From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f42.google.com (mail-wm0-f42.google.com [74.125.82.42]) by kanga.kvack.org (Postfix) with ESMTP id D5C6A6B0005 for ; Tue, 19 Jan 2016 18:30:31 -0500 (EST) Received: by mail-wm0-f42.google.com with SMTP id 123so111850674wmz.0 for ; Tue, 19 Jan 2016 15:30:31 -0800 (PST) Received: from mail-wm0-x230.google.com (mail-wm0-x230.google.com. [2a00:1450:400c:c09::230]) by mx.google.com with ESMTPS id l141si36550718wmd.81.2016.01.19.15.30.30 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 19 Jan 2016 15:30:30 -0800 (PST) Received: by mail-wm0-x230.google.com with SMTP id 123so111850386wmz.0 for ; Tue, 19 Jan 2016 15:30:30 -0800 (PST) Date: Wed, 20 Jan 2016 01:30:28 +0200 From: "Kirill A. Shutemov" Subject: Re: [PATCH] proc: revert /proc//maps [stack:TID] annotation Message-ID: <20160119233028.GA22867@node.shutemov.name> References: <1453226559-17322-1-git-send-email-hannes@cmpxchg.org> <20160119141430.8ff9c464.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160119141430.8ff9c464.akpm@linux-foundation.org> Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Johannes Weiner , Shaohua Li , Siddhesh Poyarekar , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@fb.com On Tue, Jan 19, 2016 at 02:14:30PM -0800, Andrew Morton wrote: > 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 doubt it can be very useful as it's unreliable: if two stacks are allocated end-to-end (which is not good idea, but still) it can only report [stack:XXX] for the first one as they are merged into one VMA. Any other anon VMA merged with the stack will be also claimed as stack, which is not always correct. I think report the VMA as anon is the best we can know about it, everything else just rather expensive guesses. > 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? > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@kvack.org. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: email@kvack.org -- Kirill A. Shutemov -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org