From: Pavel Machek <pavel@ucw.cz>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Jan Kara <jack@suse.cz>,
Andrew Morton <akpm@linux-foundation.org>,
"Theodore Ts'o" <tytso@mit.edu>,
"Artem S. Tashkinov" <t.artem@lycos.com>,
Wu Fengguang <fengguang.wu@intel.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Mel Gorman <mgorman@suse.de>,
Maxim Patlasov <mpatlasov@parallels.com>
Subject: Re: Disabling in-memory write cache for x86-64 in Linux II
Date: Mon, 4 Nov 2013 13:26:13 +0100 [thread overview]
Message-ID: <20131104122613.GB24407@amd.pavel.ucw.cz> (raw)
In-Reply-To: <CA+55aFw_jjB687nJKuVdjPM6BicF-+0da-wSYHLBqdx0ZfVrGw@mail.gmail.com>
Hi!
> >> - temp-files may not be written out at all.
> >>
> >> Quite frankly, if you have multi-hundred-megabyte temptiles, you've
> >> got issues
> > Actually people do stuff like this e.g. when generating ISO images before
> > burning them.
>
> Yes, but then the temp-file is long-lived enough that it *will* hit
> the disk anyway. So it's only the "create temporary file and pretty
> much immediately delete it" case that changes behavior (ie compiler
> assembly files etc).
>
> If the temp-file is for something like burning an ISO image, the
> burning part is slow enough that the temp-file will hit the disk
> regardless of when we start writing it.
It will hit the disk, but with proposed change, burning still will be
slower.
Before:
create 700MB iso
burn the CD, at the same time writing the iso to disk
After:
create 700MB iso and write most of it to disk
burn the CD, writing the rest.
But yes, limiting dirty ammounts is good idea.
> That said, I'd certainly like it even *more* if the limits really were
> per-BDI, and the global limit was in addition to the per-bdi ones.
> Because when you have a USB device that gets maybe 10MB/s on
> contiguous writes, and 100kB/s on random 4k writes, I think it would
> make more sense to make the "start writeout" limits be 1MB/2MB, not
Actually I believe I seen 10kB/sec on an SD card... would expect that
from USB sticks, too.
And yes, there are actually real problems with this at least on N900.
You do apt-get install <big package>. apt internally does fsyncs. It
results in big enough latencies that watchdogs kick in and kill the
machine.
http://pavelmachek.livejournal.com/117089.html
People are doing
echo 3 > /proc/sys/vm/dirty_ratio
echo 3 > /proc/sys/vm/dirty_background_ratio
echo 100 > /proc/sys/vm/dirty_writeback_centisecs
echo 100 > /proc/sys/vm/dirty_expire_centisecs
echo 4096 > /proc/sys/vm/min_free_kbytes
echo 50 > /proc/sys/vm/swappiness
echo 200 > /proc/sys/vm/vfs_cache_pressure
echo 8 > /proc/sys/vm/page-cluster
echo 4 > /sys/block/mmcblk0/queue/nr_requests
echo 4 > /sys/block/mmcblk1/queue/nr_requests
.. to avoid it, but IIRC it only makes the watchdog reset less likely
:-(.
Pavel
--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
next prev parent reply other threads:[~2013-11-04 12:26 UTC|newest]
Thread overview: 56+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-10-25 7:25 Disabling in-memory write cache for x86-64 in Linux II Artem S. Tashkinov
2013-10-25 8:18 ` Linus Torvalds
2013-10-25 8:30 ` Artem S. Tashkinov
2013-10-25 8:43 ` Linus Torvalds
2013-10-25 9:15 ` Karl Kiniger
2013-10-29 20:30 ` Jan Kara
2013-10-29 20:43 ` Andrew Morton
2013-10-29 21:30 ` Jan Kara
2013-10-29 21:36 ` Linus Torvalds
2013-10-31 14:26 ` Karl Kiniger
2013-11-01 14:25 ` Maxim Patlasov
2013-11-01 14:31 ` [PATCH] mm: add strictlimit knob Maxim Patlasov
2013-11-04 22:01 ` Andrew Morton
2013-11-06 14:30 ` Maxim Patlasov
2013-11-06 15:05 ` [PATCH] mm: add strictlimit knob -v2 Maxim Patlasov
2013-11-07 12:26 ` Henrique de Moraes Holschuh
2013-11-22 23:45 ` Andrew Morton
2013-10-25 11:28 ` Disabling in-memory write cache for x86-64 in Linux II David Lang
2013-10-25 9:18 ` Theodore Ts'o
2013-10-25 9:29 ` Andrew Morton
2013-10-25 9:32 ` Linus Torvalds
2013-10-26 11:32 ` Pavel Machek
2013-10-26 20:03 ` Linus Torvalds
2013-10-29 20:57 ` Jan Kara
2013-10-29 21:33 ` Linus Torvalds
2013-10-29 22:13 ` Jan Kara
2013-10-29 22:42 ` Linus Torvalds
2013-11-01 17:22 ` Fengguang Wu
2013-11-04 12:19 ` Pavel Machek
2013-11-04 12:26 ` Pavel Machek [this message]
2013-10-30 12:01 ` Mel Gorman
2013-11-19 17:17 ` Rob Landley
2013-11-20 20:52 ` One Thousand Gnomes
2013-10-25 22:37 ` Fengguang Wu
2013-10-25 23:05 ` Fengguang Wu
2013-10-25 23:37 ` Theodore Ts'o
2013-10-29 20:40 ` Jan Kara
2013-10-30 10:07 ` Artem S. Tashkinov
2013-10-30 15:12 ` Jan Kara
2013-11-05 0:50 ` Andreas Dilger
2013-11-05 4:12 ` Dave Chinner
2013-11-07 13:48 ` Jan Kara
2013-11-11 3:22 ` Dave Chinner
2013-11-11 19:31 ` Jan Kara
2013-10-25 10:49 ` NeilBrown
2013-10-25 11:26 ` David Lang
2013-10-25 18:26 ` Artem S. Tashkinov
2013-10-25 19:40 ` Diego Calleja
2013-10-25 23:32 ` Fengguang Wu
2013-11-15 15:48 ` Diego Calleja
2013-10-25 20:43 ` NeilBrown
2013-10-25 21:03 ` Artem S. Tashkinov
2013-10-25 22:11 ` NeilBrown
[not found] ` <CAF7GXvpJVLYDS5NfH-NVuN9bOJjAS5c1MQqSTjoiVBHJt6bWcw@mail.gmail.com>
2013-11-05 1:47 ` David Lang
2013-11-05 2:08 ` NeilBrown
2013-10-29 20:49 ` Jan Kara
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