Suggest changing dirhash defaults for FreeBSD 9.2.

[Robert_Burmeister]

Ivan Voras-7 wrote
> On 28/08/2013 05:58, Robert Burmeister wrote:
>> 
>> On 8/27/2013 9:40 AM, Sergey Kandaurov wrote:
>>> On 27 August 2013 16:41, Robert Burmeister
>>> <

> Robert.Burmeister@

> >  wrote:
>>>> I believe that increasing the following values by 10 would benefit
>>>> most FreeBSD users without disadvantage.
>>>> vfs.ufs.dirhash_maxmem: 2097152 to 20971520
>>>> vfs.ufs.dirhash_reclaimage: 5 to 50 or 60
> 
> I'll bump vfs.ufs.dirhash_reclaimage to 60, it's worth it.

Note that vfs.ufs.dirhash_reclaimage is not used to shield ufs_dirhashmem
entries,
rather all entries older than reclaimage are evicted from the cache on
vm_lowmem
before evicting a percentage of the oldest remaining entries.

If it has been hours since a kernel vm_lowmem event,
most of the entries in the cache can be lost due to a momentary memory
spike.

Also note, under kernel memory pressure continuous vm_lowmem events
will effectively extinguish the ufs_dirhash cache, returning its memory to
the kernel.

I believe this prevents the ufsdirhash cache from in any way contributing to
a kernel panic,
so bumping vfs.ufs.dirhash_reclaimage to 60 should be riskless.




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