/proc/meminfo文件分析

最新推荐文章于 2025-05-03 19:30:00 发布

最新推荐文章于 2025-05-03 19:30:00 发布 · 302 阅读

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#数据结构与算法 #运维 #awk

本文详细解析了/proc/meminfo中各项内存指标的含义，包括MemTotal、MemFree、Buffers、Cached等，并介绍了这些指标如何帮助理解系统的内存使用情况。

from : http://blog.youkuaiyun.com/liujishen/article/details/4979503

The entries in the /proc/meminfo can help explain what's going on with your memory usage, if you know how to read it.

Example of "cat /proc/meminfo":

root:    total:        used:        free:          shared:    buffers:    cached:
Mem:      1055760384    1041887232    13873152    0    100417536     711233536
Swap:     1077501952      8540160     1068961792

MemTotal:        1031016 kB    
MemFree:        13548 kB
MemShared:        0 kB
Buffers:        98064 kB
Cached:            692320 kB
SwapCached:        2244 kB
Active:            563112 kB
Inact_dirty:        309584 kB
Inact_clean:        79508 kB
Inact_target:        190440 kB
HighTotal:        130992 kB
HighFree:        1876 kB
LowTotal:        900024 kB
LowFree:        11672 kB
SwapTotal:        1052248 kB
SwapFree:        1043908 kB
Committed_AS:        332340 kB

The information comes in the form of both high-level and low-level statistics. At the top you see a quick summary of the most common values people would like to look at. Below you find the individual values we will discuss. First we will discuss the high-level statistics.

High-Level Statistics

MemTotal: Total usable ram (i.e. physical ram minus a few reserved bits and the kernel binary code)
MemFree: Is sum of LowFree+HighFree (overall stat)
MemShared: 0; is here for compat reasons but always zero.
Buffers: Memory in buffer cache. mostly useless as metric nowadays
Cached: Memory in the pagecache (diskcache) minus SwapCache
SwapCache: Memory that once was swapped out, is swapped back in but still also is in the swapfile (if memory is needed it doesn't need to be swapped out AGAIN because it is already in the swapfile. This saves I/O)

Detailed Level Statistics
VM Statistics

VM splits the cache pages into "active" and "inactive" memory. The idea is that if you need memory and some cache needs to be sacrificed for that, you take it from inactive since that's expected to be not used. The vm checks what is used on a regular basis and moves stuff around.

When you use memory, the CPU sets a bit in the pagetable and the VM checks that bit occasionally, and based on that, it can move pages back to active. And within active there's an order of "longest ago not used" (roughly, it's a little more complex in reality). The longest-ago used ones can get moved to inactive. Inactive is split into two in the above kernel (2.4.18-24.8.0). Some have it three.

Active: Memory that has been used more recently and usually not reclaimed unless absolutely necessary.
Inact_dirty: Dirty means "might need writing to disk or swap." Takes more work to free. Examples might be files that have not been written to yet. They aren't written to memory too soon in order to keep the I/O down. For instance, if you're writing logs, it might be better to wait until you have a complete log ready before sending it to disk.
Inact_clean: Assumed to be easily freeable. The kernel will try to keep some clean stuff around always to have a bit of breathing room.
Inact_target: Just a goal metric the kernel uses for making sure there are enough inactive pages around. When exceeded, the kernel will not do work to move pages from active to inactive. A page can also get inactive in a few other ways, e.g. if you do a long sequential I/O, the kernel assumes you're not going to use that memory and makes it inactive preventively. So you can get more inactive pages than the target because the kernel marks some cache as "more likely to be never used" and lets it cheat in the "last used" order.

Memory Statistics

HighTotal: is the total amount of memory in the high region. Highmem is all memory above (approx) 860MB of physical RAM. Kernel uses indirect tricks to access the high memory region. Data cache can go in this memory region.
LowTotal: The total amount of non-highmem memory.
LowFree: The amount of free memory of the low memory region. This is the memory the kernel can address directly. All kernel datastructures need to go into low memory.
SwapTotal: Total amount of physical swap memory.
SwapFree: Total amount of swap memory free.
Committed_AS: An estimate of how much RAM you would need to make a 99.99% guarantee that there never is OOM (out of memory) for this workload. Normally the kernel will overcommit memory. That means, say you do a 1GB malloc, nothing happens, really. Only when you start USING that malloc memory you will get real memory on demand, and just as much as you use. So you sort of take a mortgage and hope the bank doesn't go bust. Other cases might include when you mmap a file that's shared only when you write to it and you get a private copy of that data. While it normally is shared between processes. The Committed_AS is a guesstimate of how much RAM/swap you would need worst-case.

> cat /proc/meminfo 读出的内核信息进行解释，

下篇文章会简单对读出该信息的代码进行简单的分析。

MemTotal: 507480 kB
MemFree: 10800 kB
Buffers: 34728 kB
Cached: 98852 kB
SwapCached: 128 kB
Active: 304248 kB
Inactive: 46192 kB
HighTotal: 0 kB
HighFree: 0 kB
LowTotal: 507480 kB
LowFree: 10800 kB
SwapTotal: 979956 kB
SwapFree: 941296 kB
Dirty: 32 kB
Writeback: 0 kB
AnonPages: 216756 kB
Mapped: 77560 kB
Slab: 22952 kB
SReclaimable: 15512 kB
SUnreclaim: 7440 kB
PageTables: 2640 kB
NFS_Unstable: 0 kB
Bounce: 0 kB
CommitLimit: 1233696 kB
Committed_AS: 828508 kB
VmallocTotal: 516088 kB
VmallocUsed: 5032 kB
VmallocChunk: 510580 kB

相应选项中文意思想各位高手已经知道，如何翻译有什么错误，请务必指出：

MemTotal: 所有可用RAM大小（即物理内存减去一些预留位和内核的二进制代码大小）

MemFree: LowFree与HighFree的总和，被系统留着未使用的内存

Buffers: 用来给文件做缓冲大小

Cached: 被高速缓冲存储器（cache memory）用的内存的大小（等于 diskcacheminusSwapCache ）.

SwapCached:被高速缓冲存储器（cache memory）用的交换空间的大小
已经被交换出来的内存，但仍然被存放在swapfile中。用来在需要的时候很快的被替换而不需要再次打开I/O端口。

Active: 在活跃使用中的缓冲或高速缓冲存储器页面文件的大小，除非非常必要否则不会被移作他用.

Inactive: 在不经常使用中的缓冲或高速缓冲存储器页面文件的大小，可能被用于其他途径.

HighTotal:
HighFree: 该区域不是直接映射到内核空间。内核必须使用不同的手法使用该段内存。

LowTotal:
LowFree: 低位可以达到高位内存一样的作用，而且它还能够被内核用来记录一些自己的数据结构。Among many
other things, it is where everything from the Slab is
allocated. Bad things happen when you're out of lowmem.

SwapTotal: 交换空间的总大小

SwapFree: 未被使用交换空间的大小

Dirty: 等待被写回到磁盘的内存大小。

Writeback: 正在被写回到磁盘的内存大小。

AnonPages：未映射页的内存大小

Mapped: 设备和文件等映射的大小。

Slab: 内核数据结构缓存的大小，可以减少申请和释放内存带来的消耗。

SReclaimable:可收回Slab的大小

SUnreclaim：不可收回Slab的大小（SUnreclaim+SReclaimable＝Slab）

PageTables：管理内存分页页面的索引表的大小。

NFS_Unstable:不稳定页表的大小

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虚拟内存大小

VmallocUsed: 已经被使用的虚拟内存大小。

VmallocChunk: largest contigious block of vmalloc area which is free

下面简单来个例子，看看已用内存和物理内存大小..

#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;
}

结果：Used 488M/Total 495M