这是一种肮脏的黑客行为,最适合特权进程或具有高权限的系统。RLIMIT_MEMLOCK
,但是……一个mlock
and munlock
配对将达到您正在寻找的效果。
例如,给出以下测试程序:
# compile with (for e.g.,): cc -O1 -Wall pagefaults.c -o pagefaults
#include <stdlib.h>
#include <stdio.h>
#include <err.h>
#include <sys/mman.h>
#define DEFAULT_SIZE (40 * 1024 * 1024)
#define PG_SIZE 4096
void failcheck(int ret, const char* what) {
if (ret) {
err(EXIT_FAILURE, "%s failed", what);
} else {
printf("%s OK\n", what);
}
}
int main(int argc, char **argv) {
size_t size = (argc == 2 ? atol(argv[1]) : DEFAULT_SIZE);
char *mem = malloc(size);
if (getenv("DO_MADVISE")) {
failcheck(madvise(mem, size, MADV_WILLNEED), "madvise");
}
if (getenv("DO_MLOCK")) {
failcheck(mlock(mem, size), "mlock");
failcheck(munlock(mem, size), "munlock");
}
for (volatile char *p = mem; p < mem + size; p += PG_SIZE) {
*p = 'z';
}
printf("size: %6.2f MiB, pages touched: %zu\npoitner value : %p\n",
size / 1024. / 1024., size / PG_SIZE, mem);
}
以 root 身份运行 1 GB 区域并计算页面错误perf
结果是:
$ perf stat ./pagefaults 1000000000
size: 953.67 MiB, pages touched: 244140
poitner value : 0x7f2fc2584010
Performance counter stats for './pagefaults 1000000000':
352.474676 task-clock (msec) # 0.999 CPUs utilized
2 context-switches # 0.006 K/sec
0 cpu-migrations # 0.000 K/sec
244,189 page-faults # 0.693 M/sec
914,276,474 cycles # 2.594 GHz
703,359,688 instructions # 0.77 insn per cycle
117,710,381 branches # 333.954 M/sec
447,022 branch-misses # 0.38% of all branches
0.352814087 seconds time elapsed
但是,如果您运行前缀为DO_MLOCK=1
, 你得到:
sudo DO_MLOCK=1 perf stat ./pagefaults 1000000000
mlock OK
munlock OK
size: 953.67 MiB, pages touched: 244140
poitner value : 0x7f8047f6b010
Performance counter stats for './pagefaults 1000000000':
240.236189 task-clock (msec) # 0.999 CPUs utilized
0 context-switches # 0.000 K/sec
0 cpu-migrations # 0.000 K/sec
49 page-faults # 0.204 K/sec
623,152,764 cycles # 2.594 GHz
959,640,219 instructions # 1.54 insn per cycle
150,713,144 branches # 627.354 M/sec
484,400 branch-misses # 0.32% of all branches
0.240538327 seconds time elapsed
请注意,页面错误数量已从 244,189 减少到 49,并且速度提高了 1.46 倍。绝大多数时间仍然花费在内核中,因此如果不需要同时调用两者,这可能会快得多mlock
and munlock
也可能是因为语义mlock
超过了需要的数量。
对于非特权进程,您可能会遇到RLIMIT_MEMLOCK
如果您尝试一次执行一个大区域(在我的 Ubuntu 系统上,它设置为 64 Kib),但您可以循环调用该区域mlock(); munlock()
在较小的区域上。