netdev - Re: [PATCH net-next 2/4] net: dsa: Link aggregation support

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Message-ID: <5e2d23da-7107-e45e-0ab3-72269d7b6b24@gmail.com>
Date:   Thu, 19 Nov 2020 18:43:38 -0800
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Andrew Lunn <andrew@...n.ch>,
        Tobias Waldekranz <tobias@...dekranz.com>
Cc:     davem@...emloft.net, kuba@...nel.org, vivien.didelot@...il.com,
        olteanv@...il.com, j.vosburgh@...il.com, vfalico@...il.com,
        andy@...yhouse.net, netdev@...r.kernel.org
Subject: Re: [PATCH net-next 2/4] net: dsa: Link aggregation support



On 11/19/2020 4:30 PM, Andrew Lunn wrote:
>> +static struct dsa_lag *dsa_lag_get(struct dsa_switch_tree *dst,
>> +				   struct net_device *dev)
>> +{
>> +	unsigned long busy = 0;
>> +	struct dsa_lag *lag;
>> +	int id;
>> +
>> +	list_for_each_entry(lag, &dst->lags, list) {
>> +		set_bit(lag->id, &busy);
>> +
>> +		if (lag->dev == dev) {
>> +			kref_get(&lag->refcount);
>> +			return lag;
>> +		}
>> +	}
>> +
>> +	id = find_first_zero_bit(&busy, BITS_PER_LONG);
>> +	if (id >= BITS_PER_LONG)
>> +		return ERR_PTR(-ENOSPC);
>> +
>> +	lag = kzalloc(sizeof(*lag), GFP_KERNEL);
>> +	if (!lag)
>> +		return ERR_PTR(-ENOMEM);
> 
> Hi Tobias
> 
> My comment last time was to statically allocated them at probe
> time. Worse case scenario is each port is alone in a LAG. Pointless,
> but somebody could configure it. In dsa_tree_setup_switches() you can
> count the number of ports and then allocate an array, or while setting
> up a port, add one more lag to the list of lags.

The allocation is allowed to sleep (have not checked the calling context
of dsa_lag_get() whether this is OK) so what would be the upside of
doing upfront dsa_lag allocation which could be wasteful?
-- 
Florian