Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753531Ab3JHASr (ORCPT ); Mon, 7 Oct 2013 20:18:47 -0400 Received: from mail-pa0-f42.google.com ([209.85.220.42]:60293 "EHLO mail-pa0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751885Ab3JHASp (ORCPT ); Mon, 7 Oct 2013 20:18:45 -0400 Message-ID: <52534F60.9030500@linaro.org> Date: Mon, 07 Oct 2013 17:18:40 -0700 From: John Stultz User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.0 MIME-Version: 1.0 To: Minchan Kim , "H. Peter Anvin" CC: LKML , Andrew Morton , Android Kernel Team , Robert Love , Mel Gorman , Hugh Dickins , Dave Hansen , Rik van Riel , Dmitry Adamushko , Dave Chinner , Neil Brown , Andrea Righi , Andrea Arcangeli , "Aneesh Kumar K.V" , Mike Hommey , Taras Glek , Dhaval Giani , Jan Kara , KOSAKI Motohiro , Michel Lespinasse , Rob Clark , "linux-mm@kvack.org" Subject: Re: [PATCH 05/14] vrange: Add new vrange(2) system call References: <1380761503-14509-1-git-send-email-john.stultz@linaro.org> <1380761503-14509-6-git-send-email-john.stultz@linaro.org> <52533C12.9090007@zytor.com> <5253404D.2030503@linaro.org> <52534331.2060402@zytor.com> <52534692.7010400@linaro.org> <525347BE.7040606@zytor.com> <525349AE.1070904@linaro.org> <52534AEC.5040403@zytor.com> <20131008001306.GD25780@bbox> In-Reply-To: <20131008001306.GD25780@bbox> X-Enigmail-Version: 1.5.2 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2589 Lines: 53 On 10/07/2013 05:13 PM, Minchan Kim wrote: > Hello Peter, > > On Mon, Oct 07, 2013 at 04:59:40PM -0700, H. Peter Anvin wrote: >> On 10/07/2013 04:54 PM, John Stultz wrote: >>>> And wouldn't this apply to MADV_DONTNEED just as well? Perhaps what we >>>> should do is an enhanced madvise() call? >>> Well, I think MADV_DONTNEED doesn't *have* do to anything at all. Its >>> advisory after all. So it may immediately wipe out any data, but it may not. >>> >>> Those advisory semantics work fine w/ VRANGE_VOLATILE. However, >>> VRANGE_NONVOLATILE is not quite advisory, its telling the system that it >>> requires the memory at the specified range to not be volatile, and we >>> need to correctly inform userland how much was changed and if any of the >>> memory we did change to non-volatile was purged since being set volatile. >>> >>> In that way it is sort of different from madvise. Some sort of an >>> madvise2 could be done, but then the extra purge state argument would be >>> oddly defined for any other mode. >>> >>> Is your main concern here just wanting to have a zero-fill mode with >>> volatile ranges? Or do you really want to squeeze this in to the madvise >>> call interface? >> The point is that MADV_DONTNEED is very similar in that sense, >> especially if allowed to be lazy. It makes a lot of sense to permit >> both scrubbing modes orthogonally. >> >> The point you're making has to do with withdrawal of permission to flush >> on demand, which is a result of having the lazy mode (ongoing >> permission) and having to be able to withdraw such permission. > I'm sorry I could not understand what you wanted to say. > Could you elaborate a bit? My understanding of his point is that VRANGE_VOLATILE is like a lazy MADV_DONTNEED (with sigbus, rather then zero fill on fault), suggests that we should find a way to have VRANGE_VOLATILE be something like MADV_DONTNEED|MADV_LAZY|MADV_SIGBUS_FAULT, instead of adding a new syscall. This would provide more options, since one could instead just do MADV_DONTNEED|MADV_LAZY if they wanted zero-fill faults. And indeed, for the VRANGE_VOLATILE case, we could do something like that, but the unresolved problem I see is that that we still need to handle the VRANGE_NONVOLATILE case, and the madvise() interface doesn't seem to accomodate the needed semantics well. thanks -john -- 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/