[pve-devel] [PATCH qemu-server 0/1] enable balloon free-page-reporting

[pve-devel] [PATCH qemu-server 0/1] enable balloon free-page-reporting

[Alexandre Derumier]

Hi,

Currently, if a guest vm allocate a memory page, and freed it later in the guest,
the memory is not freed on the host side.

Balloon device have a new option since qemu 5.1 "free-page-reporting" (and need host kernel 5.7)

https://events19.linuxfoundation.org/wp-content/uploads/2017/12/KVMForum2018.pdf
https://lwn.net/Articles/759413/

This is working like the discard option for disk, memory is freed async by the host when vm is freeing it.

I'm running it production since 1 month without any problem. With a lot of vms and spiky workload, the memory
freed is really huge.


This patch enabled it by default,

This don't break live migration  from old qemu process with non-enable free page hinting -->  new qemu process with enabled free page hinting,
but this break migration in the reverse way.


So I can enabled it by default for next qemu machine version or add an extra option to enable it.
I don't known if we could extend the "baloon" option ? or add an extra option like "balloonoptions: ..." ?

What do you think about it ?


Alexandre Derumier (1):
  enable balloon free-page-reporting

 PVE/QemuServer.pm | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

-- 
2.30.2

[pve-devel] [PATCH qemu-server 1/1] enable balloon free-page-reporting

[Alexandre Derumier]

Allow balloon device  driver to report hints of guest free pages to the host,
for auto memory reclaim

https://lwn.net/Articles/759413/
https://events19.linuxfoundation.org/wp-content/uploads/2017/12/KVMForum2018.pdf
Signed-off-by: Alexandre Derumier <aderumier@odiso.com>
---
 PVE/QemuServer.pm | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/PVE/QemuServer.pm b/PVE/QemuServer.pm
index 42f0fbd..bb44e58 100644
--- a/PVE/QemuServer.pm
+++ b/PVE/QemuServer.pm
@@ -3846,7 +3846,7 @@ sub config_to_command {
     # enable balloon by default, unless explicitly disabled
     if (!defined($conf->{balloon}) || $conf->{balloon}) {
 	my $pciaddr = print_pci_addr("balloon0", $bridges, $arch, $machine_type);
-	push @$devices, '-device', "virtio-balloon-pci,id=balloon0$pciaddr";
+	push @$devices, '-device', "virtio-balloon-pci,free-page-reporting=on,id=balloon0$pciaddr";
     }
 
     if ($conf->{watchdog}) {
-- 
2.30.2