Quetion about the counter ZCounterOutOfMemory

[Stefan Karlsson]

Hi Guoxiong,

On 2024-03-31 15:54, Guoxiong Li wrote:
> Hi all,
>
> I notice the ZCounterOutOfMemory is only increased in the call link
> `ZAllocatorEden::alloc_object -> ZHeap::out_of_memory`.
> Should we increase this counter in the method 
> `ZAllocatorEden::alloc_tlab`

I don't think we should. When we fail alloc_tlab, the code will continue 
and try a direct allocation with alloc_object. See:

HeapWord* MemAllocator::mem_allocate_slow(Allocation& allocation) const {
   // Allocation of an oop can always invoke a safepoint.
debug_only(allocation._thread->check_for_valid_safepoint_state());

   if (UseTLAB) {
     // Try refilling the TLAB and allocating the object in it.
     HeapWord* mem = mem_allocate_inside_tlab_slow(allocation);
     if (mem != nullptr) {
       return mem;
     }
   }

   return mem_allocate_outside_tlab(allocation);
}

> and other allocation methods such as 
> `ZAllocatorForRelocation::alloc_object`?

Relocations will never fail. If we run out of memory during relocation, 
the object will be in-place compacted into its current ZPage.

> And should we move the incremental code like `ZHeap::out_of_memory` to
> the allocation methods of `ZObjectAllocator`, which is a lower level 
> class for allocation.

If we should do anything here, I think it is to move the call to 
ZHeap::out_of_memory() to ZCollectedHeap::mem_allocate.

Cheers,
StefanK

>
> Any ideas are appreciated. Thanks.
>
> Best Regards,
> -- Guoxiong