From: John Stoffel <stoffel@casc.com>
To: Rik van Riel <riel@conectiva.com.br>
Cc: John Stoffel <stoffel@casc.com>,
Roger Larsson <roger.larsson@norran.net>,
Daniel Phillips <phillips@bonn-fries.net>,
Linux-Kernel <linux-kernel@vger.kernel.org>
Subject: Re: 2.4.6-pre2, pre3 VM Behavior
Date: Thu, 14 Jun 2001 17:33:23 -0400 [thread overview]
Message-ID: <15145.11683.861734.853957@gargle.gargle.HOWL> (raw)
In-Reply-To: <Pine.LNX.4.33.0106141750260.28370-100000@duckman.distro.conectiva>
In-Reply-To: <15145.8435.312548.682190@gargle.gargle.HOWL> <Pine.LNX.4.33.0106141750260.28370-100000@duckman.distro.conectiva>
Rik> There's another issue. If dirty data is written out in small
Rik> bunches, that means we have to write out the dirty data more
Rik> often.
What do you consider a small bunch? 32k? 1Mb? 1% of buffer space?
I don't see how delaying writes until the buffer is almost full really
helps us. As the buffer fills, the pressure to do writes should
increase, so that we tend, over time, to empty the buffer.
A buffer is just that, not persistent storage.
And in the case given, we were not seeing slow degradation, we saw
that the user ran into a wall (or inflection point in the response
time vs load graph), which was pretty sharp. We need to handle that
more gracefully.
Rik> This in turn means extra disk seeks, which can horribly interfere
Rik> with disk reads.
True, but are we optomizing for reads or for writes here? Shouldn't
they really be equally weighted for priority? And wouldn't the
Elevator help handle this to a degree?
Some areas to think about, at least for me. And maybe it should be
read and write pressure, not rate?
- low write rate, and a low read rate.
- Do seeks dominate our IO latency/throughput?
- low read rate, higher write rate (ie buffers filling faster than
they are being written to disk)
- Do we care as much about reads in this case?
- If the write is just a small, high intensity burst, we don't want
to go ape on writing out buffers to disk, but we do want to raise the
rate we do so in the background, no?
- low write rate, high read rate.
- seems like we want to keep writing the buffers, but at a lower
rate.
Just some thoughts...
John
John Stoffel - Senior Unix Systems Administrator - Lucent Technologies
stoffel@lucent.com - http://www.lucent.com - 978-952-7548
next prev parent reply other threads:[~2001-06-14 21:34 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2001-06-13 19:31 2.4.6-pre2, pre3 VM Behavior Tom Sightler
2001-06-13 20:21 ` Rik van Riel
2001-06-14 1:49 ` Tom Sightler
2001-06-14 3:16 ` Rik van Riel
2001-06-14 7:59 ` Laramie Leavitt
2001-06-14 9:24 ` Helge Hafting
2001-06-14 17:38 ` Mark Hahn
2001-06-15 8:27 ` Helge Hafting
2001-06-14 8:47 ` Daniel Phillips
2001-06-14 20:23 ` Roger Larsson
2001-06-15 6:04 ` Mike Galbraith
2001-06-14 20:39 ` John Stoffel
2001-06-14 20:51 ` Rik van Riel
2001-06-14 21:33 ` John Stoffel [this message]
2001-06-14 22:23 ` Rik van Riel
2001-06-15 15:23 ` spindown [was Re: 2.4.6-pre2, pre3 VM Behavior] Pavel Machek
2001-06-16 20:50 ` Daniel Phillips
2001-06-16 21:06 ` Rik van Riel
2001-06-16 21:25 ` Rik van Riel
2001-06-16 21:44 ` Daniel Phillips
2001-06-16 21:54 ` Rik van Riel
2001-06-17 10:28 ` Daniel Phillips
2001-06-17 10:05 ` Mike Galbraith
2001-06-17 12:49 ` (lkml)Re: " thunder7
2001-06-17 16:40 ` Mike Galbraith
2001-06-18 14:22 ` Daniel Phillips
2001-06-19 4:35 ` Mike Galbraith
2001-06-20 1:50 ` [RFC] Early flush (was: spindown) Daniel Phillips
2001-06-20 20:58 ` Tom Sightler
2001-06-20 22:09 ` Daniel Phillips
2001-06-24 3:20 ` Anuradha Ratnaweera
2001-06-24 11:14 ` Daniel Phillips
2001-06-24 15:06 ` Rik van Riel
2001-06-24 16:21 ` Daniel Phillips
2001-06-20 4:39 ` Richard Gooch
2001-06-20 14:29 ` Daniel Phillips
2001-06-20 16:12 ` Richard Gooch
2001-06-22 23:25 ` Daniel Kobras
2001-06-23 5:10 ` Daniel Phillips
2001-06-25 11:33 ` Pavel Machek
2001-06-25 11:31 ` Pavel Machek
2001-06-18 20:21 ` spindown Simon Huggins
2001-06-19 10:46 ` spindown Pavel Machek
2001-06-20 16:52 ` spindown Daniel Phillips
2001-06-20 17:32 ` spindown Rik van Riel
2001-06-20 18:00 ` spindown Daniel Phillips
2001-06-21 16:07 ` spindown Jamie Lokier
2001-06-22 22:09 ` spindown Daniel Kobras
2001-06-28 0:27 ` spindown Troy Benjegerdes
2001-06-14 15:10 ` 2.4.6-pre2, pre3 VM Behavior John Stoffel
2001-06-14 18:25 ` Daniel Phillips
2001-06-14 8:30 ` Mike Galbraith
[not found] <Pine.LNX.4.10.10106140024230.980-100000@coffee.psychology.mcmaster.ca>
2001-06-14 2:08 ` Tom Sightler
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