linux /proc/meminfo文件分析 .

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。
# cat /proc/meminfo
MemTotal:     16438852 kB
MemFree:      10980184 kB
Buffers:         95884 kB
Cached:         224108 kB
SwapCached:          0 kB
Active:        5161616 kB
Inactive:       217660 kB
HighTotal:           0 kB
HighFree:            0 kB
LowTotal:     16438852 kB
LowFree:      10980184 kB
SwapTotal:     1048536 kB
SwapFree:      1048536 kB
Dirty:             424 kB
Writeback:           0 kB
AnonPages:     5059312 kB
Mapped:          20424 kB
Slab:            38176 kB
PageTables:      13480 kB
NFS_Unstable:        0 kB
Bounce:              0 kB
CommitLimit:   9267960 kB
Committed_AS: 10073960 kB
VmallocTotal: 34359738367 kB
VmallocUsed:    263672 kB
VmallocChunk: 34359473751 kB
HugePages_Total:     0
HugePages_Free:      0
HugePages_Rsvd:      0
Hugepagesize:     2048 kB

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 diskcache minus SwapCache ）. 

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

备注：

占用内存的测量

测量一个进程占用了多少内存，linux为我们提供了一个很方便的方法，/proc目录为我们提供了所有的信息，实际上top等工具也通过这里来获取相应的信息。

/proc/meminfo 机器的内存使用信息

/proc/pid/maps pid为进程号，显示当前进程所占用的虚拟地址。

/proc/pid/statm 进程所占用的内存

/proc/pid/status  提供更容易理解stat和statm的信息

# cat /proc/pid/statm

654 57 44 0 0 334 0

输出解释
man 5 proc, 搜statm。从左到右依次内容为:

size 程序大小
resident 常驻内存空间大小
share 共享内存页数
text 代码段占用内存页数
lib 引用库占用内存页数
data 数据/堆栈段占用内存页数
dt 脏页数量

# cat /proc/pid/status

Size (pages) 任务虚拟地址空间的大小 VmSize/4

Resident(pages) 应用程序正在使用的物理内存的大小 VmRSS/4

Shared(pages) 共享页数 0

Trs(pages) 程序所拥有的可执行虚拟内存的大小 VmExe/4

Lrs(pages) 被映像到任务的虚拟内存空间的库的大小 VmLib/4

Drs(pages) 程序数据段和用户态的栈的大小 （VmData+ VmStk ）4

dt(pages) 04