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Re: High latencies writing to a memory mapped file

To: Shawn Bohrer <shawn.bohrer@xxxxxxxxx>
Subject: Re: High latencies writing to a memory mapped file
From: Matthias Schniedermeyer <ms@xxxxxxx>
Date: Tue, 27 Jul 2010 11:24:52 +0200
Cc: xfs@xxxxxxxxxxx
In-reply-to: <20100722144706.GA2840@xxxxxxxxxxxxxxxxxxxxxxxxx>
References: <20100722144706.GA2840@xxxxxxxxxxxxxxxxxxxxxxxxx>
User-agent: Mutt/1.5.19 (2009-01-05)
On 22.07.2010 09:47, Shawn Bohrer wrote:

I can't help with your exact problem, but this reminds me of a quite 
similar looking problem i have.

We have a linux-computer with samba to act as a fileserver for a few 
Windows-Clients and ever since kernel 2.6.26 (Never happend with 2.6.25) 
the server randomly "hangs" for a few seconds (Which is more of a 
problem that drives people crazy). It takes about 1-2 weeks for the 
symtoms to show and only a reboot of the computer "cures" it (for 
another 1-2 weeks).

Because of the long incubation period and the whole slew of subsystems 
(and samba) involded, i never had the drive to debug this, as a "quick" 
reboot every 1-2 weeks only takes about 2 minutes.

With "whole slew of subsystems" in mean:
Hardware: SATA on onboard-controller (Intel G41-Chipset(ICH7) with 
PIIX-driver, because BIOS is crippled and doesn't allow AHCI)
(Hardware itself is unlikly to be be at fault, because a few month ago 
the complete computer and HDDs were switched, but the problem persisted)

Currently 2.6.32(-5, Debian SID), first seen with 2.6.26 (vanilla)

md(RAID1), loop-aes, XFS
(I tried logbufs=8,logbsize=256k,nobarrier, no apparent changes. I'm 
not 100% sure if i tried other schedulers, but i think i did)

And finally Samba on top.

As i had to reboot the computer just yesterday, and will have to power 
down the server over the weekend because we are moving, it will be at 
least 2-3 weeks before i anticipate the problem to resurface.
In case anybody has an idea what i could do to identify and/or isolate 
the root-cause, i'm open for suggestions.

Bis denn

Real Programmers consider "what you see is what you get" to be just as 
bad a concept in Text Editors as it is in women. No, the Real Programmer
wants a "you asked for it, you got it" text editor -- complicated, 
cryptic, powerful, unforgiving, dangerous.

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