linux-kernel - Re: mmap dirty limits on 32 bit kernels (Was: [BUG] New Kernel Bugs)

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Message-ID: <20071119034129.GA15954@brong.net>
Date:	Mon, 19 Nov 2007 14:41:29 +1100
From:	Bron Gondwana <brong@...tmail.fm>
To:	Daniel Phillips <phillips@...nq.net>
Cc:	Rob Mueller <robm@...tmail.fm>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Bron Gondwana <brong@...tmail.fm>,
	Christian Kujau <lists@...dbynature.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	riel <riel@...hat.com>, Anton Altaparmakov <aia21@....ac.uk>
Subject: Re: mmap dirty limits on 32 bit kernels (Was: [BUG] New Kernel
	Bugs)

On Sun, Nov 18, 2007 at 04:13:18PM -0700, Daniel Phillips wrote:
> On Thursday 15 November 2007 14:24, Rob Mueller wrote:
> > > That's my personal opinion, and I realize that some of the
> > > commercial vendors may care about their insane customers'
> > > satisfaction, but I'm simply not interested in insane users. If
> > > they have that much RAM (and bought it a few years ago when a
> > > 64-bit CPU wasn't an option), they can't be poor.
> >
> > From our perspective, the main issue is that some of these machines
> > we spent quite a bit of money on the big RAM (for it's day) + lots of
> > 15k RPM SCSI drives + multi-year support contracts. They're highly IO
> > bound, and barely use 10-20% of their old 2.4Ghz Prestonia Xeon CPUs.
> > It's hard to justify junking those machines < 5 years.
> >
> > We have a couple of 6G machines and some 8G machines using PAE. On
> > the whole, they actually have been working really well (hmmm, apart
> > from the recent dirty pages issue + reiserfs data=journal leaks +
> > inodes in lowmem limits)
> 
> Junk everything except the 15K drives, you will be glad you did.  Too 
> bad about those multi-year support contracts, hopefully you got a deal 
> on them.

Actually, the 15K drives are the bit we're getting the least use out
of now, since we're moving everything to external SATA units that
are more easily swapable.
 
> Prediction: after these dirty pages issues are gone, there will be more 
> dirty page issues because the notion of dirty page limit is 
> fundamentally broken.  Your smartest recourse is to re-motherboard to a 
> place where the dirty page limit borkage does not hurt as much, and in 
> the process you will get a cheap hardware upgrade.  Everybody will be 
> happy, the sun will come out, the birds will sing.

Or just keep running 2.6.16 where it's all been working quite fine
thanks very much, or maintain a simple patch that rips all that out
since we don't care too much about "fairness" - we only run a couple
of things on that machine and they run fine.

Bron ( going to settle down and really test this stuff to make sure
       we have an acceptable "fix" for us then do it! )
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