【发布时间】：2013-02-09 15:37:36
【问题描述】：
为什么 OS X 10.6.8 中的 host_statistics64()（我不知道其他版本是否有这个问题）返回的免费、活动、非活动和有线内存的计数加起来不等于总数内存？为什么它缺少不一致的页数？
以下输出表示十秒内未分类为空闲、活动、非活动或有线的页面数（大约每秒采样一次）。
458
243
153
199
357
140
304
93
181
224
产生上述数字的代码是：
#include <stdio.h>
#include <mach/mach.h>
#include <mach/vm_statistics.h>
#include <sys/types.h>
#include <sys/sysctl.h>
#include <unistd.h>
#include <string.h>
int main(int argc, char** argv) {
struct vm_statistics64 stats;
mach_port_t host = mach_host_self();
natural_t count = HOST_VM_INFO64_COUNT;
natural_t missing = 0;
int debug = argc == 2 ? !strcmp(argv[1], "-v") : 0;
kern_return_t ret;
int mib[2];
long ram;
natural_t pages;
size_t length;
int i;
mib[0] = CTL_HW;
mib[1] = HW_MEMSIZE;
length = sizeof(long);
sysctl(mib, 2, &ram, &length, NULL, 0);
pages = ram / getpagesize();
for (i = 0; i < 10; i++) {
if ((ret = host_statistics64(host, HOST_VM_INFO64, (host_info64_t)&stats, &count)) != KERN_SUCCESS) {
printf("oops\n");
return 1;
}
/* updated for 10.9 */
missing = pages - (
stats.free_count +
stats.active_count +
stats.inactive_count +
stats.wire_count +
stats.compressor_page_count
);
if (debug) {
printf(
"%11d pages (# of pages)\n"
"%11d free_count (# of pages free) \n"
"%11d active_count (# of pages active) \n"
"%11d inactive_count (# of pages inactive) \n"
"%11d wire_count (# of pages wired down) \n"
"%11lld zero_fill_count (# of zero fill pages) \n"
"%11lld reactivations (# of pages reactivated) \n"
"%11lld pageins (# of pageins) \n"
"%11lld pageouts (# of pageouts) \n"
"%11lld faults (# of faults) \n"
"%11lld cow_faults (# of copy-on-writes) \n"
"%11lld lookups (object cache lookups) \n"
"%11lld hits (object cache hits) \n"
"%11lld purges (# of pages purged) \n"
"%11d purgeable_count (# of pages purgeable) \n"
"%11d speculative_count (# of pages speculative (also counted in free_count)) \n"
"%11lld decompressions (# of pages decompressed) \n"
"%11lld compressions (# of pages compressed) \n"
"%11lld swapins (# of pages swapped in (via compression segments)) \n"
"%11lld swapouts (# of pages swapped out (via compression segments)) \n"
"%11d compressor_page_count (# of pages used by the compressed pager to hold all the compressed data) \n"
"%11d throttled_count (# of pages throttled) \n"
"%11d external_page_count (# of pages that are file-backed (non-swap)) \n"
"%11d internal_page_count (# of pages that are anonymous) \n"
"%11lld total_uncompressed_pages_in_compressor (# of pages (uncompressed) held within the compressor.) \n",
pages, stats.free_count, stats.active_count, stats.inactive_count,
stats.wire_count, stats.zero_fill_count, stats.reactivations,
stats.pageins, stats.pageouts, stats.faults, stats.cow_faults,
stats.lookups, stats.hits, stats.purges, stats.purgeable_count,
stats.speculative_count, stats.decompressions, stats.compressions,
stats.swapins, stats.swapouts, stats.compressor_page_count,
stats.throttled_count, stats.external_page_count,
stats.internal_page_count, stats.total_uncompressed_pages_in_compressor
);
}
printf("%i\n", missing);
sleep(1);
}
return 0;
}
【问题讨论】：
-
vm_stat，使用相同的代码，有同样的不完全加法问题。所以，这不是你的代码本身的问题。 -
使用 ML 和 8 GB RAM，缺少的部分更大（大约 2400）。
-
看看opensource.apple.com/source/top/top-73/libtop.c，里面好像有一些特殊的计算。
-
@nneonneo 哦，我知道。我试图弄清楚为什么
vm_stat给我的数据不好。 -
@patrix 我不知道这是否是巧合，但这似乎是正确的。我最糟糕的情况是丢失了 500 到 600 页，而我有两个 CPU。如果我们将其扩展到 8 个 CPU，您会看到 2000 到 2400 个页面丢失。如果是这种情况，那么这些页面当前没有被任何 CPU 声明；这意味着它们很可能正在 CPU 之间传输。