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

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Message-ID: <e5296d91-f734-fc2a-4b96-1fd2eebcbca5@redhat.com>
Date:   Thu, 6 Jul 2023 14:01:40 +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 13:59, Nanyong Sun wrote:
> 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.
> 

Again, already 1 year old. And returning garbage instead of ripping it 
out might be even nastier.

-- 
Cheers,

David / dhildenb