gh-132917: Check resident set size (RSS) before GC trigger. (gh-133399)

For the free-threaded build, check the process resident set size (RSS)
increase before triggering a full automatic garbage collection.  If the RSS
has not increased 10% since the last collection then it is deferred.

Author: nascheme

Doc/library/gc.rst

@@ -128,6 +128,11 @@ The :mod:`gc` module provides the following functions:
    starts. For each collection, all the objects in the young generation and some
    fraction of the old generation is collected.
 
+   In the free-threaded build, the increase in process resident set size (RSS)
+   is also checked before running the collector.  If the RSS has not increased
+   by 10% since the last collection and the net number of object allocations
+   has not exceeded 40 times *threshold0*, the collection is not run.
+
    The fraction of the old generation that is collected is **inversely** proportional
    to *threshold1*. The larger *threshold1* is, the slower objects in the old generation
    are collected.

Include/internal/pycore_interp_structs.h

@@ -245,6 +245,16 @@ struct _gc_runtime_state {
 
     /* True if gc.freeze() has been used. */
     int freeze_active;
+
+    /* Resident set size (RSS) of the process after last GC. */
+    Py_ssize_t last_rss;
+
+    /* This accumulates the new object count whenever collection is deferred
+       due to the RSS increase condition not being meet.  Reset on collection. */
+    Py_ssize_t deferred_count;
+
+    /* Mutex held for gc_should_collect_rss(). */
+    PyMutex mutex;
 #endif
 };
 

Misc/NEWS.d/next/Core_and_Builtins/2025-05-04-14-47-26.gh-issue-132917.DrEU1y.rst

@@ -0,0 +1,3 @@
+For the free-threaded build, check the process resident set size (RSS)
+increase before triggering a full automatic garbage collection.  If the RSS
+has not increased 10% since the last collection then it is deferred.

Python/gc_free_threading.c

@@ -17,6 +17,29 @@
 
 #include "pydtrace.h"
 
+// Platform-specific includes for get_current_rss().
+#ifdef _WIN32
+    #include <windows.h>
+    #include <psapi.h> // For GetProcessMemoryInfo
+#elif defined(__linux__)
+    #include <unistd.h> // For sysconf, getpid
+#elif defined(__APPLE__)
+    #include <mach/mach.h>
+    #include <unistd.h> // For sysconf, getpid
+#elif defined(__FreeBSD__)
+    #include <sys/types.h>
+    #include <sys/sysctl.h>
+    #include <sys/user.h> // Requires sys/user.h for kinfo_proc definition
+    #include <kvm.h>
+    #include <unistd.h> // For sysconf, getpid
+    #include <fcntl.h> // For O_RDONLY
+    #include <limits.h> // For _POSIX2_LINE_MAX
+#elif defined(__OpenBSD__)
+    #include <sys/types.h>
+    #include <sys/sysctl.h>
+    #include <sys/user.h> // For kinfo_proc
+    #include <unistd.h> // For sysconf, getpid
+#endif
 
 // enable the "mark alive" pass of GC
 #define GC_ENABLE_MARK_ALIVE 1
@@ -1878,6 +1901,180 @@ cleanup_worklist(struct worklist *worklist)
     }
 }
 
+// Return the current resident set size (RSS) of the process, in units of KB.
+// Returns -1 if this operation is not supported or on failure.
+static Py_ssize_t
+get_current_rss(void)
+{
+#ifdef _WIN32
+    // Windows implementation using GetProcessMemoryInfo
+    PROCESS_MEMORY_COUNTERS pmc;
+    HANDLE hProcess = GetCurrentProcess();
+    if (NULL == hProcess) {
+        // Should not happen for the current process
+        return -1;
+    }
+
+    // GetProcessMemoryInfo returns non-zero on success
+    if (GetProcessMemoryInfo(hProcess, &pmc, sizeof(pmc))) {
+        // pmc.WorkingSetSize is in bytes. Convert to KB.
+        return (Py_ssize_t)(pmc.WorkingSetSize / 1024);
+    }
+    else {
+        return -1;
+    }
+
+#elif __linux__
+    // Linux implementation using /proc/self/statm
+    long page_size_bytes = sysconf(_SC_PAGE_SIZE);
+    if (page_size_bytes <= 0) {
+        return -1;
+    }
+
+    FILE *fp = fopen("/proc/self/statm", "r");
+    if (fp == NULL) {
+        return -1;
+    }
+
+    // Second number is resident size in pages
+    long rss_pages;
+    if (fscanf(fp, "%*d %ld", &rss_pages) != 1) {
+        fclose(fp);
+        return -1;
+    }
+    fclose(fp);
+
+    // Sanity check
+    if (rss_pages < 0 || rss_pages > 1000000000) {
+        return -1;
+    }
+
+    // Convert unit to KB
+    return (Py_ssize_t)rss_pages * (page_size_bytes / 1024);
+
+#elif defined(__APPLE__)
+    // --- MacOS (Darwin) ---
+    mach_msg_type_number_t count = MACH_TASK_BASIC_INFO_COUNT;
+    mach_task_basic_info_data_t info;
+    kern_return_t kerr;
+
+    kerr = task_info(mach_task_self(), MACH_TASK_BASIC_INFO, (task_info_t)&info, &count);
+    if (kerr != KERN_SUCCESS) {
+        return -1;
+    }
+    // info.resident_size is in bytes. Convert to KB.
+    return (Py_ssize_t)(info.resident_size / 1024);
+
+#elif defined(__FreeBSD__)
+    long page_size_kb = sysconf(_SC_PAGESIZE) / 1024;
+    if (page_size_kb <= 0) {
+        return -1;
+    }
+
+    // Using /dev/null for vmcore avoids needing dump file.
+    // NULL for kernel file uses running kernel.
+    char errbuf[_POSIX2_LINE_MAX]; // For kvm error messages
+    kvm_t *kd = kvm_openfiles(NULL, "/dev/null", NULL, O_RDONLY, errbuf);
+    if (kd == NULL) {
+        return -1;
+    }
+
+    // KERN_PROC_PID filters for the specific process ID
+    // n_procs will contain the number of processes returned (should be 1 or 0)
+    pid_t pid = getpid();
+    int n_procs;
+    struct kinfo_proc *kp = kvm_getprocs(kd, KERN_PROC_PID, pid, &n_procs);
+    if (kp == NULL) {
+        kvm_close(kd);
+        return -1;
+    }
+
+    Py_ssize_t rss_kb = -1;
+    if (n_procs > 0) {
+        // kp[0] contains the info for our process
+        // ki_rssize is in pages. Convert to KB.
+        rss_kb = (Py_ssize_t)kp->ki_rssize * page_size_kb;
+    }
+    else {
+        // Process with PID not found, shouldn't happen for self.
+        rss_kb = -1;
+    }
+
+    kvm_close(kd);
+    return rss_kb;
+
+#elif defined(__OpenBSD__)
+    long page_size_kb = sysconf(_SC_PAGESIZE) / 1024;
+    if (page_size_kb <= 0) {
+        return -1;
+    }
+
+    struct kinfo_proc kp;
+    pid_t pid = getpid();
+    int mib[6];
+    size_t len = sizeof(kp);
+
+    mib[0] = CTL_KERN;
+    mib[1] = KERN_PROC;
+    mib[2] = KERN_PROC_PID;
+    mib[3] = pid;
+    mib[4] = sizeof(struct kinfo_proc); // size of the structure we want
+    mib[5] = 1;                         // want 1 structure back
+    if (sysctl(mib, 6, &kp, &len, NULL, 0) == -1) {
+         return -1;
+    }
+
+    if (len > 0) {
+        // p_vm_rssize is in pages on OpenBSD. Convert to KB.
+        return (Py_ssize_t)kp.p_vm_rssize * page_size_kb;
+    }
+    else {
+        // Process info not returned
+        return -1;
+    }
+#else
+    // Unsupported platform
+    return -1;
+#endif
+}
+
+static bool
+gc_should_collect_rss(GCState *gcstate)
+{
+    Py_ssize_t rss = get_current_rss();
+    if (rss < 0) {
+        // Reading RSS is not support or failed.
+        return true;
+    }
+    int threshold = gcstate->young.threshold;
+    Py_ssize_t deferred = _Py_atomic_load_ssize_relaxed(&gcstate->deferred_count);
+    if (deferred > threshold * 40) {
+        // Too many new container objects since last GC, even though RSS
+        // might not have increased much.  This is intended to avoid resource
+        // exhaustion if some objects consume resources but don't result in a
+        // RSS increase.  We use 40x as the factor here because older versions
+        // of Python would do full collections after roughly every 70,000 new
+        // container objects.
+        return true;
+    }
+    Py_ssize_t last_rss = gcstate->last_rss;
+    Py_ssize_t rss_threshold = Py_MAX(last_rss / 10, 128);
+    if ((rss - last_rss) > rss_threshold) {
+        // The RSS has increased too much, do a collection.
+        return true;
+    }
+    else {
+        // The RSS has not increased enough, defer the collection and clear
+        // the young object count so we don't check RSS again on the next call
+        // to gc_should_collect().
+        PyMutex_Lock(&gcstate->mutex);
+        gcstate->deferred_count += gcstate->young.count;
+        gcstate->young.count = 0;
+        PyMutex_Unlock(&gcstate->mutex);
+        return false;
+    }
+}
+
 static bool
 gc_should_collect(GCState *gcstate)
 {
@@ -1887,11 +2084,17 @@ gc_should_collect(GCState *gcstate)
     if (count <= threshold || threshold == 0 || !gc_enabled) {
         return false;
     }
-    // Avoid quadratic behavior by scaling threshold to the number of live
-    // objects. A few tests rely on immediate scheduling of the GC so we ignore
-    // the scaled threshold if generations[1].threshold is set to zero.
-    return (count > gcstate->long_lived_total / 4 ||
-            gcstate->old[0].threshold == 0);
+    if (gcstate->old[0].threshold == 0) {
+        // A few tests rely on immediate scheduling of the GC so we ignore the
+        // extra conditions if generations[1].threshold is set to zero.
+        return true;
+    }
+    if (count < gcstate->long_lived_total / 4) {
+        // Avoid quadratic behavior by scaling threshold to the number of live
+        // objects.
+        return false;
+    }
+    return gc_should_collect_rss(gcstate);
 }
 
 static void
@@ -1940,6 +2143,7 @@ gc_collect_internal(PyInterpreterState *interp, struct collection_state *state,
     }
 
     state->gcstate->young.count = 0;
+    state->gcstate->deferred_count = 0;
     for (int i = 1; i <= generation; ++i) {
         state->gcstate->old[i-1].count = 0;
     }
@@ -2033,6 +2237,9 @@ gc_collect_internal(PyInterpreterState *interp, struct collection_state *state,
     // to be freed.
     delete_garbage(state);
 
+    // Store the current RSS, possibly smaller now that we deleted garbage.
+    state->gcstate->last_rss = get_current_rss();
+
     // Append objects with legacy finalizers to the "gc.garbage" list.
     handle_legacy_finalizers(state);
 }