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RE: Writeback Stalls

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: RE: Writeback Stalls
From: Markus Stockhausen <stockhausen@xxxxxxxxxxx>
Date: Thu, 20 Sep 2012 04:33:09 +0000
Accept-language: de-DE, en-US
Cc: "xfs@xxxxxxxxxxx" <xfs@xxxxxxxxxxx>
In-reply-to: <20120919213427.GD31501@dastard>
References: <12EF8D94C6F8734FB2FF37B9FBEDD1735831B7A3@xxxxxxxxxxxxxxxxxxxx>,<20120919213427.GD31501@dastard>
Thread-index: Ac2Wj1HT6pr2HR9YR5m1/8HFWskN8gADnaUAABKdJM0=
Thread-topic: Writeback Stalls
> Fundamentally, you are doing it all wrong. High throughput, low
> latency NFS servers write dirty data to disk fast, not leave it
> memory until you run out of clean memory because that causes
> everything to block waiting for writeback IO completion to be ale to
> free memory...

Maybe I did not make it clear enough. The above setup is only
for demonstration purposes. To expose the problem better. In
real life we can see stalls tat thange from 0.5-1 seconds. Even
with all caches active, small dirty writeback settings and unlimited
bandwidth.

In between I found others complaining about the same problem:

http://lwn.net/Articles/486313/
http://oss.sgi.com/archives/xfs/2011-09/msg00189.html

So just one last question: Can I savely revert the the mentioned 
commit d76ee18a8551e33ad7dbd55cac38bc7b094f3abb if I only 
write data to a battery backed up hardware raid controller on a 
server that is attached to an UPS?

Thanks in advance.

Markus

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