为什么OS X 10.6.8中的host_statistics64（）（我不知道其他版本是否存在此问题）返回的计数为免费，活动，非活动和有线内存，但总计不超过内存？为什么它缺少不一致的页数？
以下输出表示十秒钟内未分类为空闲，活动，非活动或有线的页面数量（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;
}
答案 0 :(得分：9)
TL; DR：
host_statistics64()从不同来源获取可能需要花费时间并且可能产生不一致结果的信息。 host_statistics64()通过名称为vm_page_foo_count的变量获取一些信息。但并非所有这些变量都被考虑在内，例如vm_page_stolen_count不是。/usr/bin/top将被盗网页添加到有线网页的数量中。这表示在计算页数时应考虑这些页面。备注
/usr/bin/vm_stat基本相同，host_statistics64()只是host_statistics()（和host_statistics64()）的包装。可以在此处找到相应的源代码：system_cmds-496/vm_stat.tproj/vm_stat.c。 host_statistics64()如何适应XNU以及它如何运作？
正如威德利所知，OS X内核被称为 XNU（ X NU IS N OT U NIX）和＆＃34;是一个混合内核，将Carnegie Mellon大学开发的Mach内核与FreeBSD和C ++ API的组件相结合，用于编写名为IOKit的驱动程序。＆＃34; （https://github.com/opensource-apple/xnu/blob/10.12/README.md）< / p>
虚拟内存管理（VM）是 Mach 的一部分，因此kern_return_t
host_statistics64(host_t host, host_flavor_t flavor, host_info64_t info, mach_msg_type_number_t * count);
位于此处。让我们仔细看看xnu-3789.51.2/osfmk/kern/host.c中包含的实现。
功能签名是
[...]
processor_t processor;
vm_statistics64_t stat;
vm_statistics64_data_t host_vm_stat;
mach_msg_type_number_t original_count;
unsigned int local_q_internal_count;
unsigned int local_q_external_count;
[...]
processor = processor_list;
stat = &PROCESSOR_DATA(processor, vm_stat);
host_vm_stat = *stat;
if (processor_count > 1) {
simple_lock(&processor_list_lock);
while ((processor = processor->processor_list) != NULL) {
stat = &PROCESSOR_DATA(processor, vm_stat);
host_vm_stat.zero_fill_count += stat->zero_fill_count;
host_vm_stat.reactivations += stat->reactivations;
host_vm_stat.pageins += stat->pageins;
host_vm_stat.pageouts += stat->pageouts;
host_vm_stat.faults += stat->faults;
host_vm_stat.cow_faults += stat->cow_faults;
host_vm_stat.lookups += stat->lookups;
host_vm_stat.hits += stat->hits;
host_vm_stat.compressions += stat->compressions;
host_vm_stat.decompressions += stat->decompressions;
host_vm_stat.swapins += stat->swapins;
host_vm_stat.swapouts += stat->swapouts;
}
simple_unlock(&processor_list_lock);
}
[...]
第一个相关的行是
host_vm_stat我们得到的vm_statistics64_data_t类型为typedef struct vm_statistics64。您可以在xnu-3789.51.2/osfmk/mach/vm_statistics.h中看到这只是PROCESSOR_DATA()。我们从xnu-3789.51.2/osfmk/kern/processor_data.h中定义的makro host_vm_stat获取处理器信息。我们通过简单地添加相关数字来填充zero_fill_count，同时循环遍历所有处理器。
正如您所看到的，我们会找到一些众所周知的统计信息，例如compressions或host_statistics64()，但并非stat = (vm_statistics64_t)info;
stat->free_count = vm_page_free_count + vm_page_speculative_count;
stat->active_count = vm_page_active_count;
[...]
stat->inactive_count = vm_page_inactive_count;
stat->wire_count = vm_page_wire_count + vm_page_throttled_count + vm_lopage_free_count;
stat->zero_fill_count = host_vm_stat.zero_fill_count;
stat->reactivations = host_vm_stat.reactivations;
stat->pageins = host_vm_stat.pageins;
stat->pageouts = host_vm_stat.pageouts;
stat->faults = host_vm_stat.faults;
stat->cow_faults = host_vm_stat.cow_faults;
stat->lookups = host_vm_stat.lookups;
stat->hits = host_vm_stat.hits;
stat->purgeable_count = vm_page_purgeable_count;
stat->purges = vm_page_purged_count;
stat->speculative_count = vm_page_speculative_count;
涵盖的所有统计信息。
下一个相关的行是：
stat我们重用free_count并将其作为输出结构。然后，我们使用unsigned long和vm_page_free_count两个vm_page_speculative_count的总和填充vm_page_foo_count。我们以相同的方式收集其他剩余数据（通过使用名为host_vm_stat的变量）或从上面填写的vm_page_foo_count中获取统计数据。
1。结论我们从不同来源收集数据。来自处理器信息或来自名为vm_page_foo_count的变量。这需要花费时间，并且可能以某种不一致的方式结束，因为VM是一个非常快速且持续的过程。
让我们仔细研究已经提到的变量extern
unsigned int vm_page_free_count; /* How many pages are free? (sum of all colors) */
extern
unsigned int vm_page_active_count; /* How many pages are active? */
extern
unsigned int vm_page_inactive_count; /* How many pages are inactive? */
#if CONFIG_SECLUDED_MEMORY
extern
unsigned int vm_page_secluded_count; /* How many pages are secluded? */
extern
unsigned int vm_page_secluded_count_free;
extern
unsigned int vm_page_secluded_count_inuse;
#endif /* CONFIG_SECLUDED_MEMORY */
extern
unsigned int vm_page_cleaned_count; /* How many pages are in the clean queue? */
extern
unsigned int vm_page_throttled_count;/* How many inactives are throttled */
extern
unsigned int vm_page_speculative_count; /* How many speculative pages are unclaimed? */
extern unsigned int vm_page_pageable_internal_count;
extern unsigned int vm_page_pageable_external_count;
extern
unsigned int vm_page_xpmapped_external_count; /* How many pages are mapped executable? */
extern
unsigned int vm_page_external_count; /* How many pages are file-backed? */
extern
unsigned int vm_page_internal_count; /* How many pages are anonymous? */
extern
unsigned int vm_page_wire_count; /* How many pages are wired? */
extern
unsigned int vm_page_wire_count_initial; /* How many pages wired at startup */
extern
unsigned int vm_page_free_target; /* How many do we want free? */
extern
unsigned int vm_page_free_min; /* When to wakeup pageout */
extern
unsigned int vm_page_throttle_limit; /* When to throttle new page creation */
extern
uint32_t vm_page_creation_throttle; /* When to throttle new page creation */
extern
unsigned int vm_page_inactive_target;/* How many do we want inactive? */
#if CONFIG_SECLUDED_MEMORY
extern
unsigned int vm_page_secluded_target;/* How many do we want secluded? */
#endif /* CONFIG_SECLUDED_MEMORY */
extern
unsigned int vm_page_anonymous_min; /* When it's ok to pre-clean */
extern
unsigned int vm_page_inactive_min; /* When to wakeup pageout */
extern
unsigned int vm_page_free_reserved; /* How many pages reserved to do pageout */
extern
unsigned int vm_page_throttle_count; /* Count of page allocations throttled */
extern
unsigned int vm_page_gobble_count;
extern
unsigned int vm_page_stolen_count; /* Count of stolen pages not acccounted in zones */
[...]
extern
unsigned int vm_page_purgeable_count;/* How many pages are purgeable now ? */
extern
unsigned int vm_page_purgeable_wired_count;/* How many purgeable pages are wired now ? */
extern
uint64_t vm_page_purged_count; /* How many pages got purged so far ? */
。它们在xnu-3789.51.2/osfmk/vm/vm_page.h中定义如下：
host_statistics64()关于我们只能使用/*
* vm_page_release:
*
* Return a page to the free list.
*/
void
vm_page_release(
vm_page_t mem,
boolean_t page_queues_locked)
{
[...]
vm_page_free_count++;
[...]
}
访问非常有限的数字的大量统计数据。这些统计数据中的大多数都在xnu-3789.51.2/osfmk/vm/vm_resident.c中更新。例如，此函数将页面释放到空闲页面列表：
extern unsigned int vm_page_stolen_count; /* Count of stolen pages not acccounted in zones */非常有趣的是* VM_PAGE_MAX_SPECULATIVE_AGE_Q * VM_PAGE_SPECULATIVE_Q_AGE_MS
* defines the amount of time a speculative page is normally
* allowed to live in the 'protected' state (i.e. not available
* to be stolen if vm_pageout_scan is running and looking for
* pages)... however, if the total number of speculative pages
* in the protected state exceeds our limit (defined in vm_pageout.c)
* and there are none available in VM_PAGE_SPECULATIVE_AGED_Q, then
* vm_pageout_scan is allowed to steal pages from the protected
* bucket even if they are underage.
*
* vm_pageout_scan is also allowed to pull pages from a protected
* bin if the bin has reached the "age of consent" we've set
。什么是被盗页面？似乎有一些机制可以从某些列表中删除页面，即使它通常不会被分页。其中一种机制是推测页面列表中页面的 age 。 xnu-3789.51.2/osfmk/vm/vm_page.h告诉我们
void vm_pageout_scan(void)确实vm_page_stolen_count增加host_statistics64()。您可以在xnu-3789.51.2/osfmk/vm/vm_pageout.c中找到相应的源代码。
我认为计算host_statistics64()的VM统计数据时不会考虑被盗页面。
证明我是对的
证明这一点的最佳方法是手动编译带有/usr/bin/top自定义版本的XNU。我没有机会这样做，但很快就会尝试。
幸运的是，我们并不是唯一对正确的VM统计信息感兴趣的人。因此，我们应该看看知识渊博的static int
libtop_tsamp_update_vm_stats(libtop_tsamp_t* tsamp) {
kern_return_t kr;
tsamp->p_vm_stat = tsamp->vm_stat;
mach_msg_type_number_t count = sizeof(tsamp->vm_stat) / sizeof(natural_t);
kr = host_statistics64(libtop_port, HOST_VM_INFO64, (host_info64_t)&tsamp->vm_stat, &count);
if (kr != KERN_SUCCESS) {
return kr;
}
if (tsamp->pages_stolen > 0) {
tsamp->vm_stat.wire_count += tsamp->pages_stolen;
}
[...]
return kr;
}
（未包含在XNU中）的实现，这里完全可用：top-108（我刚刚选择了macOS 10.12.4 release）。
让我们看一下top-108/libtop.c，我们会在其中找到以下内容：
tsamp libtop_tsamp_t属于vm_statistics64_data_t vm_stat类型，是top-108/libtop.h中定义的结构。它包含uint64_t pages_stolen和static int libtop_tsamp_update_vm_stats(libtop_tsamp_t* tsamp)等其他内容。
正如您所看到的，tsamp->vm_stat让host_statistics64()被tsamp->pages_stolen > 0填充，正如我们所知道的那样。之后，它会检查是否wire_count并将其添加到tsamp->vm_stat的{{1}}字段中。
2。结论如果我们只使用host_statistics64()中的/usr/bin/vm_stat或您的示例代码，我们就不会获得这些被盗网页的数量！
为什么host_statistics64()按原样实施？
老实说，我不知道。分页是一个复杂的过程，因此实时观察是一项具有挑战性的任务。我们必须注意到它的实现似乎没有错误。如果我们可以访问vm_page_stolen_count，我认为我们甚至无法获得100％准确的网页数。 /usr/bin/top的实施如果数量不是很大，则不会计算被盗网页的数量。
另一个有趣的事情是函数static void update_pages_stolen(libtop_tsamp_t *tsamp)上方的注释/* This is for <rdar://problem/6410098>. */。 Open Radar是Apple软件的错误报告网站，通常以评论中给出的格式对错误进行分类。我无法找到相关的bug;也许这是关于缺页。
我希望这些信息对您有所帮助。如果我设法在我的机器上编译最新（和定制）版本的XNU，我会告诉你。也许这会带来有趣的见解。
答案 1 :(得分：1)
注意到如果你将compressor_page_count添加到混音中，你会更接近机器中的实际RAM数量。
这是一个观察，而不是一个解释，并且链接到正确记录的位置会很好！