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

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Message-ID: <20160907125806.GA3849@redhat.com>
Date:   Wed, 7 Sep 2016 14:58:07 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     robert.foss@...labora.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

On 09/05, robert.foss@...labora.com wrote:
>
> @@ -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.