主要參考內核文檔和紅帽文檔對
> cat /proc/meminfo 讀出的內核信息進行解釋，
下篇文章會簡單對讀出該信息的代碼進行簡單的分析。
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相應選項中文意思想各位高手已經知道，如果翻譯有什麼錯誤，請務必指出：
MemTotal: 所有可用RAM大小 （即物理內存減去一些預留位和內核的二進制代碼大小）
MemFree: LowFree與HighFree的總和，被系統留着未使用的內存
Buffers: 用來給文件做緩衝大小
Cached: 被高速緩衝存儲器（cache memory）用的內存的大小（等於 diskcache minus SwapCache ）.
SwapCached:被高速緩衝存儲器（cache memory）用的交換空間的大小已經
被交換出來的內存，但仍然被存放在swapfile中。用來在需要的時候很快的
被替換而不需要再次打開I/O端口。
Active: 在活躍使用中的緩衝或高速緩衝存儲器頁面文件的大小，除非非常必要否則不會被移作他用.
Inactive: 在不經常使用中的緩衝或高速緩衝存儲器頁面文件的大小，可能被用於其他途徑.
HighTotal:
HighFree: 該區域不是直接映射到內核空間。內核必須使用不同的手法使用該段內存。
LowTotal:
LowFree: 低位可以達到高位內存一樣的作用，而且它還能夠被內核用來記錄
一些自己的數據結構。Among many other things, it is where
everything from the Slab is allocated. Bad things happen
when you’re out of lowmem.
SwapTotal: 交換空間的總大小
SwapFree: 未被使用交換空間的大小
Dirty: 等待被寫回到磁盤的內存大小。
Writeback: 正在被寫回到磁盤的內存大小。
AnonPages：未映射頁的內存大小
Mapped: 設備和文件等映射的大小。
Slab: 內核數據結構緩存的大小，可以減少申請和釋放內存帶來的消耗。
SReclaimable:可收回Slab的大小
SUnreclaim：不可收回Slab的大小（SUnreclaim+SReclaimable＝Slab）
PageTables：管理內存分頁頁面的索引表的大小。
NFS_Unstable:不穩定頁表的大小
Bounce:
CommitLimit: Based on the overcommit ratio(‘vm.overcommit_ratio’),
this is the total amount of memory currently available to
be allocated on the system. This limit is only adhered to
if strict overcommit accounting is enabled (mode 2 in
‘vm.overcommit_memory’).
The CommitLimit is calculated with the following formula:
CommitLimit = (‘vm.overcommit_ratio’ * Physical RAM) + Swap
For example, on a system with 1G of physical RAM and 7G
of swap with a `vm.overcommit_ratio` of 30 it would
yield a CommitLimit of 7.3G.
For more details, see the memory overcommit documentation
in vm/overcommit-accounting.
Committed_AS: The amount of memory presently allocated on
the system.
The committed memory is a sum of all of the memory which
has been allocated by processes, even if it has not been
“used” by them as of yet. A process which malloc()’s 1G
of memory, but only touches 300M of it will only show up
as using 300M of memory even if it has the address space
allocated for the entire 1G. This 1G is memory which has
been “committed” to by the VM and can be used at any time
by the allocating application. With strict overcommit
enabled on the system (mode 2 in ‘vm.overcommit_memory’),
allocations which would exceed the CommitLimit (detailed
above) will not be permitted. This is useful if one needs
to guarantee that processes will not fail due to lack of
memory once that memory has been successfully allocated.
VmallocTotal: 可以vmalloc虛擬內存大小
VmallocUsed: 已經被使用的虛擬內存大小。
VmallocChunk: largest contigious block of vmalloc area which is free
下面簡單來個例子，看看已用內存和物理內存大小..
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int MemInfo(char* Info, int len);
int main()
{
char buf[128];
memset(buf, 0, 128);
MemInfo(buf, 100);
printf("%s", buf);
return 0;
}
int MemInfo(char* Info, int len)
{
char sStatBuf[256];
FILE* fp;
int flag;
int TotalMem;
int UsedMem;
char* line;
if(system("free -m | awk '{print $2,$3}' > mem"));
memset(sStatBuf, 0, 256);
fp = fopen("mem", "rb");
if(fp < 0)
{
return -1;
}
fread(sStatBuf,1, sizeof(sStatBuf) , fp);
line = strstr(sStatBuf, “\n”);
TotalMem = atoi(line);
line = strstr(line, ” “);
UsedMem = atoi(line);
memset(sStatBuf, 0, 256);
sprintf(sStatBuf, “Used %dM/Total %dM\n”, UsedMem, TotalMem);
if(strlen(sStatBuf) > len)
{
return -1;
}
memcpy(Info, sStatBuf, strlen(sStatBuf));
return 0;
}
結果：Used 488M/Total 495M
上面文章對meminfo裏的信息做出簡單的解釋了
那麼內核怎麼把meminfo信息動態反應到meminfo文件中呢
在內核 linux/fs/proc/proc_misc.c中
#define K(x) ((x) << (PAGE_SHIFT - 10)) /** get_vmalloc_info(&vmi); return proc_calc_metrics(page, start, off, count, eof, len); |
其中sysinfo結構在 linux/kernel.h 定義：
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而global_page_state()函數中的常量定義在 linux/mmzone.h
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其中通過global_page_state()函數根據 zone_stat_item 結構的常量得到不同區大小，會跟 vm_stat[NR_VM_ZONE_STAT_ITEMS]對應起來。
vm_stat[]是統計各區的大小。
內核 linux/vmstat.h定義：static inline unsigned long global_page_state(enum zone_stat_item item)
{
long x = atomic_long_read(&vm_stat[item]);
#ifdef CONFIG_SMP
if (x < 0)
x = 0;
#endif
return x;
}
下面根據struct sysinfo結構，簡單分析CPU和內存使用信息。
#include <stdio.h>
#include <linux/unistd.h> /* 包含調用 _syscallX 宏等相關信息*/
#include <linux/kernel.h> /* 包含sysinfo結構體信息*/
int main(int argc, char *agrv[])
{
struct sysinfo s_info;
int error;
error = sysinfo(&s_info);
printf(“\n\ncode error=%d\n”,error);
printf(“Uptime = %ds\nLoad: 1 min%d / 5 min %d / 15 min %d\n”
“RAM: total %d / free %d /shared%d\n”
“Memory in buffers = %d\nSwap:total%d/free%d\n”
“Number of processes = %d\n”,
s_info.uptime, s_info.loads[0],
s_info.loads[1], s_info.loads[2],
s_info.totalram, s_info.freeram,
s_info.totalswap, s_info.freeswap,
s_info.procs);
return 0;
}
結果：
code error=0
Uptime = 8329s
Load: 1 min37152 / 5 min 37792 / 15 min 48672
RAM: total 519659520 / free 9031680 /shared1003474944
Memory in buffers = 937451520
Swap:total223/free-1078732672
Number of processes = -1078732608