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Date:      Fri, 20 Aug 2021 18:24:14 +0000
From:      bugzilla-noreply@freebsd.org
To:        bugs@FreeBSD.org
Subject:   [Bug 257318] uma consumes memory when reattaching device
Message-ID:  <bug-257318-227-migiBLUKNY@https.bugs.freebsd.org/bugzilla/>
In-Reply-To: <bug-257318-227@https.bugs.freebsd.org/bugzilla/>
References:  <bug-257318-227@https.bugs.freebsd.org/bugzilla/>

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D257318

--- 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=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20
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 m=
ore
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 t=
here
is a continuous slow leak of additional pages allocated at the UMA level.

I'm not sure there's anything particularly special about mounting/unmountin=
g,
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
problem.

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