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From: dean gaudet <dean@arctic.org>
To: Neil Brown <neilb@suse.de>
Cc: linux-kernel@vger.kernel.org
Subject: Re: [PATCH - RFC] allow setting vm_dirty below 1% for large memory machines
Date: Thu, 11 Jan 2007 03:04:00 -0800 (PST)	[thread overview]
Message-ID: <Pine.LNX.4.64.0701110245300.22043@twinlark.arctic.org> (raw)
In-Reply-To: <17827.22798.625018.673326@notabene.brown>

On Tue, 9 Jan 2007, Neil Brown wrote:

> Imagine a machine with lots of memory - say 100Gig.

i've had these problems on machines as "small" as 8GiB.  the real problem 
is that the kernel will let millions of potential (write) IO ops stack up 
for a device which can handle only mere 100s of IOs per second.  (and i'm 
not convinced it does the IOs in a sane order when it has millions to 
choose from)

replacing the percentage based dirty_ratio / dirty_background_ratio with 
sane kibibyte units is a good fix... but i'm not sure it's sufficient.

it seems like the "flow control" mechanism (i.e. dirty_ratio) should be on 
a device basis...

try running doug ledford'd memtest.sh on an 8GiB box with a single disk, 
let it go a few minutes then ^C and type "sync".  i've had to wait 10 
minutes (2.6.18 with default vm settings).

it makes it hard to guarantee a box can shutdown quickly -- nasty for 
setting up UPS on-battery timeouts for example.

-dean

  parent reply	other threads:[~2007-01-11 11:04 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-01-09  8:57 Neil Brown
2007-01-09 10:10 ` Andrew Morton
2007-01-10  3:04   ` Neil Brown
2007-01-10  3:29   ` Neil Brown
2007-01-10  3:41     ` Andrew Morton
2007-01-11 11:04 ` dean gaudet [this message]
2007-01-11 20:21   ` Andrew Morton
2007-01-11 22:35     ` dean gaudet
2007-01-11 22:48       ` Andrew Morton
2007-03-07 10:23         ` Leroy van Logchem

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