Re: [pve-devel] [PATCH qemu-server] fix #2570: add 'keephugepages' config

[Thomas Lamprecht <t.lamprecht@proxmox.com>]

On 12.02.20 14:32, Stefan Reiter wrote:
> We already keep hugepages if they are created with the kernel
> commandline (hugepagesz=x hugepages=y), but some setups (specifically
> hugepages across multiple NUMA nodes) cannot be configured that way.
> Since we always clear these hugepages at VM shutdown, rebooting a VM
> that uses them might not work, since the requested count might not be
> available anymore by the time we want to use them (also, we would then
> no longer allocate them correctly on the NUMA nodes).
> 

but they also will be kept on normal shutdown now.
Why not do this transparent, without extra config, solely on API reboot call?

> Add a 'keephugepages' parameter to skip cleanup and simply leave them
> untouched.
> 
> Signed-off-by: Stefan Reiter <s.reiter@proxmox.com>
> ---
> 
> I tried adding it as a 'keep' sub-parameter first (i.e.
> 'hugepages: 1024,keep=1' etc.), but it turns out that we hardcode
> $config->{hugepages} to be a numeric string in a *lot* of different places, so I
> opted for this variant instead. Open for suggestions ofc.
> 
>  PVE/QemuServer.pm | 14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/PVE/QemuServer.pm b/PVE/QemuServer.pm
> index 23176dd..4741707 100644
> --- a/PVE/QemuServer.pm
> +++ b/PVE/QemuServer.pm
> @@ -384,6 +384,14 @@ EODESC
>  	description => "Enable/disable hugepages memory.",
>  	enum => [qw(any 2 1024)],
>      },
> +    keephugepages => {
> +	optional => 1,
> +	type => 'boolean',
> +	default => 0,
> +	description => "Use together with hugepages. If enabled, hugepages will"
> +		     . " not be deleted after VM shutdown and can be used for"
> +		     . " subsequent starts.",
> +    },
>      vcpus => {
>  	optional => 1,
>  	type => 'integer',
> @@ -5441,11 +5449,13 @@ sub vm_start {
>  
>  		eval { $run_qemu->() };
>  		if (my $err = $@) {
> -		    PVE::QemuServer::Memory::hugepages_reset($hugepages_host_topology);
> +		    PVE::QemuServer::Memory::hugepages_reset($hugepages_host_topology)
> +			if !$conf->{keephugepages};
>  		    die $err;
>  		}
>  
> -		PVE::QemuServer::Memory::hugepages_pre_deallocate($hugepages_topology);
> +		PVE::QemuServer::Memory::hugepages_pre_deallocate($hugepages_topology)
> +		    if !$conf->{keephugepages};
>  	    };
>  	    eval { PVE::QemuServer::Memory::hugepages_update_locked($code); };
>  
>