Hi, Andi, Sorry for late. In traveling recently. On Wed, 2010-10-27 at 02:17 -0700, Andi Kleen wrote: > > --- a/lib/genalloc.c > > +++ b/lib/genalloc.c > > @@ -1,8 +1,8 @@ > > /* > > - * Basic general purpose allocator for managing special purpose memory > > - * not managed by the regular kmalloc/kfree interface. > > - * Uses for this includes on-device special memory, uncached memory > > - * etc. > > + * Basic general purpose allocator for managing special purpose > > + * memory, for example, memory that is not managed by the regular > > + * kmalloc/kfree interface. Uses for this includes on-device special > > + * memory, uncached memory etc. > > I think we need some more description here about the locklessness: > > How about adding to the comment: > > This version of the allocator supports lockless operation. > > This makes it safe to use in NMI handlers and other special unblockable > contexts that could otherwise deadlock on locks. This is implemented by > using atomic operations and retries on any conflicts. > The disadvantage is that there may be livelocks in extreme cases. Or add something like: To get better scalability, one allocator can be used for each CPU. > The lockless operation only works if there is enough memory > available. If new memory is added to the pool a lock has to > be still taken. So any user relying on locklessness has to ensure > that sufficient memory is preallocated. In fact, because RCU is used between gen_pool_add and gen_pool_alloc/gen_pool_free, the memory can be added to pool at any time. This makes the memory allocator more flexible. Maybe we can add gen_pool_remove in the future to shrink the preallocated memory at any time. > The basic atomic operation of this allocator is cmpxchg on long. > On architectures that don't support cmpxchg natively a fallback > is used. If the fallback uses locks it may not be safe to use > it in NMI contexts on these architectures. > > > +/** > > + * gen_pool_for_each_chunk - iterate over chunks of generic memory pool > > + * @chunk: the struct gen_pool_chunk * to use as a loop cursor > > + * @pool: the generic memory pool > > + */ > > I believe that's not safe in a lockless context right? > Should note that. Yes. Will add that. Best Regards, Huang Ying -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
