Re: vmem(9) (was Re: netbsd-6: pagedaemon freeze when low on memory)

[Lars Heidieker <lars%heidieker.de@localhost>]

On 2013-03-19 17:40, Richard Hansen wrote:
> On 2013-03-19 06:00, Lars Heidieker wrote:
>> On 2013-03-19 02:11, Greg Troxel wrote:
>>> How hard do you think it would be to make pool_drain() keep trying pools
>>> until one succeeded in freeing something (or it tried them all)?  Do you
>>> see any downside in that change?  It seems like it's just as well to
>>> more aggressively try to free memory when we are out.  If a pool frees
>>> something, it will stop, so it's only when pools do not give back any
>>> space that it will take longer.   The round-robin nature seems to be
>>> built in.  It seems perhaps tricky to retain the round-robin nature and
>>> allow a full cycle; it's not obvious to me that just remembering the
>>> current next pointer is ok, but I think it is.
>>
>> This is an option and looks better to me, a slight downside is we will
>> get more aggressive on pool draining in the normal case (non kva
>> shortage but physical ram) we used to drain one pool in a roundrobin way
>> with the change we drain until we actually drain something so we will
>> trade slightly higher cpu overhead for less unsued memory when there are
>> a lot not drainable pools around which is likely in such situations.
>> Well one could see this as an advantage as well.
>> (there is a timeout in the pool for empty items, so no "ping pong")
>>
>> The question that remains is should we seperate those two cases,
> 
> I don't quite understand what do you mean by "those two cases".  Do you
> mean (1) low on physical RAM (but not KVA), and (2) low on KVA (but not
> physical RAM)?
> 

exactly mesures to take might need to be different, for low on physical
RAM we can start pageouts or free resources as for low on KVA we need to
free resources to free some KVA.


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