Re: [PATCH 2/3] mm: hugetlb: make the hugetlb migration strategy consistent

[Baolin Wang]

On 2024/3/6 16:46, Oscar Salvador wrote:
> On Wed, Mar 06, 2024 at 04:35:26PM +0800, Baolin Wang wrote:
> > On 2024/2/28 16:41, Oscar Salvador wrote:
>
> > >    	if (folio_test_hugetlb(src)) {
> > >    		struct hstate *h = folio_hstate(src);
> > > +		bool allow_fallback = false;
> > > +
> > > +		if ((1UL << reason) & HTLB_ALLOW_FALLBACK)
> > > +			allow_fallback = true;
> >
> > IMHO, users also should not be aware of these hugetlb logics.
>
> Note that what I wrote there was ugly, because it was just a PoC.
>
> It could be a helper e.g:
>
>   if (hugetlb_reason_allow_alloc_fallback(reason)) (or whatever)
>       allow_fallback_alloc = true
>
> > >    		gfp_mask = htlb_modify_alloc_mask(h, gfp_mask);
> > >    		return alloc_hugetlb_folio_nodemask(h, nid,
> > > -						mtc->nmask, gfp_mask);
> > > +						mtc->nmask, gfp_mask,
> > > +						allow_fallback);
> >
> > 'allow_fallback' can be confusing, that means it is 'allow_fallback' for a
> > new temporary hugetlb allocation, but not 'allow_fallback' for an available
> > hugetlb allocation in alloc_hugetlb_folio_nodemask().
>
> Well, you can pick "alloc_fallback_on_alloc" which is more descriptive I
> guess.

Seems better.

> Bottomline line is that I do not think that choosing to allow
> fallbacking or not here is spreading more logic than having the
> htlb_modify_alloc_mask() here and not directly in
> alloc_hugetlb_folio_nodemask().
>
> As I said, code-wise looks fine, it is just that having to pass
> the 'reason' all the way down and making the decision there makes
> me go "meh..".

Well, fair enough:) let me respin it. Thanks.