Message-ID: <52534AEC.5040403@zytor.com>
Date: Mon, 07 Oct 2013 16:59:40 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130625 Thunderbird/17.0.7
MIME-Version: 1.0
To: John Stultz <john.stultz@linaro.org>
CC: LKML <linux-kernel@vger.kernel.org>, Minchan Kim <minchan@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Android Kernel Team <kernel-team@android.com>,
        Robert Love <rlove@google.com>, Mel Gorman <mel@csn.ul.ie>,
        Hugh Dickins <hughd@google.com>, Dave Hansen <dave.hansen@intel.com>,
        Rik van Riel <riel@redhat.com>,
        Dmitry Adamushko <dmitry.adamushko@gmail.com>,
        Dave Chinner <david@fromorbit.com>, Neil Brown <neilb@suse.de>,
        Andrea Righi <andrea@betterlinux.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>,
        Mike Hommey <mh@glandium.org>, Taras Glek <tglek@mozilla.com>,
        Dhaval Giani <dhaval.giani@gmail.com>, Jan Kara <jack@suse.cz>,
        KOSAKI Motohiro <kosaki.motohiro@gmail.com>,
        Michel Lespinasse <walken@google.com>, Rob Clark <robdclark@gmail.com>,
        "linux-mm@kvack.org" <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>
In-Reply-To: <525349AE.1070904@linaro.org>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1655
Lines: 37

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 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/