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

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Message-Id: <20190425150652.627fb21a40c18e1c32ed2125@linux-foundation.org>
Date:   Thu, 25 Apr 2019 15:06:52 -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-fsdevel@...r.kernel.org
Subject: Re: [PATCH] fs/proc: add VmTaskSize field to /proc/$$/status

On Thu, 25 Apr 2019 16:57:47 -0400 Joel Savitz <jsavitz@...hat.com> wrote:

> Currently, there is no fast mechanism to get the virtual memory size of
> the current process from userspace. This information is available to the
> user through several means, one being a linear search of the entire address
> space. This is the method used by a component of the libhugetlb kernel
> test, and using the mechanism proposed in this patch, the time complexity
> of that test would be upgraded to constant time from linear time. This is
> especially relevant on 64-bit architechtures where a linear search of
> the address space could take an absurd amount of time. Using this
> mechanism, the modification to the test component would be portable
> across all architechtures.

Please include all details on the observed performance improvements.

>  fs/proc/task_mmu.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)

Please update Documentation/filesystems/proc.txt.