[Bug 257318] uma consumes memory when reattaching device

From: <bugzilla-noreply_at_freebsd.org>
Date: Fri, 20 Aug 2021 18:24:14 UTC

--- Comment #1 from jcaplan@blackberry.com ---
Just to add a bit more detail.

A single iteration might look like this:

# sysctl vm.uma_kmem_total
vm.uma_kmem_total: 26247168
#devctl attach pci0:3:0:0
#devctl detach pci0:3:0:0
# sysctl vm.uma_kmem_total                 
vm.uma_kmem_total: 26251264

Comparing the output before and after for vmstat -m shows that there is no
change in dynamic memory allocated from malloc().

However we see from vm.uma_kmem_total that the UMA is gradually consuming more
memory, and a diff of vmstat -z shows several changes in zone allocations at
the UMA layer.

It appears that all allocations are accounted for at the malloc level yet there
is a continuous slow leak of additional pages allocated at the UMA level.

I'm not sure there's anything particularly special about mounting/unmounting,
it's just an obviously reversible operation that allocates and then frees a lot
of memory. So it's possible this is a specific instance of a more general

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