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"cannot set up guest memory" b/c no automatic clearing of Linux' cache
Version: qemu-2.6.0-1
Kernel: 4.4.13-1-MANJARO
Full script (shouldn't matter though): https://pastebin.com/Hp24PWNE
Problem:
When host has been up and used for a while cache has been filled as much that guest can't be started without droping caches.
Expected behavior:
Qemu should be able to request as much Memory as it needs and cause Linux to drop cache pages if needed. A user shouldn't be required to have to come to this conclusion and having to drop caches to start Qemu with the required amount of memory.
My fix:
Following command (as root) required before qemu start:
# sync && echo 3 > /proc/sys/vm/drop_caches
Example:
$ sudo qemu.sh -m 10240 && echo success || echo failed
qemu-system-x86_64: cannot set up guest memory 'pc.ram': Cannot allocate memory
failed
$ free
total used free shared buff/cache available
Mem: 16379476 9126884 3462688 148480 3789904 5123572
Swap: 0 0 0
$ sudo sh -c 'sync && echo 3 > /proc/sys/vm/drop_caches'
$ free
total used free shared buff/cache available
Mem: 16379476 1694528 14106552 149772 578396 14256428
Swap: 0 0 0
$ sudo qemu.sh -m 10240 && echo success || echo failed
success
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