Bug 257318 - uma consumes memory when reattaching device
Summary: uma consumes memory when reattaching device
Status: New
Alias: None
Product: Base System
Classification: Unclassified
Component: kern (show other bugs)
Version: 13.0-STABLE
Hardware: Any Any
: --- Affects Some People
Assignee: freebsd-bugs (Nobody)
Depends on:
Reported: 2021-07-21 19:25 UTC by jcaplan
Modified: 2022-01-18 19:29 UTC (History)
1 user (show)

See Also:


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Description jcaplan 2021-07-21 19:25:30 UTC

After patching in fixes for all identified leaks, detaching and re-attaching the same device consistently results in kmem allocation.

currently open leaks:

Steps to Reproduce:


for i in {1..1000}; do
        echo $i
        devctl detach pci0:3:0:0
        devctl attach pci0:3:0:0
        sysctl vm.uma_kmem_total

Expected Result

Perhaps after some initial warming stage, detaching and re-attaching the same device should not increase the amount of memory consumed by uma.

Actual Result

Even after many thousands of iterations, uma_kmem_total continues to increase

Build Date & Hardware
FreeBSD freebsd 13.0-RELEASE FreeBSD 13.0-RELEASE #7 releng/13.0-n244733-ea31abc261f-dirty: Wed Jul 21 14:53:10 UTC 2021

Additional Information

Seem to keep hitting keg_alloc_slab from cache_alloc_retry
Comment 1 jcaplan 2021-08-20 18:24:14 UTC
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 problem.