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

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Date:	Fri, 17 Aug 2012 15:21:22 -0700 (PDT)
From:	Dan Magenheimer <dan.magenheimer@...cle.com>
To:	Seth Jennings <sjenning@...ux.vnet.ibm.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Nitin Gupta <ngupta@...are.org>,
	Minchan Kim <minchan@...nel.org>,
	Konrad Wilk <konrad.wilk@...cle.com>,
	Robert Jennings <rcj@...ux.vnet.ibm.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, devel@...verdev.osuosl.org,
	Kurt Hackel <kurt.hackel@...cle.com>
Subject: RE: [PATCH 0/4] promote zcache from staging

> From: Seth Jennings [mailto:sjenning@...ux.vnet.ibm.com]
> Subject: Re: [PATCH 0/4] promote zcache from staging
> 
> On 08/09/2012 03:20 PM, Dan Magenheimer wrote
> > I also wonder if you have anything else unusual in your
> > test setup, such as a fast swap disk (mine is a partition
> > on the same rotating disk as source and target of the kernel build,
> > the default install for a RHEL6 system)?
> 
> I'm using a normal SATA HDD with two partitions, one for
> swap and the other an ext3 filesystem with the kernel source.
> 
> > Or have you disabled cleancache?
> 
> Yes, I _did_ disable cleancache.  I could see where having
> cleancache enabled could explain the difference in results.

Sorry to beat a dead horse, but I meant to report this
earlier in the week and got tied up by other things.

I finally got my test scaffold set up earlier this week
to try to reproduce my "bad" numbers with the RHEL6-ish
config file.

I found that with "make -j28" and "make -j32" I experienced
__DATA CORRUPTION__.  This was repeatable.

The type of error led me to believe that the problem was
due to concurrency of cleancache reclaim.  I did not try
with cleancache disabled to prove/support this theory
but it is consistent with the fact that you (Seth) have not
seen a similar problem and has disabled cleancache.

While this problem is most likely in my code and I am
suitably chagrined, it re-emphasizes the fact that
the current zcache in staging is 20-month old "demo"
code.  The proposed new zcache codebase handles concurrency
much more effectively.

I'll be away from email for a few days now.

Dan
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