linux-kernel - Re: [PATCH linux-next v4] ksm: add ksm involvement information for each process

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Message-ID: <3a457ce5-3c5c-4165-996b-f5a46fcda194@redhat.com>
Date: Tue, 10 Dec 2024 21:05:18 +0100
From: David Hildenbrand <david@...hat.com>
To: Andrew Morton <akpm@...ux-foundation.org>, xu.xin16@....com.cn
Cc: linux-kernel@...r.kernel.org, wang.yaxin@....com.cn, linux-mm@...ck.org,
 linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH linux-next v4] ksm: add ksm involvement information for
 each process

On 04.12.24 01:56, Andrew Morton wrote:
> On Tue, 3 Dec 2024 19:26:33 +0800 (CST) <xu.xin16@....com.cn> wrote:
> 
>> From: xu xin <xu.xin16@....com.cn>
>>
>> In /proc/<pid>/ksm_stat, Add two extra ksm involvement items including
>> KSM_mergeable and KSM_merge_any. It helps administrators to
>> better know the system's KSM behavior at process level.
> 
> It's hard for me to judge the usefulness of this.  Please tell us more:
> usage examples, what actions have been taken using this information, etc.

Seconded.

> 
>> KSM_mergeable: yes/no
>> 	whether any VMAs of the process'mm are currently applicable to KSM.
> 
> Could we simply display VM_MERGEABLE in /proc/<pid>/maps?

We indicate in /proc/<pid>/smaps "mg" for VM_MERGEABLE already.

The "nasty" thing about smaps is that it does all the page table walking 
to gather memory statistics, which can be rather expensive.

I was recently asking myself whether we should have a "cheaper" way to 
obtain such details about mappings. /proc/<pid>/maps is likely 
impossible to extend (similarly display flags) I suspect.



-- 
Cheers,

David / dhildenb