linux-kernel - Re: [PATCH V10 0/6] mm: frontswap: overview (and proposal to merge at next window)

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Date:	Thu, 29 Sep 2011 13:48:16 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Dan Magenheimer <dan.magenheimer@...cle.com>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org, jeremy@...p.org,
	hughd@...gle.com, ngupta@...are.org,
	Konrad Wilk <konrad.wilk@...cle.com>, JBeulich@...ell.com,
	Kurt Hackel <kurt.hackel@...cle.com>, npiggin@...nel.dk,
	akpm@...ux-foundation.org, riel@...hat.com, hannes@...xchg.org,
	matthew@....cx, Chris Mason <chris.mason@...cle.com>,
	sjenning@...ux.vnet.ibm.com, jackdachef@...il.com,
	cyclonusj@...il.com, levinsasha928@...il.com
Subject: Re: [PATCH V10 0/6] mm: frontswap: overview (and proposal to merge
 at next window)

On Wed, 28 Sep 2011 07:09:18 -0700 (PDT)
Dan Magenheimer <dan.magenheimer@...cle.com> wrote:

> > From: KAMEZAWA Hiroyuki [mailto:kamezawa.hiroyu@...fujitsu.com]
> > Sent: Wednesday, September 28, 2011 12:16 AM
> > To: Dan Magenheimer
> > Cc: linux-kernel@...r.kernel.org; linux-mm@...ck.org; jeremy@...p.org; hughd@...gle.com;
> > ngupta@...are.org; Konrad Wilk; JBeulich@...ell.com; Kurt Hackel; npiggin@...nel.dk; akpm@...ux-
> > foundation.org; riel@...hat.com; hannes@...xchg.org; matthew@....cx; Chris Mason;
> > sjenning@...ux.vnet.ibm.com; jackdachef@...il.com; cyclonusj@...il.com; levinsasha928@...il.com
> > Subject: Re: [PATCH V10 0/6] mm: frontswap: overview (and proposal to merge at next window)
> > 
> > On Thu, 15 Sep 2011 14:33:05 -0700
> > Dan Magenheimer <dan.magenheimer@...cle.com> wrote:
> > 
> > > [PATCH V10 0/6] mm: frontswap: overview (and proposal to merge at next window)
> > >
> > > (Note: V9->V10 only change is corrections in debugfs-related code/counters)
> > >
> > > (Note to earlier reviewers:  This patchset was reorganized at V9 due
> > > to feedback from Kame Hiroyuki and Andrew Morton.  Additionally, feedback
> > > on frontswap v8 from Andrew Morton also applies to cleancache, to wit:
> > >  (1) change usage of sysfs to debugfs to avoid unnecessary kernel ABIs
> > >  (2) rename all uses of "flush" to "invalidate"
> > > As a result, additional patches (5of6 and 6of6) were added to this
> > > series at V9 to patch cleancache core code and cleancache hooks in the mm
> > > and fs subsystems and update cleancache documentation accordingly.)
> > 
> > I'm sorry I couldn't catch following... what happens at hibernation ?
> > frontswap is effectively stopped/skipped automatically ? or contents of
> > TMEM can be kept after power off and it can be read correctly when
> > resume thread reads swap ?
> > 
> > In short: no influence to hibernation ?
> > I'm sorry if I misunderstand some.
> 
> Hi Kame --
> 
> Hibernation would need to be handled by the tmem backend (e.g. zcache, Xen
> tmem).  In the case of Xen tmem, both save/restore and live migration are
> fully supported.  I'm not sure if zcache works across hibernation; since
> all memory is kmalloc'ed, I think it should work fine, but it would be an
> interesting experiment.
> 

I'm afraid that users will lose data on memory of frontswap/zcache/tmem
by power-off, hibernation. How about adding internal hooks to disable/sync
frontswap itself before hibernation ? difficult ?

Thanks,
-Kame



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