kern/187594: [zfs] [patch] ZFS ARC behavior problem and fix

[Karl Denninger]

The following reply was made to PR kern/187594; it has been noted by GNATS.

From: Karl Denninger <karl at denninger.net>
To: bug-followup at FreeBSD.org, karl at fs.denninger.net
Cc:  
Subject: Re: kern/187594: [zfs] [patch] ZFS ARC behavior problem and fix
Date: Thu, 20 Mar 2014 07:26:39 -0500

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 I am increasingly-convinced with increasing runtime now on both=20
 synthetic and real loads in production that the proper default value for =
 
 vfs.zfs.arc_freepages is vm.stats.vm.v_free_target less "just a bit." =20
 Five percent appears to be ok for most workloads with RAM configurations =
 
 ranging from 4GB to the 24GB area (configurations that I can easily test =
 
 under both synthetic and real environments.)
 
 Larger invasions of the free target increasingly risk provocation of the =
 
 behavior that prompted me to get involved in working this part of the=20
 code in the first place, including short-term (~5-10 second) "stalls"=20
 during which the system appears to be locked up, but is not.
 
 It appears that the key to avoiding that behavior is to not allow the=20
 ARC to continue to take RAM when a material invasion of that target=20
 space has occurred.
 
 --=20
 -- Karl
 karl at denninger.net
 
 
 
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