kmem leak in tmpmfs?

Fabian Keil freebsd-listen at
Fri May 26 04:15:13 PDT 2006

Iasen Kostov <tbyte at> wrote:

> On Thu, 2006-05-25 at 16:54 -0400, Kris Kennaway wrote:
> > On Thu, May 25, 2006 at 06:01:30PM +0200, Arno J. Klaassen wrote:

> > > I get a very easy to reproduce panic on 6.1-STABLE :
> > > 
> > > /etc/periodic/weekly/310.locate panics with
> > > 
> > >   panic: kmem_malloc(4096): kmem_map too small: 335544320 total
> > > allocated
> > 
> > It looks like you are using a malloc-backed md and you do not have
> > enough RAM to handle the size.  Perhaps tmpmfs does not use swap
> > backing, as it is supposed to?

> 	First of all if there is not enough kmem (not just plain ram
> I think) kernel should not allow disk creation in first place, second
> - I think (although there could be some ... reason for that) it's
> stupid way to say "I don't have more kmem" by panicing :). Better way
> will be just to fail disk operation of that FS with "Disk is full" or
> something like that. At home I tried to raise kmem like that:
> "vm.kmem_size_max="1073741824" (I got 2G of RAM)
> (setting vm.kmem_size directly panices kernel at boot if I remember
> correctly).
> but for my surprise kernel panices at exact same allocated md disk
> space with the same panic as the original poster's. Is it possible
> that I should rise KVA_PAGES too ? And I don't think its documented
> anywhere (of course I've tried googling and it's always possible that
> I've missed something :). All this was on FreeBSD 6.0.

man mdconfig mentions the problem:

             malloc   Storage for this type of memory disk is allocated with
                      malloc(9).  This limits the size to the malloc bucket
                      limit in the kernel.  If the -o reserve option is not
                      set, creating and filling a large malloc-backed memory
                      disk is a very easy way to panic a system.

Use a swap backed disk and the problem will disappear.

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