On Tue, 2021-01-12 at 16:37 +0200, Vladimir Oltean wrote: > On Mon, Jan 11, 2021 at 03:38:49PM -0800, Saeed Mahameed wrote: > > GFP_ATOMIC is a little bit aggressive especially when user daemons > > are > > periodically reading stats. This can be avoided. > > > > You can pre-allocate with GFP_KERNEL an array with an "approximate" > > size. > > then fill the array up with whatever slaves the the bond has at > > that > > moment, num_of_slaves can be less, equal or more than the array > > you > > just allocated but we shouldn't care .. > > > > something like: > > rcu_read_lock() > > nslaves = bond_get_num_slaves(); > > rcu_read_unlock() > > sarray = kcalloc(nslaves, sizeof(struct bonding_slave_dev), > > GFP_KERNEL); > > rcu_read_lock(); > > bond_fill_slaves_array(bond, sarray); // also do: dev_hold() > > rcu_read_unlock(); > > > > > > bond_get_slaves_array_stats(sarray); > > > > bond_put_slaves_array(sarray); > > I don't know what to say about acquiring RCU read lock twice and > traversing the list of interfaces three or four times.
You can optimize this by tracking #num_slaves. > On the other hand, what's the worst that can happen if the GFP_ATOMIC > memory allocation fails. It's not like there is any data loss. > User space will retry when there is less memory pressure. Anyway Up to you, i just don't like it when we use GFP_ATOMIC when it can be avoided, especially for periodic jobs, like stats polling..
