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Date:      Thu, 27 Nov 2008 13:11:03 +0200
From:      Nikolay Denev <ndenev@gmail.com>
To:        Pawel Jakub Dawidek <pjd@FreeBSD.org>
Cc:        freebsd-current@freebsd.org
Subject:   Re: HEADS UP: New ZFS in the tree.
Message-ID:  <6F0A14C8-785A-4794-93A5-C3C2770FC231@gmail.com>
In-Reply-To: <64C828D5-3F3C-4AB8-9D12-4EAD30B11818@gmail.com>
References:  <20081117205526.GC1733@garage.freebsd.pl> <8ECD400F-BFE3-4E31-94F0-39AF5F44FDAC@gmail.com> <20081119090307.GA81236@icarus.home.lan> <alpine.BSF.2.00.0811190323110.59299@borg> <FD98E80A-30DC-4700-9C0F-0D77835DBB32@gmail.com> <18E318DD-29FA-4E26-89CF-11B893B42E34@gmail.com> <20081121162518.GC6509@garage.freebsd.pl> <20081122230554.GC2016@garage.freebsd.pl> <8517A9FD-6420-413A-9190-10F3969DEF95@gmail.com> <976654BF-F7A0-41F9-8ECD-8CF76D97EEE9@gmail.com> <64C828D5-3F3C-4AB8-9D12-4EAD30B11818@gmail.com>

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Hi Pawel,

  I don't know if this is going to be helpful, but I did the following  
experiment :

  I've disabled all tuning in loader.conf, all values for arc_max,  
kmem_size and kmem_size_max are
  the defaults computed for amd64 machine with 4G of RAM.
  I've put debug printf()'s in the loop in vm/vm_kern.c:kern_malloc()  
printing the number of loops.
  I've increased the loop count in kern_malloc() from 8 to 100.
  I've also put debug printf()'s in the arc_lowmem() function in zfs's  
ARC cache,
  this should be the function that is called when the "vm_lowmem"  
event fires.

  Then I started one bonnie++ process and watched /var/log/messages.
  Several times the loopcount in kern_malloc() jumped from 0 to 2 or 3  
maximum, and everything
  continued to work, but after 20-30 minutes they started to increase  
steadily and it took
  the machine another maybe 20 minutes to reach 99 loops and then  
panic again with kmem_map too small.

  I hope this makes sense.

- --
Regards,
Nikolay Denev




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