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

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Message-ID: <848fb72a-60a3-bf1d-a091-c25090175eb7@huawei.com>
Date:   Thu, 6 Jul 2023 19:59:50 +0800
From:   Nanyong Sun <sunnanyong@...wei.com>
To:     David Hildenbrand <david@...hat.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 2023/7/6 16:55, David Hildenbrand wrote:

> 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.
>
We do not pay attention to these 15 LOC. We pay more attention to the 
redundant interface under procfs.

This interface is used by developers and has a short history. Therefore, 
changing it now has no big impact.