Hi, Peter, On Mon, 2010-11-29 at 20:11 +0800, Peter Zijlstra wrote: > On Mon, 2010-11-29 at 15:03 +0800, Huang Ying wrote: > > This version of the gen_pool memory 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. For > > better scalability, one gen_pool 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. > > > > The basic atomic operation of this allocator is cmpxchg on long. On > > architectures that don't have NMI-safe cmpxchg implementation, a > > spin_trylock_irqsave based fallback is used for gen_pool_alloc, so it > > can be used in NMI handler safely. But gen_pool_free can not be used > > in NMI handler in these architectures, because memory free can not > > fail. > > I still don't see a reason to merge this. > > It makes the genalloc thing slower for every other user (more LOCK'ed > ops) and there is no new user presented in this series. As far as I know, all genalloc users are not performance sensitive. After all, it is mainly used to manage some device memory before. As for users, I think this is a "chicken and egg" problem. And I have plan to use it in APEI code. 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
