Public bug reported:
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
** Affects: qemu
Importance: Undecided
Status: New
** Tags: cache memory pc.ram ram
** Summary changed:
- "cannot set up guest memory" and can't clear Linux' Cache
+ "cannot set up guest memory" b/c no automatic clearing of Linux' cache
--
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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:
New
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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