linux-kernel - Re: [PATCH v5 1/3] mm, proc: Implement /proc/<pid>/totmaps

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Date:   Mon, 12 Sep 2016 18:12:28 -0400
From:   Robert Foss <robert.foss@...labora.com>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     corbet@....net, akpm@...ux-foundation.org, vbabka@...e.cz,
        hughd@...gle.com, mhocko@...e.com, koct9i@...il.com,
        n-horiguchi@...jp.nec.com, kirill.shutemov@...ux.intel.com,
        john.stultz@...aro.org, minchan@...nel.org,
        ross.zwisler@...ux.intel.com, jmarchan@...hat.com,
        hannes@...xchg.org, keescook@...omium.org, viro@...iv.linux.org.uk,
        mguzik@...hat.com, jdanis@...gle.com, calvinowens@...com,
        adobriyan@...il.com, ebiederm@...ssion.com, sonnyrao@...omium.org,
        seth.forshee@...onical.com, tixxdz@...il.com,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        Ben Zhang <benzh@...omium.org>,
        Bryan Freed <bfreed@...omium.org>,
        Filipe Brandenburger <filbranden@...omium.org>,
        Jann Horn <jann@...jh.net>, Michal Hocko <mhocko@...nel.org>,
        linux-api@...r.kernel.org,
        Jacek Anaszewski <j.anaszewski@...sung.com>
Subject: Re: [PATCH v5 1/3] mm, proc: Implement /proc/<pid>/totmaps

Hey Oleg!

Thanks for the feedback, I'll keep it in mind, but currently it looks 
like the patch is on ice for non-implementation related reasons.


Rob.

>>
>> @@ -2854,6 +2854,7 @@ static const struct pid_entry tgid_base_stuff[] = {
>>  	REG("clear_refs", S_IWUSR, proc_clear_refs_operations),
>>  	REG("smaps",      S_IRUGO, proc_pid_smaps_operations),
>>  	REG("pagemap",    S_IRUSR, proc_pagemap_operations),
>> +	REG("totmaps",    S_IRUGO, proc_totmaps_operations),
>
> I must have missed something, but I fail to understand why this patch
> is so complicated.
>
> Just use ONE("totmaps", S_IRUGO, proc_totmaps_operations) ?
>
>> +static int totmaps_proc_show(struct seq_file *m, void *data)
>> +{
>> +	struct proc_maps_private *priv = m->private;
>> +	struct mm_struct *mm = priv->mm;
>> +	struct vm_area_struct *vma;
>> +	struct mem_size_stats mss_sum;
>> +
>> +	memset(&mss_sum, 0, sizeof(mss_sum));
>> +	down_read(&mm->mmap_sem);
>> +	hold_task_mempolicy(priv);
>         ^^^^^^^^^^^^^^^^^^^^^^^^^
> why?
>
>> +	for (vma = mm->mmap; vma != priv->tail_vma; vma = vma->vm_next) {
>
> Hmm. the usage of ->tail_vma looks just wrong. I guess the code should
> work because it is NULL but still.
>
>> +		struct mem_size_stats mss;
>> +		struct mm_walk smaps_walk = {
>> +			.pmd_entry = smaps_pte_range,
>> +			.mm = vma->vm_mm,
>> +			.private = &mss,
>> +		};
>> +
>> +		if (vma->vm_mm && !is_vm_hugetlb_page(vma)) {
>> +			memset(&mss, 0, sizeof(mss));
>> +			walk_page_vma(vma, &smaps_walk);
>> +			add_smaps_sum(&mss, &mss_sum);
>> +		}
>> +	}
>
> Why? I mean, why not walk_page_range() ? You do not need this for-each-vma
> loop at all? At least if you change this patch to use the ONE() helper, and
> everything else looks unneeded in this case.
>
> Oleg.
>