i915kms: leaks wired memory

[dinoex]

My desktop computer has 16 GiB RAM, but it seems that drm-fbsd12.0-kmod keeps leaking memory, using up all memory in one day and forcing me to reboot.

This computer uses Intel i5-6200U CPU and its integrated Intel Skylake graphics.
The operating system is FreeBSD 12.1.

The version of drm-fbsd12.0-kmod is 4.16.g20200221.

When the system was just booted, wired memory was below 1 GiB.

top:
Mem: 3049M Active, 393M Inact, 174M Laundry, 981M Wired, 497M Buf, 11G Free
Swap: 16G Total, 16G Free

After the system had run for a few hours, wired memory became 14 GiB.
The desktop was still responsive, but the usage of swap was increasing.

After the system had run longer, wired memory become 16 GiB.
The desktop was non-responsive, even shell commands are frozen for 40 secs.

"vmstat -z" keeps stable:
1,392,114,304 TOTAL 1,333,297,844 58,816,460

Unsing the 2nd version of alloctrace.d in issues/155

normal load:
alloctrace.3.log

running mplayer:
alloctrace.4.log