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Clean up cgroup handling in getMaxCPU()

Browse source 
Also, don't assume in LocalDerivationGoal that cgroups are mounted on
/sys/fs/cgroup.
This commit is contained in:
Eelco Dolstra 2022-12-02 12:57:41 +01:00
parent 1211e59a03
commit 1e6a5d1ff6
4 changed files with 39 additions and 35 deletions
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6
src/libstore/build/local-derivation-goal.cc
View file

@ -409,12 +409,16 @@ void LocalDerivationGoal::startBuilder()
#if __linux__
settings.requireExperimentalFeature(Xp::Cgroups);
auto cgroupFS = getCgroupFS();
if (!cgroupFS)
throw Error("cannot determine the cgroups file system");
auto ourCgroups = getCgroups("/proc/self/cgroup");
auto ourCgroup = ourCgroups[""];
if (ourCgroup == "")
throw Error("cannot determine cgroup name from /proc/self/cgroup");
auto ourCgroupPath = canonPath("/sys/fs/cgroup/" + ourCgroup);
auto ourCgroupPath = canonPath(*cgroupFS + "/" + ourCgroup);
if (!pathExists(ourCgroupPath))
throw Error("expected cgroup directory '%s'", ourCgroupPath);

17
src/libutil/cgroup.cc
View file

@ -2,6 +2,7 @@
#include "cgroup.hh"
#include "util.hh"
#include "finally.hh"
#include <chrono>
#include <cmath>
@ -10,9 +11,25 @@
#include <thread>
#include <dirent.h>
#include <mntent.h>
namespace nix {
std::optional<Path> getCgroupFS()
{
static auto res = [&]() -> std::optional<Path> {
auto fp = fopen("/proc/mounts", "r");
if (!fp) return std::nullopt;
Finally delFP = [&]() { fclose(fp); };
while (auto ent = getmntent(fp))
if (std::string_view(ent->mnt_type) == "cgroup2")
return ent->mnt_dir;
return std::nullopt;
}();
return res;
}
// FIXME: obsolete, check for cgroup2
std::map<std::string, std::string> getCgroups(const Path & cgroupFile)
{

2
src/libutil/cgroup.hh
View file

@ -9,6 +9,8 @@
namespace nix {
std::optional<Path> getCgroupFS();
std::map<std::string, std::string> getCgroups(const Path & cgroupFile);
struct CgroupStats

49
src/libutil/util.cc
View file

@ -2,6 +2,7 @@
#include "sync.hh"
#include "finally.hh"
#include "serialise.hh"
#include "cgroup.hh"
#include <array>
#include <cctype>
@ -36,7 +37,6 @@
#include <sys/prctl.h>
#include <sys/resource.h>
#include <mntent.h>
#include <cmath>
#endif
@ -727,43 +727,24 @@ unsigned int getMaxCPU()
{
#if __linux__
try {
FILE *fp = fopen("/proc/mounts", "r");
if (!fp)
return 0;
auto cgroupFS = getCgroupFS();
if (!cgroupFS) return 0;
Strings cgPathParts;
if (!pathExists("/proc/self/cgroup")) return 0;
struct mntent *ent;
while ((ent = getmntent(fp))) {
std::string mountType, mountPath;
auto cgroups = getCgroups("/proc/self/cgroup");
auto cgroup = cgroups[""];
if (cgroup == "") return 0;
mountType = ent->mnt_type;
mountPath = ent->mnt_dir;
auto cpuFile = *cgroupFS + "/" + cgroup + "/cpu.max";
if (mountType == "cgroup2") {
cgPathParts.push_back(mountPath);
break;
}
}
fclose(fp);
if (cgPathParts.size() > 0 && pathExists("/proc/self/cgroup")) {
std::string currentCgroup = readFile("/proc/self/cgroup");
Strings cgValues = tokenizeString<Strings>(currentCgroup, ":");
cgPathParts.push_back(trim(cgValues.back(), "\n"));
cgPathParts.push_back("cpu.max");
std::string fullCgPath = canonPath(concatStringsSep("/", cgPathParts));
if (pathExists(fullCgPath)) {
std::string cpuMax = readFile(fullCgPath);
std::vector<std::string> cpuMaxParts = tokenizeString<std::vector<std::string>>(cpuMax, " ");
std::string quota = cpuMaxParts[0];
std::string period = trim(cpuMaxParts[1], "\n");
if (quota != "max")
return std::ceil(std::stoi(quota) / std::stof(period));
}
if (pathExists(cpuFile)) {
auto cpuMax = readFile(cpuFile);
auto cpuMaxParts = tokenizeString<std::vector<std::string>>(cpuMax, " \n");
auto quota = cpuMaxParts[0];
auto period = cpuMaxParts[1];
if (quota != "max")
return std::ceil(std::stoi(quota) / std::stof(period));
}
} catch (Error &) { ignoreException(); }
#endif