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Merge pull request #479 from devnexen/overcommit_if_the_system_approves

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proposal to not overcommit page unconditionally on Linux and FreeBSD,
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Daan 2021-10-27 17:24:57 -07:00 committed by GitHub
commit 88d5349d47
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1 changed files with 34 additions and 1 deletions
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35
src/os.c
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@ -39,6 +39,8 @@ terms of the MIT license. A copy of the license can be found in the file
#include <unistd.h> // sysconf
#if defined(__linux__)
#include <features.h>
#include <fcntl.h>
#include <stdlib.h>
#if defined(__GLIBC__)
#include <linux/mman.h> // linux mmap flags
#else
@ -96,6 +98,9 @@ static size_t os_alloc_granularity = 4096;
// if non-zero, use large page allocation
static size_t large_os_page_size = 0;
// if non-zero, enable page overcommit
static int os_overcommit = 0;
// OS (small) page size
size_t _mi_os_page_size() {
return os_page_size;
@ -231,6 +236,31 @@ void _mi_os_init() {
os_alloc_granularity = os_page_size;
}
large_os_page_size = 2*MiB; // TODO: can we query the OS for this?
#if defined(__linux__)
int fd = open("/proc/sys/vm/overcommit_memory", O_RDONLY);
if (fd != -1) {
char buf[1] = {0};
if (read(fd, buf, sizeof(buf)) == sizeof(buf)) {
switch (buf[0]) {
case '0': // heuristic mode
case '1': // always
os_overcommit = 1;
break;
default: // never regardless
os_overcommit = 0;
}
}
close(fd);
}
#elif defined(__FreeBSD__)
int val = 0;
size_t olen = sizeof(val);
if (sysctlbyname("vm.overcommit", &val, &olen, NULL, 0) == 0) {
os_overcommit = val;
}
#elif defined(__NetBSD__) || defined(__HAIKU__)
os_overcommit = 1;
#endif
}
#endif
@ -406,8 +436,11 @@ static void* mi_unix_mmap(void* addr, size_t size, size_t try_alignment, int pro
#if !defined(MAP_NORESERVE)
#define MAP_NORESERVE 0
#endif
int flags = MAP_PRIVATE | MAP_ANONYMOUS | MAP_NORESERVE;
int flags = MAP_PRIVATE | MAP_ANONYMOUS;
int fd = -1;
if (os_overcommit) {
flags |= MAP_NORESERVE;
}
#if defined(MAP_ALIGNED) // BSD
if (try_alignment > 0) {
size_t n = mi_bsr(try_alignment);