linux-kernel - Re: [PATCH v4] fs/proc: add VmTaskSize field to /proc/$$/status

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Message-Id: <20190613122956.2fe1e200419c6497159044a0@linux-foundation.org>
Date:   Thu, 13 Jun 2019 12:29:56 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Joel Savitz <jsavitz@...hat.com>
Cc:     linux-kernel@...r.kernel.org,
        Alexey Dobriyan <adobriyan@...il.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Ram Pai <linuxram@...ibm.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Huang Ying <ying.huang@...el.com>,
        Sandeep Patil <sspatil@...roid.com>,
        Rafael Aquini <aquini@...hat.com>, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v4] fs/proc: add VmTaskSize field to /proc/$$/status

On Thu, 13 Jun 2019 10:54:50 -0400 Joel Savitz <jsavitz@...hat.com> wrote:

> The kernel provides no architecture-independent mechanism to get the
> size of the virtual address space of a task (userspace process) without
> brute-force calculation. This patch allows a user to easily retrieve
> this value via a new VmTaskSize entry in /proc/$$/status.

Why is access to ->task_size required?  Please fully describe the
use case.

> --- a/Documentation/filesystems/proc.txt
> +++ b/Documentation/filesystems/proc.txt
> @@ -187,6 +187,7 @@ read the file /proc/PID/status:
>    VmLib:      1412 kB
>    VmPTE:        20 kb
>    VmSwap:        0 kB
> +  VmTaskSize:	137438953468 kB
>    HugetlbPages:          0 kB
>    CoreDumping:    0
>    THP_enabled:	  1
> @@ -263,6 +264,7 @@ Table 1-2: Contents of the status files (as of 4.19)
>   VmPTE                       size of page table entries
>   VmSwap                      amount of swap used by anonymous private data
>                               (shmem swap usage is not included)
> + VmTaskSize                  size of task (userspace process) vm space

This is rather vague.  Is it the total amount of physical memory?  The
sum of all vma sizes, populated or otherwise?  Something else?