From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi0-f70.google.com (mail-oi0-f70.google.com [209.85.218.70]) by kanga.kvack.org (Postfix) with ESMTP id 73D5E6B0069 for ; Mon, 22 Aug 2016 04:01:03 -0400 (EDT) Received: by mail-oi0-f70.google.com with SMTP id p18so295283422oic.0 for ; Mon, 22 Aug 2016 01:01:03 -0700 (PDT) Received: from smtprelay.hostedemail.com (smtprelay0182.hostedemail.com. [216.40.44.182]) by mx.google.com with ESMTPS id d75si15007175ith.69.2016.08.22.01.01.02 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 22 Aug 2016 01:01:02 -0700 (PDT) Message-ID: <1471852859.3746.42.camel@perches.com> Subject: Re: [PATCH 2/2] proc: task_mmu: Reduce output processing cpu time From: Joe Perches Date: Mon, 22 Aug 2016 01:00:59 -0700 In-Reply-To: <20160822072414.GB13596@dhcp22.suse.cz> References: <2c1ea0d8f35fa5ddea477369b273d6d91c5bf2e2.1471679737.git.joe@perches.com> <20160822072414.GB13596@dhcp22.suse.cz> Content-Type: text/plain; charset="ISO-8859-1" Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: linux-kernel@vger.kernel.org, Andrew Morton , Jann Horn , linux-mm@kvack.org On Mon, 2016-08-22 at 09:24 +0200, Michal Hocko wrote: > On Sat 20-08-16 01:00:17, Joe Perches wrote: > [...] > > > > static int proc_maps_open(struct inode *inode, struct file *file, > > const struct seq_operations *ops, int psize) > > { > > - struct proc_maps_private *priv = __seq_open_private(file, ops, psize); > > + struct proc_maps_private *priv; > > + struct mm_struct *mm; > > + > > + mm = proc_mem_open(inode, PTRACE_MODE_READ); > > + if (IS_ERR(mm)) > > + return PTR_ERR(mm); > > > > + priv = __seq_open_private_bufsize(file, ops, psize, > > + mm && mm->map_count ? > > + mm->map_count * 0x300 : PAGE_SIZE); > NAK to this! > > Seriously, this just gives any random user access to user > defined amount of memory which not accounted, not reclaimable and a > potential consumer of any higher order blocks. I completely disagree here with your rationale here. I think you didn't read the code and didn't try it either. This code is identical to the previous code but it simply estimates the required output size first. > Besides that, at least one show_smap output will always fit inside the > single page and AFAIR (it's been quite a while since I've looked into > seq_file internals) the buffer grows only when the single show doesn't > fit in. It's never been like that as far as I know. Please read fs/seq_file.c:traverse() This code starts with a PAGE_SIZE block of memory then if the complete output doesn't fit, stops, frees that block of memory, and retries the complete output with a last block size allocated << 1 and tries again. > I really do not understand why you insist on code duplication rather > than reuse but if you really insist then just make this (without the > above __seq_open_private_bufsize, re-measure and add the results to the > changelog and repost. I've tried it, I wish you would. -- 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