linux-ext4 - Re: [PATCH 4/4] block: Optionally snapshot page contents to provide stable pages during write

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Date:	Mon, 17 Dec 2012 14:54:35 -0800
From:	"Darrick J. Wong" <darrick.wong@...cle.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	axboe@...nel.dk, lucho@...kov.net, jack@...e.cz, ericvh@...il.com,
	viro@...iv.linux.org.uk, rminnich@...dia.gov, tytso@....edu,
	martin.petersen@...cle.com, neilb@...e.de, david@...morbit.com,
	Zheng Liu <gnehzuil.liu@...il.com>,
	linux-kernel@...r.kernel.org, hch@...radead.org,
	linux-fsdevel@...r.kernel.org, adilger.kernel@...ger.ca,
	bharrosh@...asas.com, jlayton@...ba.org,
	v9fs-developer@...ts.sourceforge.net, linux-ext4@...r.kernel.org
Subject: Re: [PATCH 4/4] block: Optionally snapshot page contents to provide
 stable pages during write

On Fri, Dec 14, 2012 at 06:06:50PM -0800, Andy Lutomirski wrote:
> On Fri, Dec 14, 2012 at 6:01 PM, Darrick J. Wong
> <darrick.wong@...cle.com> wrote:
> > On Fri, Dec 14, 2012 at 05:12:37PM -0800, Andy Lutomirski wrote:
> >> It survived.  I hit at least one mm bug, but I really don't think it's
> >> a problem with your code.  (I have not tried this workload on Linux
> >> 3.7 at all before.  It normally runs on 3.5.)  The box in question is
> >
> > Would you mind sending along the bug report so I can make sure?
> 
> http://marc.info/?l=linux-mm&m=135553342803210&w=2

Hm, this looks like a hugepages thing, which (afaik) doesn't touch fs code at
all.  Looks like this patchset is in the clear.

> >
> >> ext4 on LVM on dm-crypt on (hardware) RAID 5 on hpsa, which should not
> >> need stable pages.
> >>
> >> The majority of the data written (that wasn't unlinked before it was
> >> dropped from cache) was checksummed when written and verified later.
> >> Most of this data was written using mmap.  This workload hammers the
> >> vm concurrently in several threads, and it frequently stalls when
> >> stable pages are enabled, so it's probably exercising the code
> >> decently well.
> >
> > Did you observe any change in performance?
> 
> No.  But I'm comparing to 3.5 + butchery to remove stable pages.  With
> stable pages on, this workload performs terribly.  (It's a soft
> real-time thing, as you can possibly guess from my domain name, and
> various latency monitoring things go nuts when stable pages are
> active.)

Well, I guess that's good. :)

> Actually, performance appears to be improved, probably due to
> https://lkml.org/lkml/2012/12/14/14, which I tested concurrently.
> 
> >
> >> Feel free to add Tested-by: Andy Lutomirski <luto@...capital.net>
> >
> > Will do!  Thanks for the testing!
> 
> My pleasure.  When these changes go in to an upstream kernel, they'll
> represent a significant reduction in how much our kernel differs from
> kernel.org's :)  Thanks for fixing this.

No problem!

--D
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