linux-kernel - Re: [PATCH 3/3] [RFC] tmpfs: Add FALLOC_FL_MARK_VOLATILE/UNMARK

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Message-ID: <4FD16B6E.8000307@linaro.org>
Date:	Thu, 07 Jun 2012 20:03:10 -0700
From:	John Stultz <john.stultz@...aro.org>
To:	Dave Hansen <dave@...ux.vnet.ibm.com>
CC:	Dmitry Adamushko <dmitry.adamushko@...il.com>,
	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Android Kernel Team <kernel-team@...roid.com>,
	Robert Love <rlove@...gle.com>, Mel Gorman <mel@....ul.ie>,
	Hugh Dickins <hughd@...gle.com>,
	Rik van Riel <riel@...hat.com>,
	Dave Chinner <david@...morbit.com>, Neil Brown <neilb@...e.de>,
	Andrea Righi <andrea@...terlinux.com>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Taras Glek <tgek@...illa.com>, Mike Hommey <mh@...ndium.org>,
	Jan Kara <jack@...e.cz>
Subject: Re: [PATCH 3/3] [RFC] tmpfs: Add FALLOC_FL_MARK_VOLATILE/UNMARK_VOLATILE
 handlers

On 06/07/2012 04:41 PM, Dave Hansen wrote:
> On 06/07/2012 03:55 AM, Dmitry Adamushko wrote:
>> but maybe we should also purge them before we swap out some non-tmpfs
>> pages or drop some file-backed pages?
>
> Sure...  I guess we could kick that from either direct reclaim or from
> kswapd.  But, then we're basically back to the places where
> shrink_slab() is called.
>
> I think that means that we think it's preferable to integrate this more
> directly in the VM instead of sticking it off in the corner of tmpfs
> only, or pretending it's a slab.
>
> Dunno...  The slab shrinker one isn't looking _so_ bad at the moment.

Dave also pointed out to me on irc that on a system without swap, 
shmem_writepage doesn't even get called, which kills the utility of 
triggering volatile purging from writepage.

So I'm falling back to using a shrinker for now, but I think Dmitry's 
point is an interesting one, and am interested in finding a better place 
to trigger purging volatile ranges from the mm code. If anyone has any 
suggestions, let me know, otherwise I'll go back to trying to better 
grok the mm code.

thanks
-john


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