On 03/14, Eric W. Biederman wrote: > Pavel Emelianov <xemul@xxxxx> writes: > > > Hi. > > > > I'm looking at how alloc_pid() works and can't understand > > one (simple/stupid) thing. > > > > It first kmem_cache_alloc()-s a strct pid, then calls > > alloc_pidmap() and at the end it taks a global pidmap_lock() > > to add new pid to hash. We need some global lock. pidmap_lock is already here, and it is only used to protect pidmap->page allocation. Iow, it is almost unused. So it was very natural to re-use it while implementing pidrefs. > > The question is - why does alloc_pidmap() use at least > > two atomic ops and potentially loop to find a zero bit > > in pidmap? Why not call alloc_pidmap() under pidmap_lock > > and find zero pid in pidmap w/o any loops and atomics? Currently we search for zero bit lockless, why do you want to do it under spin_lock ? Oleg. _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxx https://lists.osdl.org/mailman/listinfo/containers
