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Subject: Re: kmem_map auto-sizing and size dependencies
From: Artem Belevich <art@freebsd.org>
To: Pawel Jakub Dawidek <pjd@freebsd.org>
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Cc: Matthew Fleming <mdf@freebsd.org>,
 FreeBSD Current <freebsd-current@freebsd.org>,
 Andre Oppermann <andre@freebsd.org>,
 freebsd-hackers <freebsd-hackers@freebsd.org>
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On Mon, Jan 21, 2013 at 1:06 PM, Pawel Jakub Dawidek <pjd@freebsd.org> wrote:
> On Fri, Jan 18, 2013 at 08:26:04AM -0800, mdf@FreeBSD.org wrote:
>> >  Should it be set to a larger initial value based on min(physical,KVM) space
>> >  available?
>>
>> It needs to be smaller than the physical space, [...]
>
> Or larger, as the address space can get fragmented and you might not be
> able to allocate memory even if you have physical pages available.

+1 for relaxing upper limit.

I routinely patch all my systems that use ZFS to allow kmem_map size
to be larger than physical memory. Otherwise on a system where most of
RAM goes towards ZFS ARC I used to eventually run into dreaded
kmem_map too small panic.

--Artem