Re: [PATCH v6 2/2] mm: support large folios swap-in for zRAM-like devices

[Matthew Wilcox]

On Fri, Aug 16, 2024 at 11:06:12AM +1200, Barry Song wrote:
> When memcg approaches its limit, charging mTHP becomes difficult.
> At this point, when the charge fails, we fallback to the next order
> to avoid repeatedly retrying larger orders.

Why do you always find the ugliest possible solution to a problem?

> @@ -4244,7 +4248,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
>  				}
>  				need_clear_cache = true;
>  
> -				if (mem_cgroup_swapin_charge_folio(folio,
> +				if (nr_pages == 1 && mem_cgroup_swapin_charge_folio(folio,
>  							vma->vm_mm, GFP_KERNEL,
>  							entry)) {
>  					ret = VM_FAULT_OOM;

Just make alloc_swap_folio() always charge the folio, even for order-0.

And you'll have to uncharge it in the swapcache_prepare() failure case.