linux-kernel - Re: [PATCH v9 3/5] ksm: add ksm zero pages for each process

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Date:   Wed, 24 May 2023 09:24:51 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Yang Yang <yang.yang29@....com.cn>, akpm@...ux-foundation.org
Cc:     imbrenda@...ux.ibm.com, jiang.xuexin@....com.cn,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        ran.xiaokai@....com.cn, xu.xin.sc@...il.com, xu.xin16@....com.cn
Subject: Re: [PATCH v9 3/5] ksm: add ksm zero pages for each process

On 24.05.23 07:58, Yang Yang wrote:
> From: xu xin <xu.xin16@....com.cn>
> 
> As the number of ksm zero pages is not included in ksm_merging_pages per
> process when enabling use_zero_pages, it's unclear of how many actual
> pages are merged by KSM. To let users accurately estimate their memory
> demands when unsharing KSM zero-pages, it's necessary to show KSM zero-
> pages per process. In addition, it help users to know the actual KSM
> profit because KSM-placed zero pages are also benefit from KSM.
> 
> since unsharing zero pages placed by KSM accurately is achieved, then
> tracking empty pages merging and unmerging is not a difficult thing any
> longer.
> 
> Since we already have /proc/<pid>/ksm_stat, just add the information of
> 'ksm_zero_pages' in it.
> 
> Signed-off-by: xu xin <xu.xin16@....com.cn>
> Cc: Claudio Imbrenda <imbrenda@...ux.ibm.com>
> Cc: David Hildenbrand <david@...hat.com>
> Cc: Xuexin Jiang <jiang.xuexin@....com.cn>
> Cc: Xiaokai Ran <ran.xiaokai@....com.cn>
> Cc: Yang Yang <yang.yang29@....com.cn>
> ---

[...]

>   static inline int ksm_fork(struct mm_struct *mm, struct mm_struct *oldmm)
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 306a3d1a0fa6..14f781509812 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -777,7 +777,7 @@ struct mm_struct {
>   #ifdef CONFIG_KSM
>   		/*
>   		 * Represent how many pages of this process are involved in KSM
> -		 * merging.
> +		 * merging (not including ksm_zero_pages).
>   		 */
>   		unsigned long ksm_merging_pages;
>   		/*
> @@ -785,7 +785,12 @@ struct mm_struct {
>   		 * including merged and not merged.
>   		 */
>   		unsigned long ksm_rmap_items;
> -#endif
> +		/*
> +		 * Represent how many empty pages are merged with kernel zero
> +		 * pages when enabling KSM use_zero_pages.

"zero page" ? Only some archs have multiple ones, and it's rather an 
implementation detail.

> +		 */
> +		unsigned long ksm_zero_pages;
> +#endif /* CONFIG_KSM */
>   #ifdef CONFIG_LRU_GEN
>   		struct {

Reviewed-by: David Hildenbrand <david@...hat.com>

-- 
Thanks,

David / dhildenb