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| 1 | +#!/usr/bin/env python3 |
| 2 | +"""cgroup2 support for DIRAC pilot.""" |
| 3 | + |
| 4 | +import os |
| 5 | +import functools |
| 6 | +import subprocess |
| 7 | +from DIRAC import S_OK, S_ERROR, gLogger |
| 8 | +from DIRAC.Core.Utilities.DIRACSingleton import DIRACSingleton |
| 9 | +from DIRAC.Core.Utilities import Subprocess |
| 10 | + |
| 11 | + |
| 12 | +class CG2Manager(metaclass=DIRACSingleton): |
| 13 | + """A class to manage cgroup2 hierachy for a typical pilot job use-case. |
| 14 | +
|
| 15 | + This creates a group for all of the pilot processes (anything in the |
| 16 | + group at the start. This is a requirement for controlling the |
| 17 | + sub-groups (no processes in non-leaf groups). |
| 18 | +
|
| 19 | + A group is then created on request for each "slot" under the pilot, |
| 20 | + with the requested limits. |
| 21 | + """ |
| 22 | + |
| 23 | + # Paths used to lookup cgroup info |
| 24 | + FILE_MOUNTS = "/proc/mounts" |
| 25 | + FILE_CUR_CGROUP = f"/proc/{os.getpid()}/cgroup" |
| 26 | + # Control file names within the cgroup2 hierachy |
| 27 | + CTRL_CONTROLLERS = "cgroup.controllers" |
| 28 | + CTRL_PROCS = "cgroup.procs" |
| 29 | + CTRL_SUBTREE = "cgroup.subtree_control" |
| 30 | + CTRL_MEM_OOM_GROUP = "memory.oom.group" |
| 31 | + CTRL_MEM_EVENTS = "memory.events" |
| 32 | + CTRL_MEM_MAX = "memory.max" |
| 33 | + CTRL_MEM_SWAP_MAX = "memory.swap.max" |
| 34 | + CTRL_MEM_PEAK = "memory.peak" |
| 35 | + CTRL_CPU_MAX = "cpu.max" |
| 36 | + # CPU controller constants |
| 37 | + # Weight is the max value for 1 CPU core |
| 38 | + CPU_WEIGHT = 100000 |
| 39 | + # Period is the averaging time in us to apply the limit |
| 40 | + # The default is 100k and I see no particularly reason this should change |
| 41 | + CPU_PERIOD = 100000 |
| 42 | + # Name of the group for the existing pilot processes |
| 43 | + PILOT_GROUP = f"dirac_pilot_{os.getpid()}" |
| 44 | + |
| 45 | + def __init__(self): |
| 46 | + """Set-up CGroup2 manager.""" |
| 47 | + # This boolean will be set to True if the cgroups are configured |
| 48 | + # in the expected way |
| 49 | + self._ready = False |
| 50 | + # A counter of number of subgroups created |
| 51 | + # Used to create unique group names |
| 52 | + self._subproc_num = 0 |
| 53 | + # Physical path to the starting cgroup for this process |
| 54 | + # (i.e. the base of our hierachy) |
| 55 | + self._cgroup_path = None |
| 56 | + # Logger |
| 57 | + self.log = gLogger.getSubLogger("CG2Manager") |
| 58 | + |
| 59 | + @staticmethod |
| 60 | + def _filter_file(path, filterfcn): |
| 61 | + """Opens a file and runs filterfcn for each line. |
| 62 | + If filterfcn returns any value, that value will be returned |
| 63 | + by this function. |
| 64 | + Returns None if no line matches. |
| 65 | + """ |
| 66 | + with open(path, encoding="ascii") as file_in: |
| 67 | + for line in file_in.readlines(): |
| 68 | + line = line.strip() |
| 69 | + if res := filterfcn(line): |
| 70 | + return res |
| 71 | + return None |
| 72 | + |
| 73 | + def _detect_root(self): |
| 74 | + """Find the cgroup2 filesystem mountpoint on this system. |
| 75 | + Returns the mountpoint path or None if it isn't found. |
| 76 | + """ |
| 77 | + |
| 78 | + def filt(line): |
| 79 | + """Filter function to find the first cgroup2 mount point |
| 80 | + from a standard /proc/mounts layout file. |
| 81 | + """ |
| 82 | + parts = line.split(" ") |
| 83 | + if len(parts) < 3: |
| 84 | + return None |
| 85 | + if parts[2] == "cgroup2": |
| 86 | + return parts[1] |
| 87 | + return None |
| 88 | + |
| 89 | + return self._filter_file(self.FILE_MOUNTS, filt) |
| 90 | + |
| 91 | + def _detect_path(self): |
| 92 | + """Finds the full physical path to the current cgroup control dir. |
| 93 | + Sets self._cgroup_path on success. |
| 94 | + Raises a RuntimeError if the path cannot be determined. |
| 95 | + """ |
| 96 | + |
| 97 | + def filt(line): |
| 98 | + """Filter to find the current cgroup2 name for the current |
| 99 | + process, without the leading /. |
| 100 | + """ |
| 101 | + if line.startswith("0::/"): |
| 102 | + return line[4:] |
| 103 | + return False |
| 104 | + |
| 105 | + if not (root_path := self._detect_root()): |
| 106 | + raise RuntimeError("Failed to find cgroup mount point") |
| 107 | + if not (cur_group := self._filter_file(self.FILE_CUR_CGROUP, filt)): |
| 108 | + raise RuntimeError("Failed to find current cgroup") |
| 109 | + self._cgroup_path = os.path.join(root_path, cur_group) |
| 110 | + |
| 111 | + def _create_group(self, group_name, isolate_oom=True): |
| 112 | + """Creates a new group. |
| 113 | + If "isolate_oom" is True, the new group will be decoupled |
| 114 | + from the parent's OOM group. |
| 115 | + Raises a RuntimeError if the group cannot be created. |
| 116 | + """ |
| 117 | + try: |
| 118 | + os.mkdir(os.path.join(self._cgroup_path, group_name)) |
| 119 | + except PermissionError as err: |
| 120 | + raise RuntimeError(f"Permission denied creating sub-cgroup '{group_name}'") from err |
| 121 | + if isolate_oom: |
| 122 | + self._write_control(group_name, self.CTRL_MEM_OOM_GROUP, "0") |
| 123 | + |
| 124 | + def _remove_group(self, group_name): |
| 125 | + """Removes a group.""" |
| 126 | + os.rmdir(os.path.join(self._cgroup_path, group_name)) |
| 127 | + |
| 128 | + def _move_init_procs(self): |
| 129 | + """Creates the pilot sub-group and moves all of the initial processes |
| 130 | + from the top group into the new sub-group. |
| 131 | + Will raise a RuntimeError if any cgroup configuration problem |
| 132 | + prevents this from completing succesfully. |
| 133 | + """ |
| 134 | + self._create_group(self.PILOT_GROUP, isolate_oom=False) |
| 135 | + cur_pids = self._read_control("", self.CTRL_PROCS) |
| 136 | + self._write_control(self.PILOT_GROUP, self.CTRL_PROCS, cur_pids) |
| 137 | + |
| 138 | + def _read_control(self, group_name, ctrl_name): |
| 139 | + """Reads a control value for the given group_name (relative to our base path). |
| 140 | + The returned value varies depending on the value content: |
| 141 | + - For a single token value, a string containing that token will be returned. |
| 142 | + - For a single line value with space-seperated tokens, a list of tokens will be returned. |
| 143 | + - For a multi-line value (where each line is a token), a list of tokens will be returned. |
| 144 | + All tokens in the return values are strings. |
| 145 | + A RuntimeError will be raised if the control cannot be read. |
| 146 | + """ |
| 147 | + try: |
| 148 | + with open( |
| 149 | + os.path.join(self._cgroup_path, group_name, ctrl_name), |
| 150 | + encoding="ascii", |
| 151 | + ) as file_in: |
| 152 | + values = [line.strip() for line in file_in.readlines()] |
| 153 | + if " " in values and len(values) == 1: |
| 154 | + values = values[0].split(" ") |
| 155 | + if len(values) == 1: |
| 156 | + values = values[0] |
| 157 | + return values |
| 158 | + except PermissionError as err: |
| 159 | + raise RuntimeError(f"Access denied reading read control '{group_name}/{ctrl_name}'") from err |
| 160 | + |
| 161 | + def _write_control(self, group_name, ctrl_name, value): |
| 162 | + """Writes a control value for a given group_name (relative to our base path). |
| 163 | + The value can be a string or an iterable of strings. The values should not |
| 164 | + contain any whitespace characters. |
| 165 | + A RuntimeError will be raised if the control cannot be set. |
| 166 | + """ |
| 167 | + try: |
| 168 | + ctrl_path = os.path.join(self._cgroup_path, group_name, ctrl_name) |
| 169 | + with open(ctrl_path, "w", encoding="ascii") as file_out: |
| 170 | + if isinstance(value, str): |
| 171 | + value = [value] |
| 172 | + for arg in value: |
| 173 | + file_out.write(f"{arg}\n") |
| 174 | + # Flush is critical here as setting multiple values at the same time may fail |
| 175 | + file_out.flush() |
| 176 | + except PermissionError as err: |
| 177 | + raise RuntimeError(f"Access denied writing control '{group_name}/{ctrl_name}'") from err |
| 178 | + except OSError as err: |
| 179 | + # This generally happens if we're trying to set a value that is |
| 180 | + # considered invalid, for example delegating a controller that isn't enabled |
| 181 | + # in the first place. |
| 182 | + raise RuntimeError(f"Error writing control '{group_name}/{ctrl_name}' = {value}") from err |
| 183 | + |
| 184 | + def _get_oom_count(self, slot_name): |
| 185 | + """Extracts the OOM counter as an int for the given slot. |
| 186 | + Returns an int on success, can return a None if the memory.events |
| 187 | + doesn't contain an oom counter or throws RuntimeError on failure. |
| 188 | + """ |
| 189 | + |
| 190 | + def filt(line): |
| 191 | + """Filter to find the oom counter from a memory.events file.""" |
| 192 | + if line.startswith("oom "): |
| 193 | + return int(line[4:]) |
| 194 | + return False |
| 195 | + |
| 196 | + mem_events = os.path.join(self._cgroup_path, slot_name, self.CTRL_MEM_EVENTS) |
| 197 | + return self._filter_file(mem_events, filt) |
| 198 | + |
| 199 | + def _set_limits(self, group_name, cores=None, memory=None, noswap=False): |
| 200 | + """Sets the limits for an existing group. |
| 201 | + See create_slot for a description of the other parameters. |
| 202 | + This will raise a RuntimeError if appyling any of the limits fail to apply. |
| 203 | + """ |
| 204 | + if cores: |
| 205 | + proc_max = int(cores * self.CPU_WEIGHT) |
| 206 | + self._write_control(group_name, self.CTRL_CPU_MAX, f"{proc_max} {self.CPU_PERIOD}") |
| 207 | + if memory: |
| 208 | + self._write_control(group_name, self.CTRL_MEM_MAX, f"{memory}") |
| 209 | + if noswap: |
| 210 | + self._write_control(group_name, self.CTRL_MEM_SWAP_MAX, "0") |
| 211 | + |
| 212 | + def _prepare(self): |
| 213 | + """Sets up the cgroup tree for the current process. |
| 214 | + Should be called once, before using any of the other functions in this class. |
| 215 | +
|
| 216 | + Note that this function (specifcally the _move_init_procs call) assumes that |
| 217 | + the list of processes is static. If the process list changes while this is running, |
| 218 | + it is likely that this will fail to set things up properly. |
| 219 | + """ |
| 220 | + self._detect_path() |
| 221 | + controllers = self._read_control("", self.CTRL_CONTROLLERS) |
| 222 | + if not controllers: |
| 223 | + raise RuntimeError("No controllers enabled") |
| 224 | + for ctrl in ["cpu", "memory"]: |
| 225 | + if not ctrl in controllers: |
| 226 | + raise RuntimeError(f"{ctrl} controller not enabled") |
| 227 | + self._move_init_procs() |
| 228 | + self._write_control("", self.CTRL_SUBTREE, ["+cpu", "+memory"]) |
| 229 | + self._ready = True |
| 230 | + |
| 231 | + def _create_slot(self, slot_name, cores=None, memory=None, noswap=False): |
| 232 | + """Creates a slot for a job with the given slot_name. |
| 233 | + Cores is a float, number of CPU cores this group may use. |
| 234 | + Memory is a string or int, either a number of bytes to limit the group RSS, |
| 235 | + or a string limit with a unit suffix, e.g. "1G" as supported by the cgroup memory |
| 236 | + controller. |
| 237 | + If noswap is set to true, the swap memory limit will be set to 0; this is mostly |
| 238 | + useful for testing (where the system may swap memory instead of triggering an |
| 239 | + OOM, which may allow a process to use more than the memory limit). |
| 240 | + This will raise a RuntimeError if setting up the slot fails. |
| 241 | + """ |
| 242 | + if not self._ready: |
| 243 | + return |
| 244 | + self._create_group(slot_name) |
| 245 | + self._set_limits(slot_name, cores, memory, noswap) |
| 246 | + |
| 247 | + def _remove_slot(self, slot_name): |
| 248 | + """Removes a slot with the given name. |
| 249 | + Can raise usual filesystem OSError if the slot doesn't exist. |
| 250 | + """ |
| 251 | + if not self._ready: |
| 252 | + return |
| 253 | + self._remove_group(slot_name) |
| 254 | + |
| 255 | + def _setup_subproc(self, slot_name): |
| 256 | + """A subprocess preexec function for setting up cgroups. |
| 257 | + This will move te current process into the given cgroup slot. |
| 258 | + On failure, no error will be reported. |
| 259 | + """ |
| 260 | + # Threading danger! |
| 261 | + # There are potential threading issues with preexec functions |
| 262 | + # They must not hold any locks that the parent process might already |
| 263 | + # be holding, including ones in standard library functions. |
| 264 | + # This function should be kept as minimal as possible. |
| 265 | + try: |
| 266 | + self._write_control(slot_name, self.CTRL_PROCS, f"{os.getpid()}") |
| 267 | + except Exception as err: |
| 268 | + # We can't even really log here as we're in the set-up |
| 269 | + # context of the new proces |
| 270 | + pass |
| 271 | + |
| 272 | + def setUp(self): |
| 273 | + """Creates the base cgroup tree if possible. Should be called once |
| 274 | + per process before using systemCall. |
| 275 | + Returns S_OK/S_ERROR. |
| 276 | + """ |
| 277 | + try: |
| 278 | + self._prepare() |
| 279 | + except Exception as err: |
| 280 | + # The majority of CGroup failures will be RuntimeError |
| 281 | + # However we don't want any unexpected failure to crash the upstream module, |
| 282 | + # We just want to continue without cgroup support instead |
| 283 | + return S_ERROR(str(err)) |
| 284 | + return S_OK() |
| 285 | + |
| 286 | + def systemCall(self, *args, **kwargs): |
| 287 | + """A proxy function for Subprocess.systemCall but will create a cgroup2 slot |
| 288 | + if the functionality is available. An optional ceParameters dictionary |
| 289 | + may be included, which will be searched for specific cgroup memory options. |
| 290 | + Returns the usual S_OK/S_ERROR from Subprocess.systemCall. |
| 291 | + """ |
| 292 | + preexec_fn = None |
| 293 | + slot_name = f"subproc_{os.getpid()}_{self._subproc_num}" |
| 294 | + self._subproc_num += 1 |
| 295 | + if self._ready: |
| 296 | + self.log.info(f"Creating slot cgroup {slot_name}") |
| 297 | + memory = None |
| 298 | + noswap = False |
| 299 | + if "ceParameters" in kwargs: |
| 300 | + memoryMB = int(kwargs["ceParameters"].get("MemoryLimitMB", 0)) |
| 301 | + if memoryMB: |
| 302 | + memory = memoryMB * 1024 * 1024 |
| 303 | + if kwargs["ceParameters"].get("MemoryNoSwap", "no").lower() in ("yes", "true"): |
| 304 | + noswap = True |
| 305 | + try: |
| 306 | + self.log.info(f"CGroup Limits, Mem: {memory}, NoSwap: {noswap}") |
| 307 | + self._create_slot(slot_name, memory=memory, noswap=noswap) |
| 308 | + preexec_fn = functools.partial(CG2Manager._setup_subproc, self, slot_name) |
| 309 | + except Exception as err: |
| 310 | + self.log.warn("Failed to create slot cgroup:", str(err)) |
| 311 | + kwargs["preexec_fn"] = preexec_fn |
| 312 | + kwargs.pop("ceParameters", None) |
| 313 | + res = Subprocess.systemCall(*args, **kwargs) |
| 314 | + if self._ready: |
| 315 | + self.log.info(f"Removing slot cgroup {slot_name}") |
| 316 | + try: |
| 317 | + oom_count = self._get_oom_count(slot_name) |
| 318 | + if oom_count: |
| 319 | + # Child process triggered an OOM |
| 320 | + # We can't readily report this upstream (child process will probably |
| 321 | + # fail with an error code), so just log it and continue |
| 322 | + self.log.info(f"OOM detected from child process (slot {slot_name})") |
| 323 | + self._remove_slot(slot_name) |
| 324 | + except Exception as err: |
| 325 | + self.log.warn(f"Failed to delete slot {slot_name} cgroup:", str(err)) |
| 326 | + return res |
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