linux-kernel - Re: [PATCH v2] mm: ksm: Consider the number of ksm_mm_slot in the general

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Message-ID: <9e4bba64-c13f-4157-9258-c9b647ba9dd2@linux.dev>
Date: Fri, 21 Jun 2024 10:30:22 +0800
From: Chengming Zhou <chengming.zhou@...ux.dev>
To: David Hildenbrand <david@...hat.com>, Sung-hun Kim
 <sfoon.kim@...sung.com>, akpm@...ux-foundation.org, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org
Cc: sungguk.na@...sung.com, sw0312.kim@...sung.com, sebuns@...il.com
Subject: Re: [PATCH v2] mm: ksm: Consider the number of ksm_mm_slot in the
 general_profit calculation

On 2024/6/21 03:38, David Hildenbrand wrote:
> On 20.06.24 06:39, Sung-hun Kim wrote:
>> The current version of KSM does not take into account the number of
>> used ksm_mm_slot. Therefore, when users want to obtain profits of
>> KSM, KSM omits the memory used for allocating ksm_mm_slots.
>>
>> This patch introduces a new variable to keep track of the number of
>> allocated ksm_mm_slots. By doing so, KSM will be able to provide a
>> more accurate number of the gains made.
> 
> If you take a look at the calculation explained in 
> Documentation/admin-guide/mm/ksm.rst, we only care about rmap_items, 
> which can grow rather substantially in size.
> 
> We also don't consider other metadata, such as the size of the stable 
> nodes etc. So why should the ksm_mm_slots matter that much that we 
> should track them and account them?

BTW, the size of stable_nodes should be more than these mm_slots,
we have one stable_nodes for each KSM page now.

But agree, we only care about the rmap_items, which is the majority
of used memory resource in KSM.