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

[Barry Song]

On Sat, Aug 17, 2024 at 9:17 AM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote:
>
> 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?
>

had definitely thought about charging order-0 as well in
alloc_swap_folio() when sending this
quick fix mainly for quick verification it can fix the problem. v7
will definitely charge order-0
in alloc_swap_folio().

> > @@ -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.

I suppose this is done by folio_put() automatically.

Thanks
Barry