Become a memory accounting amateur

2026-01-27 12:04:27 +01:00 · 2019-08-27 00:00:00 +00:00
parent 1e969e832f
commit efc4205416
10 changed files with 411 additions and 65 deletions
--- a/userland/linux/mmap_anonymous_touch.c
+++ b/userland/linux/mmap_anonymous_touch.c
@@ -0,0 +1,125 @@
+/* https://cirosantilli.com/linux-kernel-module-cheat#malloc-maximum-size
+ *
+ * mmap memory, then write something to each page to ensure it is not just virtual.
+ * We want to meet the OOM.
+ *
+ * ./prog [nbytes [print_interval]]
+ */
+
+#define _GNU_SOURCE
+#include <assert.h>
+#include <inttypes.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/mman.h>
+#include <unistd.h>
+
+typedef struct {
+    unsigned long size,resident,share,text,lib,data,dt;
+} ProcStatm;
+
+/* https://stackoverflow.com/questions/1558402/memory-usage-of-current-process-in-c/7212248#7212248 */
+void ProcStat_init(ProcStatm *result) {
+    const char* statm_path = "/proc/self/statm";
+    FILE *f = fopen(statm_path, "r");
+    if(!f) {
+        perror(statm_path);
+        abort();
+    }
+    if(7 != fscanf(
+        f,
+        "%ld %ld %ld %ld %ld %ld %ld",
+        &(result->size),
+        &(result->resident),
+        &(result->share),
+        &(result->text),
+        &(result->lib),
+        &(result->data),
+        &(result->dt)
+    )) {
+        perror(statm_path);
+        abort();
+    }
+    fclose(f);
+}
+
+int main(int argc, char **argv) {
+    ProcStatm proc_statm;
+    char *base, *p;
+    char system_cmd[1024];
+    long page_size;
+    size_t i, nbytes, print_interval, bytes_since_last_print;
+    int snprintf_return;
+
+    /* Decide how many ints to allocate. */
+    if (argc < 2) {
+        nbytes = 0x10000;
+    } else {
+        nbytes = strtoull(argv[1], NULL, 0);
+    }
+    if (argc < 3) {
+        print_interval = 0x1000;
+    } else {
+        print_interval = strtoull(argv[2], NULL, 0);
+    }
+    page_size = sysconf(_SC_PAGESIZE);
+
+    /* Allocate the memory. */
+    base = mmap(
+        NULL,
+        nbytes,
+        PROT_READ | PROT_WRITE,
+        MAP_SHARED | MAP_ANONYMOUS,
+        -1,
+        0
+    );
+    if (base == MAP_FAILED) {
+        perror("mmap");
+        exit(EXIT_FAILURE);
+    }
+
+    /* Write to all the allocated pages. */
+    i = 0;
+    p = base;
+    bytes_since_last_print = 0;
+    /* Produce the ps command that lists only our VSZ and RSS. */
+    snprintf_return = snprintf(
+        system_cmd,
+        sizeof(system_cmd),
+        "ps -o pid,vsz,rss | awk '{if (NR == 1 || $1 == \"%ju\") print}'",
+        (uintmax_t)getpid()
+    );
+    assert(snprintf_return >= 0);
+    assert((size_t)snprintf_return < sizeof(system_cmd));
+    bytes_since_last_print = print_interval;
+    do {
+        /* Modify a byte in the page. */
+        *p = i;
+        p += page_size;
+        bytes_since_last_print += page_size;
+        /* Print process memory usage every print_interval bytes.
+         * We count memory using a few techniques from:
+         * https://stackoverflow.com/questions/1558402/memory-usage-of-current-process-in-c */
+        if (bytes_since_last_print > print_interval) {
+            bytes_since_last_print -= print_interval;
+            printf("extra_memory_committed %lu KiB\n", (i * page_size) / 1024);
+            ProcStat_init(&proc_statm);
+            /* Check /proc/self/statm */
+            printf(
+                "/proc/self/statm size resident %lu %lu KiB\n",
+                (proc_statm.size * page_size) / 1024,
+                (proc_statm.resident * page_size) / 1024
+            );
+            /* Check ps. */
+            puts(system_cmd);
+            system(system_cmd);
+            puts("");
+        }
+        i++;
+    } while (p < base + nbytes);
+
+    /* Cleanup. */
+    munmap(base, nbytes);
+    return EXIT_SUCCESS;
+}