linux-kernel - Re: [PATCH 0/4] promote zcache from staging

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Date:	Tue, 7 Aug 2012 15:28:07 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Dan Magenheimer <dan.magenheimer@...cle.com>,
	devel@...verdev.osuosl.org,
	Seth Jennings <sjenning@...ux.vnet.ibm.com>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Konrad Rzeszutek Wilk <konrad@...nok.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Robert Jennings <rcj@...ux.vnet.ibm.com>,
	Nitin Gupta <ngupta@...are.org>
Subject: Re: [PATCH 0/4] promote zcache from staging

On Mon, Aug 06, 2012 at 09:38:16AM +0900, Minchan Kim wrote:
> Hi Konrad,
> 
> On Tue, Jul 31, 2012 at 01:51:42PM -0400, Konrad Rzeszutek Wilk wrote:
> > On Tue, Jul 31, 2012 at 09:19:16AM -0700, Greg Kroah-Hartman wrote:
> > > On Tue, Jul 31, 2012 at 11:58:43AM -0400, Konrad Rzeszutek Wilk wrote:
> > > > So in my head I feel that it is Ok to:
> > > > 1) address the concerns that zcache has before it is unstaged
> > > > 2) rip out the two-engine system with a one-engine system
> > > >    (and see how well it behaves)
> > > > 3) sysfs->debugfs as needed
> > > > 4) other things as needed
> > > > 
> > > > I think we are getting hung-up what Greg said about adding features
> > > > and the two-engine->one engine could be understood as that.
> > > > While I think that is part of a staging effort to clean up the
> > > > existing issues. Lets see what Greg thinks.
> > > 
> > > Greg has no idea, except I want to see the needed fixups happen before
> > > new features get added.  Add the new features _after_ it is out of
> > > staging.
> > 
> > I think we (that is me, Seth, Minchan, Dan) need to talk to have a good
> > understanding of what each of us thinks are fixups.
> > 
> > Would Monday Aug 6th at 1pm EST on irc.freenode.net channel #zcache work
> > for people?
> 
> 1pm EST is 2am KST(Korea Standard Time) so it's not good for me. :)
> I know it's hard to adjust my time for yours so let you talk without
> me. Instead, I will write it down my requirement. It's very simple and
> trivial.

OK, Thank you.

We had a lengthy chat (full chat log attached). The summary was that
we all want to promote zcache (for various reasons), but we are hang up
whether we are OK unstaging it wherein it lowers the I/Os but potentially
not giving large performance increase (when doing 'make -jN') or that we
want both of those characteristics in. Little history: v3.3 had
swap readahead patches that made the amount of pages going in swap dramatically
decrease - as such the performance of zcache is not anymore amazing, but ok.

Seth and Robert (and I surmise Minchan too) are very interested in zcache
as its lowers the amount of I/Os but performance is secondary. Dan is interested
in having less I/Os and providing a performance boost with the such workloads as
'make -jN' - in short less I/Os and better performance. Dan would like both
before unstaging.

The action items that came out are:
 - Seth posted some benchmarks - he is going to rerun them with v3.5
   to see how it behaves in terms of performance (make -jN benchmark).
 - Robert is going to take a swing at Minchan refactor and adding comments, etc
   (But after we get over the hump of agreeing on the next step).
 - Konrad to rummage in his mbox to find any other technical objections
   that were raised on zcache earlier to make sure to address them.
 - Once Seth is finished Konrad is going to take another swing
   at driving this discussion - either via email, IRC or conference call.


View attachment "zcache-Aug6.log" of type "text/plain" (24124 bytes)