Freebsd 8.0 kmem map too small

[Artem Belevich]

> Thanks for confirmation, I also suspected that. I'll turn using UMA for
> zio allocations off.

Perhaps on i386 only? memory fragmentation is only of concern if you
don't have enough VM space. on amd64 it's easily solved by bumping
vm.kmem_size up -- something that one's typically advised to do
anyways.

If I understand it correctly, without ZIO_USE_UMA, ZFS ARC allocations
would normally be served from power-of-two zones. For relatively
random allocations it would result in  fair amount of waste for
smaller sized allocations.

The increase in apparent amount of wired memory is a bit of red
herring. If ARC size is limited to below wired max and there's enough
physical memory, then UMA caches may keep a lot of memory hanging on
caches' free lists. That memory will be given up as soon as pagedaemon
bothers to wake up.

--Artem



On Tue, May 11, 2010 at 8:29 AM, Pawel Jakub Dawidek <pjd at freebsd.org> wrote:
> On Tue, May 11, 2010 at 04:43:59PM +0300, Alexander V. Ribchansky wrote:
>> As Artem advised, I comment out
>>
>> CFLAGS+=-DZIO_USE_UMA in sys/modules/zfs/Makefile
>>
>> and things like to be "back in USSR :)" if seriously - all become as good
>> as before 18.04.2010 mega ZFS-MFC.
>> While with UMA, Wired memory constantly grow up to kmem_max limit and than
>> PANIC! :(, without it, Wired is approx 380 - 450M on typical 8-STABLE KDE3
>> desktop with plain ZFS.
>> So or there is something wrong with my (and many many other's people's)
>> hands or UMA broke ZFS at all.
>>
>> Thank you, Artem for hint! I already start to think, that revert to
>> pre-18.04.2010 8-STABLE is the only solution.
>
> Thanks for confirmation, I also suspected that. I'll turn using UMA for
> zio allocations off.
>
> --
> Pawel Jakub Dawidek                       http://www.wheelsystems.com
> pjd at FreeBSD.org                           http://www.FreeBSD.org
> FreeBSD committer                         Am I Evil? Yes, I Am!
>