linux -/proc/pid/smaps中的pss是什么意思

Question

我对/proc/pid/smaps中的Pss列感到困惑，所以我写了一个程序来测试它:

void sa();
int main(int argc,char *argv[])
{
    int fd;
    sa();
    sleep(1000);
}

void sa()
{
   char *pi=new char[1024*1024*10];
   for(int i=0;i<4;++i) {
        for(int j=0;j<1024*1024;++j){
                *pi='o';
                pi++;
        }
   }
   int cnt;
   for(int i=0;i<6;++i) {
        for(int j=0;j<1024*1024;++j){
                cnt+=*pi;
                pi++;
        }
   }
   printf("%d",cnt);
}

$cat /proc/`pidof testprogram`/smaps

08838000-0885b000 rw-p 00000000 00:00 0          [heap]
Size:                140 kB
Rss:                  12 kB
Pss:                  12 kB
Shared_Clean:          0 kB
Shared_Dirty:          0 kB
Private_Clean:         0 kB
Private_Dirty:        12 kB
Referenced:           12 kB
Swap:                  0 kB
KernelPageSize:        4 kB
MMUPageSize:           4 kB
b6dcd000-b77d0000 rw-p 00000000 00:00 0 
Size:              10252 kB
Rss:               10252 kB
Pss:                4108 kB
Shared_Clean:          0 kB
Shared_Dirty:          0 kB
Private_Clean:         0 kB
Private_Dirty:      4108 kB
Referenced:         4108 kB
Swap:                  0 kB
KernelPageSize:        4 kB
MMUPageSize:           4 kB

在这里我发现 Pss 等于 Private_Dirty，但我想知道为什么。

顺便说一句:smaps 有详细的文档吗？

Answer 1

引自lwn.net

The "proportional set size" (PSS) of a process is the count of pages it has in memory, where each page is divided by the number of processes sharing it. So if a process has 1000 pages all to itself, and 1000 shared with one other process, its PSS will be 1500

来自 Linux Kernel Documentation ,

/proc/PID/smaps是基于 map 的扩展，显示内存 每个进程映射的消耗。对于那里的每个映射 是一系列的行，如下所示:

08048000-080bc000 r-xp 00000000 03:02 13130      /bin/bash
Size:               1084 kB
Rss:                 892 kB
Pss:                 374 kB
Shared_Clean:        892 kB
Shared_Dirty:          0 kB
Private_Clean:         0 kB
Private_Dirty:         0 kB
Referenced:          892 kB
Anonymous:             0 kB
Swap:                  0 kB
KernelPageSize:        4 kB
MMUPageSize:           4 kB
Locked:              374 kB

The first of these lines shows the same information as is displayed for the mapping in /proc/PID/maps. The remaining lines show the size of the mapping (size), the amount of the mapping that is currently resident in RAM (RSS), the process' proportional share of this mapping (PSS), the number of clean and dirty private pages in the mapping. Note that even a page which is part of a MAP_SHARED mapping, but has only a single pte mapped, i.e. is currently used by only one process, is accounted as private and not as shared. "Referenced" indicates the amount of memory currently marked as referenced or accessed. "Anonymous" shows the amount of memory that does not belong to any file. Even a mapping associated with a file may contain anonymous pages: when MAP_PRIVATE and a page is modified, the file page is replaced by a private anonymous copy. "Swap" shows how much would-be-anonymous memory is also used, but out on swap.

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