From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933285AbcASWOl (ORCPT ); Tue, 19 Jan 2016 17:14:41 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:51425 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932252AbcASWOe (ORCPT ); Tue, 19 Jan 2016 17:14:34 -0500 Date: Tue, 19 Jan 2016 14:14:30 -0800 From: Andrew Morton To: Johannes Weiner Cc: Shaohua Li , Siddhesh Poyarekar , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@fb.com Subject: Re: [PATCH] proc: revert /proc//maps [stack:TID] annotation Message-Id: <20160119141430.8ff9c464.akpm@linux-foundation.org> In-Reply-To: <1453226559-17322-1-git-send-email-hannes@cmpxchg.org> References: <1453226559-17322-1-git-send-email-hannes@cmpxchg.org> X-Mailer: Sylpheed 2.7.1 (GTK+ 2.18.9; x86_64-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 19 Jan 2016 13:02:39 -0500 Johannes Weiner wrote: > b764375 ("procfs: mark thread stack correctly in proc//maps") > added [stack:TID] annotation to /proc//maps. Finding the task of > a stack VMA requires walking the entire thread list, turning this into > quadratic behavior: a thousand threads means a thousand stacks, so the > rendering of /proc//maps needs to look at a million threads. The > cost is not in proportion to the usefulness as described in the patch. > > Drop the [stack:TID] annotation to make /proc//maps (and > /proc//numa_maps) usable again for higher thread counts. > > The [stack] annotation inside /proc//task//maps is retained, > as identifying the stack VMA there is an O(1) operation. Four years ago, ouch. Any thoughts on the obvious back-compatibility concerns? ie, why did Siddhesh implement this in the first place? My bad for not ensuring that the changelog told us this. https://lkml.org/lkml/2012/1/14/25 has more info: : Memory mmaped by glibc for a thread stack currently shows up as a : simple anonymous map, which makes it difficult to differentiate between : memory usage of the thread on stack and other dynamic allocation. : Since glibc already uses MAP_STACK to request this mapping, the : attached patch uses this flag to add additional VM_STACK_FLAGS to the : resulting vma so that the mapping is treated as a stack and not any : regular anonymous mapping. Also, one may use vm_flags to decide if a : vma is a stack. But even that doesn't really tell us what the actual *value* of the patch is to end-users. I note that this patch is a partial revert - the smaps and numa_maps parts of b764375 remain in place. What's up with that?