Re: [PATCH v10 07/13] khugepaged: skip collapsing mTHP to smaller orders

On 21/08/25 5:35 pm, Lorenzo Stoakes wrote:

quoted

---
  mm/khugepaged.c | 9 +++++++++
  1 file changed, 9 insertions(+)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 1ad7e00d3fd6..6a4cf7e4a7cc 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c

@@ -611,6 +611,15 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
  		folio = page_folio(page);
  		VM_BUG_ON_FOLIO(!folio_test_anon(folio), folio);

+		/*
+		 * TODO: In some cases of partially-mapped folios, we'd actually
+		 * want to collapse.
+		 */

Not a fan of adding todo's in code, they have a habit of being left forever. I'd
maybe put a more written  out comment something similar to the commit message.

I had suggested to add in https://lore.kernel.org/all/20250211111326.14295-10-dev.jain@arm.com/ (local)
from the get go, but then we decided to leave it for later. So rest assured this TODO won't
be left forever : )

quoted

+		if (order != HPAGE_PMD_ORDER && folio_order(folio) >= order) {
+			result = SCAN_PTE_MAPPED_HUGEPAGE;
+			goto out;
+		}
+
  		/* See collapse_scan_pmd(). */
  		if (folio_maybe_mapped_shared(folio)) {
  			++shared;
--
2.50.1