linux-kernel - RE: swap on eMMC and other flash

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Date:	Mon, 2 Apr 2012 12:52:04 +0000
From:	"Luca Porzio (lporzio)" <lporzio@...ron.com>
To:	Hugh Dickins <hughd@...gle.com>, Arnd Bergmann <arnd@...db.de>
CC:	Rik van Riel <riel@...hat.com>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Alex Lemberg <alex.lemberg@...disk.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Saugata Das <saugata.das@...aro.org>,
	Venkatraman S <venkat@...aro.org>,
	Yejin Moon <yejin.moon@...sung.com>,
	Hyojin Jeong <syr.jeong@...sung.com>,
	"linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
	"kernel-team@...roid.com" <kernel-team@...roid.com>
Subject: RE: swap on eMMC and other flash

Hugh,

Great topics. As per one of Rik original points:

> 4) skip writeout of zero-filled pages - this can be a big help
>     for KVM virtual machines running Windows, since Windows zeroes
>     out free pages;   simply discarding a zero-filled page is not
>     at all simple in the current VM, where we would have to iterate
>     over all the ptes to free the swap entry before being able to
>     free the swap cache page (I am not sure how that locking would
>     even work)
> 
>     with the extra layer of indirection, the locking for this scheme
>     can be trivial - either the faulting process gets the old page,
>     or it gets a new one, either way it'll be zero filled
> 

Since it's KVMs realm here, can't KSM simply solve the zero-filled pages problem avoiding unnecessary burden for the Swap subsystem?

Cheers, 
   Luca
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