From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S966446AbcIZMkc (ORCPT ); Mon, 26 Sep 2016 08:40:32 -0400 Received: from mga01.intel.com ([192.55.52.88]:18618 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965304AbcIZMk2 (ORCPT ); Mon, 26 Sep 2016 08:40:28 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.30,399,1470726000"; d="scan'208";a="1056719347" From: Alexander Shishkin To: Peter Zijlstra Cc: Andi Kleen , Ingo Molnar , linux-kernel@vger.kernel.org, vince@deater.net, eranian@google.com, Arnaldo Carvalho de Melo , tglx@linutronix.de Subject: Re: [RFC PATCH 1/6] perf: Move mlock accounting to ring buffer allocation In-Reply-To: <20160926090354.GK5012@twins.programming.kicks-ass.net> References: <20160923112726.5890-1-alexander.shishkin@linux.intel.com> <20160923112726.5890-2-alexander.shishkin@linux.intel.com> <20160923121403.GC5012@twins.programming.kicks-ass.net> <20160923172615.GU3078@tassilo.jf.intel.com> <20160923202830.GQ5008@twins.programming.kicks-ass.net> <878tufrrqb.fsf@ashishki-desk.ger.corp.intel.com> <20160926090354.GK5012@twins.programming.kicks-ass.net> User-Agent: Notmuch/0.22.1 (http://notmuchmail.org) Emacs/24.5.1 (x86_64-pc-linux-gnu) Date: Mon, 26 Sep 2016 15:39:49 +0300 Message-ID: <87y42erg16.fsf@ashishki-desk.ger.corp.intel.com> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Peter Zijlstra writes: > On Mon, Sep 26, 2016 at 11:27:08AM +0300, Alexander Shishkin wrote: >> Peter Zijlstra writes: >> > At which point we _should_ start failing fork(), which is a somewhat >> > unexpected, and undesirable side-effect. >> >> I'm not sure I see why we should fail fork() when we run out of pinned >> memory. > > Well, we cannot fully honour the inherit, what other option do we have? > Silently malfunctioning? That's far worse. We can still put a note there saying that we tried. The user will know to adjust their buffer size requirement or the RLIMIT_MEMLOCK. >> > Ideally we'd unpin the old buffers and repin the new buffers on context >> > switch, but that's impossible since faulting needs scheduling, >> > recursion, we loose. >> >> Or we can have per-cpu buffers for all user's tasks, record where each >> task starts and ends in each buffer and cut out only bits relevant to >> the task(s) that dump core. > > Which gets you the problem that when a task dumps core there might not > be any state in the buffer, because the previous task flushed it all out > :/ Well, there's going to be at list something that leads up to the core dump if this task is the last one to schedule in for this buffer. It's a bit more gambling, though. Regards, -- Alex