Message-ID: <52534331.2060402@zytor.com>
Date: Mon, 07 Oct 2013 16:26:41 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
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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>
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On 10/07/2013 04:14 PM, John Stultz wrote:
>>
>> I see from the change history of the patch that this was an madvise() at
>> some point, but was changed into a separate system call at some point,
>> does anyone remember why that was?  A quick look through my LKML
>> archives doesn't really make it clear.
> 
> The reason we can't use madvise, is that to properly handle error cases
> and report the pruge state, we need an extra argument.
> 
> In much earlier versions, we just returned an error when setting
> NONVOLATILE if the data was purged. However, since we have to possibly
> do allocations when marking a range as non-volatile, we needed a way to
> properly handle that allocation failing. We can't just return ENOMEM, as
> we may have already marked purged memory as non-volatile.
> 
> Thus, that's why with vrange, we return the number of bytes modified,
> along with the purge state. That way, if an error does occur we can
> return the purge state of the bytes successfully modified, and only
> return an error if nothing was changed, much like when a write fails.
> 

I am not clear at all what the "purge state" is in this case.

	-hpa


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