linux-kernel - Re: [PATCH v6 4/6] ksm: count zero pages for each process

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Date:   Tue, 7 Mar 2023 19:45:57 +0100
From:   Claudio Imbrenda <imbrenda@...ux.ibm.com>
To:     <yang.yang29@....com.cn>
Cc:     <akpm@...ux-foundation.org>, <david@...hat.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 v6 4/6] ksm: count zero pages for each process

On Fri, 10 Feb 2023 09:19:49 +0800 (CST)
<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>

Reviewed-by: Claudio Imbrenda <imbrenda@...ux.ibm.com>

> ---
>  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;
>  #endif
>  #ifdef CONFIG_LRU_GEN
>  		struct {
> diff --git a/mm/ksm.c b/mm/ksm.c
> index 1fa668e1fe82..42dbcc3ec90d 100644
> --- a/mm/ksm.c
> +++ b/mm/ksm.c
> @@ -794,6 +794,7 @@ static inline void clean_rmap_item_zero_flag(struct ksm_rmap_item *rmap_item)
>  {
>  	if (rmap_item->address & ZERO_PAGE_FLAG) {
>  		ksm_zero_pages_sharing--;
> +		rmap_item->mm->ksm_zero_pages_sharing--;
>  		rmap_item->address &= PAGE_MASK;
>  	}
>  }
> @@ -2117,6 +2118,7 @@ static int try_to_merge_with_kernel_zero_page(struct ksm_rmap_item *rmap_item,
>  			if (!err) {
>  				rmap_item->address |= ZERO_PAGE_FLAG;
>  				ksm_zero_pages_sharing++;
> +				rmap_item->mm->ksm_zero_pages_sharing++;
>  			}
>  		} else {
>  			/* If the vma is out of date, we do not need to continue. */