linux-kernel - Re: [PATCH] mm/ksm: prepare to remove the redundant ksm_merging

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Date:   Thu, 6 Jul 2023 10:55:37 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Nanyong Sun <sunnanyong@...wei.com>, akpm@...ux-foundation.org
Cc:     xu.xin16@....com.cn, wangkefeng.wang@...wei.com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] mm/ksm: prepare to remove the redundant ksm_merging_pages
 in procfs

On 06.07.23 11:49, Nanyong Sun wrote:
> Since the ksm_merging_pages information already included in
> /proc/<pid>/ksm_stat, we could remove /proc/<pid>/ksm_merging_pages
> to make the directory more clean, and can save a little bit resources.
> 
> To delete this interface more smoothly and avoid userspace break,
> retain this interface temporarily and modify its function to hint
> users to use ksm_stat instead.
> 
> Signed-off-by: Nanyong Sun <sunnanyong@...wei.com>
> ---
>   fs/proc/base.c | 9 +--------
>   1 file changed, 1 insertion(+), 8 deletions(-)
> 
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index eb2e498e3b8d..d080c58cbe6c 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -3189,14 +3189,7 @@ static int proc_pid_patch_state(struct seq_file *m, struct pid_namespace *ns,
>   static int proc_pid_ksm_merging_pages(struct seq_file *m, struct pid_namespace *ns,
>   				struct pid *pid, struct task_struct *task)
>   {
> -	struct mm_struct *mm;
> -
> -	mm = get_task_mm(task);
> -	if (mm) {
> -		seq_printf(m, "%lu\n", mm->ksm_merging_pages);
> -		mmput(mm);
> -	}
> -
> +	seq_puts(m, "please use /proc/<pid>/ksm_stat instead\n");
>   	return 0;
>   }
>   static int proc_pid_ksm_stat(struct seq_file *m, struct pid_namespace *ns,


Why do we care so much about removing 15 simple LOC? That change here 
will already mess with user space.

Sorry, but IMHO it's all not worth the churn.

-- 
Cheers,

David / dhildenb