From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1752879AbbANWlI (ORCPT <rfc822;w@1wt.eu>);
	Wed, 14 Jan 2015 17:41:08 -0500
Received: from mta-out1.inet.fi ([62.71.2.203]:58566 "EHLO jenni2.inet.fi"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1752493AbbANWlF (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
	Wed, 14 Jan 2015 17:41:05 -0500
Date: Thu, 15 Jan 2015 00:40:46 +0200
From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Calvin Owens <calvinowens@fb.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
        Alexey Dobriyan <adobriyan@gmail.com>, Oleg Nesterov <oleg@redhat.com>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Peter Feiner <pfeiner@google.com>,
        Grant Likely <grant.likely@secretlab.ca>,
        Siddhesh Poyarekar <siddhesh.poyarekar@gmail.com>,
        linux-kernel@vger.kernel.org, kernel-team@fb.com
Subject: Re: [RFC][PATCH] procfs: Add /proc/<pid>/mapped_files
Message-ID: <20150114224046.GA14340@node.dhcp.inet.fi>
References: <1421194829-28696-1-git-send-email-calvinowens@fb.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <1421194829-28696-1-git-send-email-calvinowens@fb.com>
User-Agent: Mutt/1.5.23.1 (2014-03-12)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Tue, Jan 13, 2015 at 04:20:29PM -0800, Calvin Owens wrote:
> Commit b76437579d1344b6 ("procfs: mark thread stack correctly in
> proc/<pid>/maps") introduced logic to mark thread stacks with the
> "[stack:%d]" marker in /proc/<pid>/maps.
> 
> This causes reading /proc/<pid>/maps to take O(N^2) time, where N is
> the number of threads sharing an address space, since each line of
> output requires iterating over the VMA list looking for ranges that
> correspond to the stack pointer in any task's register set. When
> dealing with highly-threaded Java applications, reading this file can
> take hours and trigger softlockup dumps.
> 
> Eliminating the "[stack:%d]" marker is not a viable option since it's
> been there for some time, and I don't see a way to do the stack check
> more efficiently that wouldn't end up making the whole thing really
> ugly.

Can we find stack for threads once on seq_operations::start() and avoid
for_each_thread() on seq_operations::show() for each stack vma?

-- 
 Kirill A. Shutemov