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

From: Baolin Wang
Date: Wed Mar 06 2024 - 04:10:03 EST




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.