On Tue, Mar 22, 2016 at 6:55 AM, Xishi Qiu [off-list ref] wrote:

[root@localhost c_test]# cat /proc/3948/smaps | grep Rss

The /proc/[pid]/smaps read triggers the traversal of all of process's vmas
and then page tables and accumulate RSS on each present page table entry.

[root@localhost c_test]# cat /proc/3948/statm

1042 173 154 1 0 48 0

The files /proc/[pid]/statm and /proc/[pid]/status uses the counters
(MM_ANONPAGES & MM_FILEPAGES) in mm_struct to report RSS of a process.
These counters are modified on page table modifications. However the kernel
implements an optimization where each thread keeps a local copy of these
counters in its task_struct. These local counter are accumulated in the
shared counter of mm_struct after some number of page faults (I think 32)
faced by the thread and thus there will be mismatch with smaps file.

Shakeel