On 2026-02-28 03:36:24 [+0000], Jiayuan Chen wrote: > > My only concern is that this will waste a percpu u32 per bond > > device for the majority of bonding use cases (which use modes other than > > balance-rr), which could be a few hundred bytes on a large machine. > > > > Does everything work reliably if the rr_tx_counter allocation > > happens conditionally on mode == BOND_MODE_ROUNDROBIN in bond_setup, as > > well as in bond_option_mode_set? … > An alternative would be to allocate conditionally in bond_init() (since the > default mode is round-robin) > and manage allocation/deallocation in bond_option_mode_set() when the mode > changes.
This sounds reasonable. > This is a trade-off between the added complexity of conditional alloc/free > across multiple code > paths and saving a per-CPU u32 for non-round-robin bonds. > > For the per-CPU u32 overhead, it's only 4 extra bytes per CPU per bond device > — and machines with > that many CPUs tend to have plenty of memory to match. 4 bytes is the minimum allocation for per-CPU memory. The memory is already "there" it is just not assigned. So for the 4 byte allocation it is needed to find a single area (the smallest allocation size). In case there no free block, a new block will be allocated and mapped for each CPU which the part that costs memory. That said, we should not waste memory but it is not _that_ expensive either for a bond device. Things change if here are hundreds of devices. > Thanks > > > -J Sebastian
