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

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

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

> > From: KAMEZAWA Hiroyuki [mailto:kamezawa.hiroyu@jp.fujitsu.com]
> > Sent: Wednesday, September 28, 2011 12:16 AM
> > To: Dan Magenheimer
> > Cc: linux-kernel@vger.kernel.org; linux-mm@kvack.org; jeremy@goop.org; hughd@google.com;
> > ngupta@vflare.org; Konrad Wilk; JBeulich@novell.com; Kurt Hackel; npiggin@kernel.dk; akpm@linux-
> > foundation.org; riel@redhat.com; hannes@cmpxchg.org; matthew@wil.cx; Chris Mason;
> > sjenning@linux.vnet.ibm.com; jackdachef@gmail.com; cyclonusj@gmail.com; levinsasha928@gmail.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@oracle.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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