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Re: xfssyncd syncing every five seconds?

To: Nathan Scott <nathans@xxxxxxx>
Subject: Re: xfssyncd syncing every five seconds?
From: Jeremy Field <jezza@xxxxxxxxx>
Date: Thu, 18 Sep 2003 12:53:01 +1000
Cc: linux-xfs@xxxxxxxxxxx
In-reply-to: <20030918122113.A6939@xxxxxxxxxxxxxxxxxxxxxxxx>
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Thanks for your exceedingly rapid reply...

>> I am using linux 2.4.21 with xfs 1.3 on debian-unstable. Since I
>> upgraded from 2.4.18-xfs-1.1, my xfs partitions have been showing
>> pulses of activity every five seconds, I think because of xfssyncd.
>> The hard drive physically seeks every five seconds too.
>> 
>> I have reviewed this mailing list and elsewhere for clues, but can't
>> work out either:
>>      a) whether this behaviour is normal, or
>>      b) how to change the interval.
> 
> A sysctl variable controls this: /proc/sys/fs/xfs/sync_interval

Ok I hadn't realised that's where it lived. Mine's set to "3000". Does
this value rule out the diagnosis I've made?

> >>From Documentation/filesystems/xfs.txt...
> 
>   fs.xfs.sync_interval          (Min: HZ  Default: 30*HZ  Max: 60*HZ)
>         The interval at which the xfssyncd thread for xfs filesystems
>         flushes metadata out to disk. This thread will flush log
>         activity out, and do some processing on unlinked inodes
> 
> What makes you suspect xfssyncd?  It could also be some arbitrary
> process deciding to write something out every few seconds of course.

The reason I suspect xfssyncd is because it happens simultaneously on
all of one drive's xfs partitions together (ie /{,usr,var,home}), and
not on its non-xfs partitions. Additionally, this behaviour is new since
I upgraded to xfs 1.3.

It doesn't actually seem to be happening on another drive which has a
mounted xfs partition. Some other possibly relevant settings:

    $ cat /proc/sys/vm/bdflush 
    30      500     0       0       500     3000    60      20      0
                                    ^ interval in 1/100s between kupdate
                                    flushes -- could this be my problem?
    $ cat /proc/sys/vm/kswapd 
    512     32      8

I guess I feel a bit out of my depth...

Jeremy


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