ARC size constantly shrinks, then ZFS slows down extremely

Attila Nagy bra at
Mon Oct 12 08:32:29 UTC 2009

K. Macy wrote:
>> The amd64 machine started to loose ARC memory again. See these:
>> Your patch was active between 7 and 9. You can see that the ARC size 
>> was somewhat constant.
>> On october 9, I installed Kip's modification, and ARC size started to 
>> decrease.
>> BTW, previously (before october 7) I set the arc min size to 10-15GB 
>> (can't remember the exact value), but now it runs with the defaults 
>> (only the max size is set):
>> vfs.zfs.arc_min: 3623878656
>> vfs.zfs.arc_max: 28991029248
>> As you can see, there are plenty of memory. This machine uses UFS as 
>> well (and writes it heavily), maybe that's what affects ZFS size, by 
>> caching a lot of stuff?
> Currently, the inactive page queue will grow until ARC is shrunk to 
> arc_min. 
> I think I'll probably spend some time making the ARC play better with 
> the page cache this week. Unfortunately, under heavy memory pressure 
> when competing with UFS the ARC will degrade to LRU, but I think that 
> is still an improvement over the current static sizing with low and 
> high water marks.
Will setting ARC's minimum size help here? (I will try)

For me, it's OK, and I think it's generally not a problem, if somebody 
uses UFS as well.
Is it possible to merge the memory management of the two, or they are 
completely different beasts?


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