svn commit: r242910 - in user/andre/tcp_workqueue/sys: kern sys

[Andre Oppermann]

On 12.11.2012 16:52, Alfred Perlstein wrote:
> If maxusers is set (loader.conf/config(8)) can you please revert to maxusers based limits?

No.  That's way to complicated.

-- 
Andre

> Sent from my iPhone
>
> On Nov 12, 2012, at 2:49 AM, Andre Oppermann <andre at freebsd.org> wrote:
>
>> On 12.11.2012 09:47, Andre Oppermann wrote:
>>> Author: andre
>>> Date: Mon Nov 12 08:47:13 2012
>>> New Revision: 242910
>>> URL: http://svnweb.freebsd.org/changeset/base/242910
>>>
>>> Log:
>>>    Base the mbuf related limits on the available physical memory or
>>>    kernel memory, whichever is lower.
>>
>> The commit message is a bit terse so I'm going to explain in more
>> detail:
>>
>> The overall mbuf related memory limit must be set so that mbufs
>> (and clusters of various sizes) can't exhaust physical RAM or KVM.
>>
>> I've chosen a limit of half the physical RAM or KVM (whichever is
>> lower) as the baseline.  In any normal scenario we want to leave
>> at least half of the physmem/kvm for other kernel functions and
>> userspace to prevent it from swapping like hell.  Via a tunable
>> it can be upped to at most 3/4 of physmem/kvm.
>>
>> Out of the overall mbuf memory limit I've chosen 2K clusters, 4K
>> (page size) clusters to get 1/4 each because these are the most
>> heavily used mbuf sizes.  2K clusters are used for MTU 1500 ethernet
>> inbound packets.  4K clusters are used whenever possible for sends
>> on sockets and thus outbound packets.
>>
>> The larger cluster sizes of 9K and 16K are limited to 1/6 of the
>> overall mbuf memory limit.  Again, when jumbo MTU's are used these
>> large clusters will end up only on the inbound path.  They are not
>> used on outbound, there it's still 4K.  Yes, that will stay that
>> way because otherwise we run into lots of complications in the
>> stack.  And it really isn't a problem, so don't make a scene.
>>
>> Previously the normal mbufs (256B) weren't limited at all.  This
>> is wrong as there are certain places in the kernel that on allocation
>> failure of clusters try to piece together their packet from smaller
>> mbufs.  The mbuf limit is the number of all other mbuf sizes together
>> plus some more to allow for standalone mbufs (ACK for example) and
>> to send off a copy of a cluster.  FYI: Every cluster eventually also
>> has an mbuf associated with it.
>>
>> Unfortunately there isn't a way to set an overall limit for all
>> mbuf memory together as UMA doesn't support such a limiting.
>>
>> Lets work out a few examples on sizing:
>>
>> 1GB KVM:
>> 512MB limit for mbufs
>> 419,430 mbufs
>>   65,536 2K mbuf clusters
>>   32,768 4K mbuf clusters
>>    9,709 9K mbuf clusters
>>    5,461 16K mbuf clusters
>>
>> 16GB RAM:
>> 8GB limit for mbufs
>> 33,554,432 mbufs
>>   1,048,576 2K mbuf clusters
>>     524,288 4K mbuf clusters
>>     155,344 9K mbuf clusters
>>      87,381 16K mbuf clusters
>>
>> These defaults should be sufficient for event the most demanding
>> network loads.  If you do run into these limits you probably know
>> exactly what you are doing and you are expected to tune those
>> values for your particular purpose.
>>
>> There is a side-issue with maxfiles as it relates to the maximum
>> number of sockets that can be opened at the same time.  With web
>> servers and proxy caches of these days there may be some 100K or
>> more sockets open.  Hence I've divorced maxfiles from maxusers as
>> well.  There is a relationship of maxfiles with the callout callwheel
>> though which has to be investigated some more to prevent ridiculous
>> values from being chosen.
>>
>> --
>> Andre
>>
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