linux-kernel - Re: [PATCH v5 4/6] ksm: count zero pages for each process

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Date:   Wed, 18 Jan 2023 15:31:16 +0100
From:   David Hildenbrand <david@...hat.com>
To:     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 v5 4/6] ksm: count zero pages for each process

On 30.12.22 02:16, yang.yang29@....com.cn 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.
> 
> 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
> zero_pages_sharing in it.
> 
> 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>
> Signed-off-by: xu xin <xu.xin16@....com.cn>
> ---
>   fs/proc/base.c           | 1 +
>   include/linux/mm_types.h | 7 ++++++-
>   mm/ksm.c                 | 2 ++
>   3 files changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index 9e479d7d202b..ac9ebe972be0 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -3207,6 +3207,7 @@ static int proc_pid_ksm_stat(struct seq_file *m, struct pid_namespace *ns,
>   	mm = get_task_mm(task);
>   	if (mm) {
>   		seq_printf(m, "ksm_rmap_items %lu\n", mm->ksm_rmap_items);
> +		seq_printf(m, "zero_pages_sharing %lu\n", mm->ksm_zero_pages_sharing);
>   		mmput(mm);
>   	}
> 
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 4e1031626403..5c734ebc1890 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -776,7 +776,7 @@ struct mm_struct {
>   #ifdef CONFIG_KSM
>   		/*
>   		 * Represent how many pages of this process are involved in KSM
> -		 * merging.
> +		 * merging (not including ksm_zero_pages_sharing).
>   		 */
>   		unsigned long ksm_merging_pages;
>   		/*
> @@ -784,6 +784,11 @@ struct mm_struct {
>   		 * including merged and not merged.
>   		 */
>   		unsigned long ksm_rmap_items;
> +		/*
> +		 * Represent how many empty pages are merged with kernel zero
> +		 * pages when enabling KSM use_zero_pages.
> +		 */
> +		unsigned long ksm_zero_pages_sharing;

Same comment as for previous patch: this counts rmap itmaps, no? 
ksm_zero_rmap_items might be more appropriate.

-- 
Thanks,

David / dhildenb