Thanks Celmor; that might be one for the zfs guys then if that's what's
holding onto the caches; I suspect their caching is a bit different from
the rest of the Linux filesystems.
I'm going to close this as 'invalid' because I'm pretty sure this isn't
a qemu bug; the kernel should be giving us the RAM we asked for if it's
got it.
** Changed in: qemu
Status: New => Invalid
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https://bugs.launchpad.net/bugs/1609968
Title:
"cannot set up guest memory" b/c no automatic clearing of Linux' cache
Status in QEMU:
Invalid
Bug description:
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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