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Message-ID: <4F9EFF04.4040308@linaro.org>
Date: Mon, 30 Apr 2012 14:07:16 -0700
From: John Stultz <john.stultz@linaro.org>
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To: Dave Chinner <david@fromorbit.com>
CC: Dave Hansen <dave@linux.vnet.ibm.com>, LKML <linux-kernel@vger.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>, Rik van Riel <riel@redhat.com>,
        Dmitry Adamushko <dmitry.adamushko@gmail.com>,
        Neil Brown <neilb@suse.de>, Andrea Righi <andrea@betterlinux.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Subject: Re: [PATCH 2/3] fadvise: Add _VOLATILE,_ISVOLATILE, and _NONVOLATILE
 flags
References: <1335289787-11089-1-git-send-email-john.stultz@linaro.org> <1335289787-11089-3-git-send-email-john.stultz@linaro.org> <20120427003953.GC9541@dastard> <4F9ABA74.8040404@linux.vnet.ibm.com> <20120428013628.GJ9541@dastard>
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On 04/27/2012 06:36 PM, Dave Chinner wrote:
> That's my concern - that persistent filesystems will have different
> behaviour to in-memory filesystems. They *must* be consistent in
> behaviour w.r.t. to stale data exposure, otherwise we are in a world
> of pain when applications start to use this. Quite frankly, I don't
> care about performance of VOLATILE ranges, but I care greatly
> about ensuring filesystems don't expose stale data to user
> applications....
>
I think we're in agreement with the rest of this email, but I do want to 
stress that the performance of volatile ranges will become more 
ciritical, as in order for folks to effectively use them, they need to 
be able to mark and unmark ranges any time they're not using the data.

No application likely wants their data to be purged, but by volunteering 
it allows them to help the kernel with low-memory constraints and 
improve entire system behavior.

So if the overhead is too great for marking and unmarking pages, 
applications will be less likely to "help out".  :)

thanks
-john