Re: [RFC] mm: why cat /proc/pid/smaps | grep Rss is different from cat /proc/pid/statm?

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From: Xishi Qiu <qiuxishi@huawei.com>
To: Shakeel Butt <shakeelb@google.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: Wed, 30 Mar 2016 17:39:47 +0800	[thread overview]
Message-ID: <56FB9EE3.7010208@huawei.com> (raw)
In-Reply-To: <56FB7D37.5070503@huawei.com>

On 2016/3/30 15:16, Xishi Qiu wrote:

> On 2016/3/22 22:47, Shakeel Butt wrote:
> 
>>
>> On Tue, Mar 22, 2016 at 6:55 AM, Xishi Qiu <qiuxishi@huawei.com <mailto: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
> 

Hi Shakeel,

I misunderstand your meaning before. I know the reason now.

Thanks,
Xishi Qiu 

> Hi Shakeel,
> 
> I malloc and memset 10M, then sleep. It seems that the problem is still exist,
> the kernel version is v4.1
>


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WARNING: multiple messages have this Message-ID (diff)

From: Xishi Qiu <qiuxishi@huawei.com>
To: Shakeel Butt <shakeelb@google.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: Wed, 30 Mar 2016 17:39:47 +0800	[thread overview]
Message-ID: <56FB9EE3.7010208@huawei.com> (raw)
In-Reply-To: <56FB7D37.5070503@huawei.com>

On 2016/3/30 15:16, Xishi Qiu wrote:

> On 2016/3/22 22:47, Shakeel Butt wrote:
> 
>>
>> On Tue, Mar 22, 2016 at 6:55 AM, Xishi Qiu <qiuxishi@huawei.com <mailto: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
> 

Hi Shakeel,

I misunderstand your meaning before. I know the reason now.

Thanks,
Xishi Qiu 

> Hi Shakeel,
> 
> I malloc and memset 10M, then sleep. It seems that the problem is still exist,
> the kernel version is v4.1
>

next prev parent reply	other threads:[~2016-03-30  9:44 UTC|newest]

Thread overview: 7+ 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 13:55 ` Xishi Qiu
2016-03-22 14:47 ` Shakeel Butt
2016-03-30  7:16   ` Xishi Qiu
2016-03-30  7:16     ` Xishi Qiu
2016-03-30  9:39     ` Xishi Qiu [this message]
2016-03-30  9:39       ` Xishi Qiu

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