --git a/src/core/cgroup.c b/src/core/cgroup.c
index d1fb405e9a..f3e0c54b76 100644
--- a/src/core/cgroup.c
+++ b/src/core/cgroup.c
@@ -36,6 +36,22 @@
 
 #define CGROUP_CPU_QUOTA_PERIOD_USEC ((usec_t) 100 * USEC_PER_MSEC)
 
+static void cgroup_compat_warn(void)
+{
+        static bool cgroup_compat_warned = false;
+
+        if (cgroup_compat_warned)
+                return;
+
+        log_warning("cgroup compatibility translation between legacy and unified hierarchy settings activated. See cgroup-compat debug messages for details.");
+        cgroup_compat_warned = true;
+}
+
+#define log_cgroup_compat(unit, fmt, ...) do {                                  \
+                cgroup_compat_warn();                                           \
+                log_unit_debug(unit, "cgroup-compat: " fmt, ##__VA_ARGS__);     \
+        } while (0)
+
 void cgroup_context_init(CGroupContext *c) {
         assert(c);
 
@@ -587,9 +603,14 @@ static void cgroup_context_apply(Unit *u, CGroupMask mask, ManagerState state) {
 
                         if (has_io)
                                 weight = cgroup_context_io_weight(c, state);
-                        else if (has_blockio)
-                                weight = cgroup_weight_blkio_to_io(cgroup_context_blkio_weight(c, state));
-                        else
+                        else if (has_blockio) {
+                                uint64_t blkio_weight = cgroup_context_blkio_weight(c, state);
+
+                                weight = cgroup_weight_blkio_to_io(blkio_weight);
+
+                                log_cgroup_compat(u, "Applying [Startup]BlockIOWeight %" PRIu64 " as [Startup]IOWeight %" PRIu64,
+                                                  blkio_weight, weight);
+                        } else
                                 weight = CGROUP_WEIGHT_DEFAULT;
 
                         xsprintf(buf, "default %" PRIu64 "\n", weight);
@@ -608,8 +629,14 @@ static void cgroup_context_apply(Unit *u, CGroupMask mask, ManagerState state) {
                                 CGroupBlockIODeviceWeight *w;
 
                                 /* FIXME: no way to reset this list */
-                                LIST_FOREACH(device_weights, w, c->blockio_device_weights)
-                                        cgroup_apply_io_device_weight(u, w->path, cgroup_weight_blkio_to_io(w->weight));
+                                LIST_FOREACH(device_weights, w, c->blockio_device_weights) {
+                                        weight = cgroup_weight_blkio_to_io(w->weight);
+
+                                        log_cgroup_compat(u, "Applying BlockIODeviceWeight %" PRIu64 " as IODeviceWeight %" PRIu64 " for %s",
+                                                          w->weight, weight, w->path);
+
+                                        cgroup_apply_io_device_weight(u, w->path, weight);
+                                }
                         }
                 }
 
@@ -634,6 +661,9 @@ static void cgroup_context_apply(Unit *u, CGroupMask mask, ManagerState state) {
                                 limits[CGROUP_IO_RBPS_MAX] = b->rbps;
                                 limits[CGROUP_IO_WBPS_MAX] = b->wbps;
 
+                                log_cgroup_compat(u, "Applying BlockIO{Read|Write}Bandwidth %" PRIu64 " %" PRIu64 " as IO{Read|Write}BandwidthMax for %s",
+                                                  b->rbps, b->wbps, b->path);
+
                                 if (!cgroup_apply_io_device_limit(u, b->path, limits))
                                         cgroup_context_free_blockio_device_bandwidth(c, b);
                         }
@@ -650,9 +680,14 @@ static void cgroup_context_apply(Unit *u, CGroupMask mask, ManagerState state) {
 
                         if (has_blockio)
                                 weight = cgroup_context_blkio_weight(c, state);
-                        else if (has_io)
+                        else if (has_io) {
+                                uint64_t io_weight = cgroup_context_io_weight(c, state);
+
                                 weight = cgroup_weight_io_to_blkio(cgroup_context_io_weight(c, state));
-                        else
+
+                                log_cgroup_compat(u, "Applying [Startup]IOWeight %" PRIu64 " as [Startup]BlockIOWeight %" PRIu64,
+                                                  io_weight, weight);
+                        } else
                                 weight = CGROUP_BLKIO_WEIGHT_DEFAULT;
 
                         xsprintf(buf, "%" PRIu64 "\n", weight);
@@ -671,8 +706,14 @@ static void cgroup_context_apply(Unit *u, CGroupMask mask, ManagerState state) {
                                 CGroupIODeviceWeight *w;
 
                                 /* FIXME: no way to reset this list */
-                                LIST_FOREACH(device_weights, w, c->io_device_weights)
-                                        cgroup_apply_blkio_device_weight(u, w->path, cgroup_weight_io_to_blkio(w->weight));
+                                LIST_FOREACH(device_weights, w, c->io_device_weights) {
+                                        weight = cgroup_weight_io_to_blkio(w->weight);
+
+                                        log_cgroup_compat(u, "Applying IODeviceWeight %" PRIu64 " as BlockIODeviceWeight %" PRIu64 " for %s",
+                                                          w->weight, weight, w->path);
+
+                                        cgroup_apply_blkio_device_weight(u, w->path, weight);
+                                }
                         }
                 }
 
@@ -688,6 +729,9 @@ static void cgroup_context_apply(Unit *u, CGroupMask mask, ManagerState state) {
                         CGroupIODeviceLimit *l, *next;
 
                         LIST_FOREACH_SAFE(device_limits, l, next, c->io_device_limits) {
+                                log_cgroup_compat(u, "Applying IO{Read|Write}Bandwidth %" PRIu64 " %" PRIu64 " as BlockIO{Read|Write}BandwidthMax for %s",
+                                                  l->limits[CGROUP_IO_RBPS_MAX], l->limits[CGROUP_IO_WBPS_MAX], l->path);
+
                                 if (!cgroup_apply_blkio_device_limit(u, l->path, l->limits[CGROUP_IO_RBPS_MAX], l->limits[CGROUP_IO_WBPS_MAX]))
                                         cgroup_context_free_io_device_limit(c, l);
                         }
@@ -700,9 +744,13 @@ static void cgroup_context_apply(Unit *u, CGroupMask mask, ManagerState state) {
 
                         if (cgroup_context_has_unified_memory_config(c))
                                 max = c->memory_max;
-                        else
+                        else {
                                 max = c->memory_limit;
 
+                                if (max != CGROUP_LIMIT_MAX)
+                                        log_cgroup_compat(u, "Applying MemoryLimit %" PRIu64 " as MemoryMax", max);
+                        }
+
                         cgroup_apply_unified_memory_limit(u, "memory.low", c->memory_low);
                         cgroup_apply_unified_memory_limit(u, "memory.high", c->memory_high);
                         cgroup_apply_unified_memory_limit(u, "memory.max", max);
@@ -711,9 +759,13 @@ static void cgroup_context_apply(Unit *u, CGroupMask mask, ManagerState state) {
 
                         if (c->memory_limit != CGROUP_LIMIT_MAX)
                                 xsprintf(buf, "%" PRIu64 "\n", c->memory_limit);
-                        else
+                        else {
                                 xsprintf(buf, "%" PRIu64 "\n", c->memory_max);
 
+                                if (c->memory_max != CGROUP_LIMIT_MAX)
+                                        log_cgroup_compat(u, "Applying MemoryMax %" PRIu64 " as MemoryLimit", c->memory_max);
+                        }
+
                         r = cg_set_attribute("memory", path, "memory.limit_in_bytes", buf);
                         if (r < 0)
                                 log_unit_full(u, IN_SET(r, -ENOENT, -EROFS, -EACCES) ? LOG_DEBUG : LOG_WARNING, r,