From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759536AbcIWMOJ (ORCPT ); Fri, 23 Sep 2016 08:14:09 -0400 Received: from merlin.infradead.org ([205.233.59.134]:49058 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759473AbcIWMOH (ORCPT ); Fri, 23 Sep 2016 08:14:07 -0400 Date: Fri, 23 Sep 2016 14:14:03 +0200 From: Peter Zijlstra To: Alexander Shishkin Cc: Ingo Molnar , linux-kernel@vger.kernel.org, vince@deater.net, eranian@google.com, Arnaldo Carvalho de Melo , tglx@linutronix.de, ak@linux.intel.com Subject: Re: [RFC PATCH 1/6] perf: Move mlock accounting to ring buffer allocation Message-ID: <20160923121403.GC5012@twins.programming.kicks-ass.net> References: <20160923112726.5890-1-alexander.shishkin@linux.intel.com> <20160923112726.5890-2-alexander.shishkin@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160923112726.5890-2-alexander.shishkin@linux.intel.com> User-Agent: Mutt/1.5.23.1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Sep 23, 2016 at 02:27:21PM +0300, Alexander Shishkin wrote: > In order to be able to allocate perf ring buffers in non-mmap path, we > need to make sure we can still account the memory to the user and that > they don't exceed their mlock limit. > > This patch moves ring buffer memory accounting down the rb_alloc() path > so that its callers won't have to worry about it. This also serves the > additional purpose of slightly cleaning up perf_mmap(). While I like a cleanup of that code (it really can use one), I'm not a big fan of hidden buffers like this. Why is this needed? A quick look through the patches also leaves me wondering on the design and interface of this thing. A few words explaining the overall design would be nice. Afaict there's no actual need to hide the AUX buffer for this sampling stuff; the user knows about all this and can simply mmap() the AUX part. The sample could either point to locations in the AUX buffer, or (as I think this code does) memcpy bits out. Ideally we'd pass the AUX-event into the syscall, that way you avoid all the find_aux_event crud. I'm not sure we want to overload the group_fd thing more (its already very hard to create counter groups in a cgroup for example) .. Coredump was mentioned somewhere, but I'm not sure I've seen code/interfaces for that. How was that envisioned to work?