From: Shakeel Butt <shakeelb@google.com>
To: Xishi Qiu <qiuxishi@huawei.com>
Cc: Linux MM <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org>
Subject: Re: [RFC] mm: why cat /proc/pid/smaps | grep Rss is different from cat /proc/pid/statm?
Date: Tue, 22 Mar 2016 07:47:29 -0700 [thread overview]
Message-ID: <CALvZod5PnHz5OsNrcfsMZ6=cxLBy9436htbKerv67S+CigwGbQ@mail.gmail.com> (raw)
In-Reply-To: <56F14EEE.7060308@huawei.com>
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On Tue, Mar 22, 2016 at 6:55 AM, Xishi Qiu <qiuxishi@huawei.com> 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
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next prev parent reply other threads:[~2016-03-22 14:47 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-22 13:55 [RFC] mm: why cat /proc/pid/smaps | grep Rss is different from cat /proc/pid/statm? Xishi Qiu
2016-03-22 14:47 ` Shakeel Butt [this message]
2016-03-30 7:16 ` Xishi Qiu
2016-03-30 9:39 ` Xishi Qiu
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