Re: [pve-devel] [PATCH v2 guest-common 1/1] helpers: add pool limit/usage helpers

[Daniel Kral <d.kral@proxmox.com>]

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On 16/04/2024 14:20, Fabian Grünbichler wrote:
> one for combining the per-node broadcasted values, one for checking a pool's
> limit, and one specific helper for checking guest-related actions such as
> starting a VM.
> 
> Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>
> ---
> 
> Notes:
>     v2:
>     - style
>     - introduce new helper for mapping limit key to usage hash
>     - introduce new helper for default usage hash
>     - avoid hard-coding cpu/mem and run/config where sensible
> 
>  src/PVE/GuestHelpers.pm | 183 ++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 183 insertions(+)
> 
> diff --git a/src/PVE/GuestHelpers.pm b/src/PVE/GuestHelpers.pm
> index 961a7b8..e52eaf0 100644
> --- a/src/PVE/GuestHelpers.pm
> +++ b/src/PVE/GuestHelpers.pm
> @@ -416,4 +416,187 @@ sub check_vnet_access {
>  	if !($tag || $trunks);
>  }
>  
> +sub pool_limit_to_usage {
> +    my ($limit_key) = @_;
> +
> +    my ($resource, $kind) = split(/-/, $limit_key, 2);
> +
> +    return ($resource, $kind, $kind eq 'run' ? 1 : 0);
> +}
> +
> +sub pool_default_usage {
> +    my $default = {};
> +
> +    for my $limit (keys $PVE::AccessControl::pool_limits_desc->%*) {

Perlcritic complains here about the direct access to the
`pool_limits_desc`. I haven't found any other occurence where we
reference a variable across packages directly. I can see that they are
only used here, but would it make sense to move these helpers (which are
unrelated to guests themselves) to the `PVE::AccessControl` package?

> +	my ($resource, $kind) = pool_limit_to_usage($limit);
> +	$default->{$resource}->{$kind} = 0;
> +    }
> +
> +    return $default;
> +}
> +
> +# combines the broadcasted pool usage information to get per-pool stats
> +#
> +# $pools parsed pool info from user.cfg
> +# $usage broadcasted KV hash
> +# $pool filter for specific pool
> +# $skip skip a certain guest to ignore its current usage
> +#
> +# returns usage hash:
> +# pool -> cpu/mem/.. -> run/config -> $usage
> +sub get_pool_usage {
> +    my ($pools, $usage, $pool, $skip) = @_;
> +
> +    my $res = {};
> +    my $included_guests = {};
> +    for my $node (keys $usage->%*) {
> +	my $node_usage = JSON::decode_json($usage->{$node} // '');

As pointed out in the pve-manager ui patch, `encode_json` and
`decode_json` seem to be a little racy for preserving the order. If
these values stay user visible, we should sort the keys here afterwards,
so users can rely on some preserved order.

> +
> +	# long IDs first, so we can add children to their parents right away
> +	for my $poolid (sort {$b cmp $a} keys $pools->%*) {
> +	    if (
> +		defined($pool)
> +		&& !($pool eq $poolid || $poolid =~ m!^$pool/! || $pool =~ m!^$poolid/!)
> +	    ) {
> +		next;
> +	    }
> +
> +	    my $d = $res->{$poolid} //= pool_default_usage();
> +
> +	    my $pool_usage = $node_usage->{data}->{$poolid} // {};
> +	    for my $vmid (keys $pool_usage->%*) {
> +		# only include once in case of migration between broadcast
> +		next if $included_guests->{$vmid};
> +		next if $skip && $skip->{$vmid};
> +		$included_guests->{$vmid} = 1;
> +
> +		my $vm_data = $pool_usage->{$vmid};
> +		for my $key (keys $vm_data->%*) {
> +		    next if $key eq 'running';
> +		    $d->{$key}->{run} += $vm_data->{$key}->{run} if $vm_data->{running};
> +		    $d->{$key}->{config} += $vm_data->{$key}->{config};
> +		}
> +	    }
> +
> +	    if (my $parent = $pools->{$poolid}->{parent}) {
> +		$res->{$parent} //= pool_default_usage();
> +		for my $key (keys $d->%*) {
> +		    for my $kind (keys $d->{$key}->%*) {
> +			$res->{$parent}->{$key}->{$kind} = $d->{$key}->{$kind};
> +		    }
> +		}
> +	    }
> +	}
> +    }
> +
> +    return $res;
> +}
> +
> +# checks whether a pool is (or would be) over its resource limits
> +#
> +# $changes is for checking limits for config/state changes like VM starts, if
> +# set, only the limits with changes are checked (see check_guest_pool_limit)
> +#
> +# return value indicates whether any limit was overstepped or not (if $noerr is set)
> +sub check_pool_limits {
> +    my ($usage, $limits, $noerr, $changes) = @_;
> +
> +    my $over = {};
> +    my $only_changed = defined($changes);
> +
> +    my $check_limit = sub {
> +	my ($key, $running, $limit, $change) = @_;
> +
> +	return if $only_changed && $change == 0;
> +
> +	my $kind = $running ? 'run' : 'config';
> +
> +	my $value = $usage->{$key}->{$kind};
> +	$value = int($value);
> +	$value += $change;
> +	$value = $value / (1024*1024) if $key eq 'mem';
> +	if ($limit < $value) {
> +	    $over->{$key}->{$kind}->{change} = $change if $change;
> +	    $over->{$key}->{$kind}->{over} = 1;
> +	}
> +    };
> +
> +    my $get_change = sub {
> +	my ($key, $running) = @_;
> +
> +	return 0 if !defined($changes);
> +
> +	my $check_running = defined($changes->{running}) && $changes->{running} ? 1 : 0;
> +
> +	if ($running == $check_running) {
> +	    return $changes->{$key} // 0;
> +	} else {
> +	    return 0;
> +	}
> +    };
> +
> +    while (my ($key, $limit) = each $limits->%*) {
> +	my ($resource, $kind, $running) = pool_limit_to_usage($key);
> +	my $change = $get_change->($resource, $running);
> +	$check_limit->($resource, $running, $limit, $change);
> +    }
> +
> +    if (!$noerr) {
> +	my $msg = '';
> +	for my $key (keys $over->%*) {
> +	    for my $kind (keys $over->{$key}->%*) {
> +		my $value = $usage->{$key}->{$kind};
> +		$value = $value / (1024*1024) if $key eq 'mem';
> +		my $change = $over->{$key}->{$kind}->{change};
> +		if ($change) {
> +		    $change = $change / (1024*1024) if $key eq 'mem';
> +		    $value = "$value + $change" if $change;
> +		}
> +		my $limit = $limits->{"$key-$kind"};
> +		$msg .= "($kind) $key: $value over $limit, ";
> +	    }
> +	}
> +	if ($msg) {
> +	$msg =~ s/, $//;
> +	die "pool limits exhausted: $msg\n";
> +	}
> +    }
> +
> +    return $over->%* ? 1 : 0;
> +}
> +
> +# checks whether the given changes for a certain guest would overstep a pool limit
> +#
> +# $changes is an optional hash containing
> +# - absolute: flag whether changes are relative or absolute
> +# - running: flag whether the config or running limits should be checked
> +# - cpu: change value for cpu limit
> +# - mem: change value for mem limit

the description could benefit from a unit, i.e. "in bytes".

FWIW, we could use `PVE::Tools::convert_size` more often to make the
input values more agnostic to prefix (e.g. Mega vs Giga) and base unit
(bit vs byte) to reduce the cognitive load across pve-container and
qemu-server when to use what. We could also use that information above
for the error message to include units (i.e. "$value MiB over $limit").
But that would involve much more effort and I'm unsure it's worth it.

> +# all elements are optional
> +#
> +# if no $changes is provided, the limits are checked against the current usage
> +#
> +# $poolid allows overriding the guest's pool membership, for example in case it
> +# is not yet properly set when creating the guest
> +sub check_guest_pool_limit {
> +    my ($vmid, $changes, $poolid) = @_;
> +
> +    my $user_cfg = PVE::Cluster::cfs_read_file("user.cfg");
> +
> +    $poolid = $user_cfg->{vms}->{$vmid} if !defined($poolid);
> +    if ($poolid) {
> +	my $pool = $user_cfg->{pools}->{$poolid};
> +
> +	my $limits = $pool->{limits};
> +	return if !$limits;
> +
> +	my $skip = {};
> +	$skip->{$vmid} = 1 if $changes && $changes->{absolute};
> +	my $usage = PVE::Cluster::get_node_kv('pool-usage');
> +
> +	$usage = get_pool_usage($user_cfg->{pools}, $usage, $poolid, $skip);
> +	check_pool_limits($usage->{$poolid}, $limits, 0, $changes);
> +    }
> +}
> +
>  1;
> -- 
> 2.39.2








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