From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pd0-f171.google.com (mail-pd0-f171.google.com [209.85.192.171]) by kanga.kvack.org (Postfix) with ESMTP id 3BFBD6B0037 for ; Mon, 7 Oct 2013 20:00:36 -0400 (EDT) Received: by mail-pd0-f171.google.com with SMTP id g10so7807138pdj.30 for ; Mon, 07 Oct 2013 17:00:35 -0700 (PDT) Message-ID: <52534AEC.5040403@zytor.com> Date: Mon, 07 Oct 2013 16:59:40 -0700 From: "H. Peter Anvin" MIME-Version: 1.0 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> In-Reply-To: <525349AE.1070904@linaro.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: John Stultz Cc: LKML , Minchan Kim , 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" 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. -0hpa -- 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