Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754552Ab2KBU7i (ORCPT ); Fri, 2 Nov 2012 16:59:38 -0400 Received: from mail-oa0-f46.google.com ([209.85.219.46]:46791 "EHLO mail-oa0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754019Ab2KBU72 (ORCPT ); Fri, 2 Nov 2012 16:59:28 -0400 MIME-Version: 1.0 In-Reply-To: <506B6CE0.1060800@linaro.org> References: <1348888593-23047-1-git-send-email-john.stultz@linaro.org> <20121002173928.2062004e@notabene.brown> <506B6CE0.1060800@linaro.org> From: Michael Kerrisk Date: Fri, 2 Nov 2012 21:59:07 +0100 X-Google-Sender-Auth: 2Vl-W_VoN2d6mfariwlWRPeCKAs Message-ID: Subject: Re: [PATCH 0/3] Volatile Ranges (v7) & Lots of words To: John Stultz Cc: NeilBrown , LKML , Andrew Morton , Android Kernel Team , Robert Love , Mel Gorman , Hugh Dickins , Dave Hansen , Rik van Riel , Dmitry Adamushko , Dave Chinner , Andrea Righi , "Aneesh Kumar K.V" , Mike Hommey , Taras Glek , Jan Kara , KOSAKI Motohiro , Michel Lespinasse , Minchan Kim , "linux-mm@kvack.org" , Christoph Hellwig Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1851 Lines: 42 John, A question at on one point: On Wed, Oct 3, 2012 at 12:38 AM, John Stultz wrote: > On 10/02/2012 12:39 AM, NeilBrown wrote: [...] >> The SIGBUS interface could have some merit if it really reduces >> overhead. I >> worry about app bugs that could result from the non-deterministic >> behaviour. A range could get unmapped while it is in use and testing >> for >> the case of "get a SIGBUS half way though accessing something" would not >> be straight forward (SIGBUS on first step of access should be easy). >> I guess that is up to the app writer, but I have never liked anything >> about >> the signal interface and encouraging further use doesn't feel wise. > > Initially I didn't like the idea, but have warmed considerably to it. Mainly > due to the concern that the constant unmark/access/mark pattern would be too > much overhead, and having a lazy method will be much nicer for performance. > But yes, at the cost of additional complexity of handling the signal, > marking the faulted address range as non-volatile, restoring the data and > continuing. At a finer level of detail, how do you see this as happening in the application. I mean: in the general case, repopulating the purged volatile page would have to be done outside the signal handler (I think, because async-signal-safety considerations would preclude too much compdex stuff going on inside the handler). That implies longjumping out of the handler, repopulating the pages with data, and then restarting whatever work was being done when the SIGBUS was generated. Cheers, Michael -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/