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    SubjectRe: [PATCH 0/4] promote zcache from staging
    On 08/17/2012 05:21 PM, Dan Magenheimer wrote:
    >> From: Seth Jennings [mailto:sjenning@linux.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.

    I actually hit this for the first time a few hours ago when
    I was running performance for your rewrite. I didn't know
    what to make of it yet. The 24-thread kernel build failed
    when both frontswap and cleancache were enabled.

    > 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 imagine this can be solved without rewriting the entire
    codebase. If your new code contains a fix for this, can we
    just pull it as a single patch?

    Seth



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