[PATCH v5 1/3] mm: hugetlb: Consolidate interpretation of gbl_chg within alloc_hugetlb_folio()

The dequeue_hugetlb_folio_vma() function currently handles the gbl_chg
parameter to determine if a folio can be dequeued based on global page
availability. This leaks reservation-specific logic into the dequeueing
path.

Relocate this logic to alloc_hugetlb_folio() so that
dequeue_hugetlb_folio_vma() focuses solely on selecting and dequeuing a
folio. In alloc_hugetlb_folio(), only attempt to dequeue a folio if a
reservation exists (gbl_chg == 0) or if there are available huge pages in
the global pool.

No functional change intended.

Reviewed-by: James Houghton <[email protected]>
Acked-by: Oscar Salvador <[email protected]>
Reviewed-by: Joshua Hahn <[email protected]>
Signed-off-by: Ackerley Tng <[email protected]>
---
 mm/hugetlb.c | 26 +++++++++++---------------
 1 file changed, 11 insertions(+), 15 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index e93c4d2456aa4..7985cfd21a03c 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1319,7 +1319,7 @@ static unsigned long available_huge_pages(struct hstate *h)
 
 static struct folio *dequeue_hugetlb_folio_vma(struct hstate *h,
 				struct vm_area_struct *vma,
-				unsigned long address, long gbl_chg)
+				unsigned long address)
 {
 	struct folio *folio = NULL;
 	struct mempolicy *mpol;
@@ -1327,13 +1327,6 @@ static struct folio *dequeue_hugetlb_folio_vma(struct hstate *h,
 	nodemask_t *nodemask;
 	int nid;
 
-	/*
-	 * gbl_chg==1 means the allocation requires a new page that was not
-	 * reserved before.  Making sure there's at least one free page.
-	 */
-	if (gbl_chg && !available_huge_pages(h))
-		goto err;
-
 	gfp_mask = htlb_alloc_mask(h);
 	nid = huge_node(vma, address, gfp_mask, &mpol, &nodemask);
 
@@ -1351,9 +1344,6 @@ static struct folio *dequeue_hugetlb_folio_vma(struct hstate *h,
 
 	mpol_cond_put(mpol);
 	return folio;
-
-err:
-	return NULL;
 }
 
 #if defined(CONFIG_ARCH_HAS_GIGANTIC_PAGE) && defined(CONFIG_CONTIG_ALLOC)
@@ -2923,12 +2913,18 @@ struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma,
 		goto out_uncharge_cgroup_reservation;
 
 	spin_lock_irq(&hugetlb_lock);
+
 	/*
-	 * glb_chg is passed to indicate whether or not a page must be taken
-	 * from the global free pool (global change).  gbl_chg == 0 indicates
-	 * a reservation exists for the allocation.
+	 * Try to dequeue from the pool if either:
+	 * 1) A reservation exists (gbl_chg == 0).
+	 * 2) No reservation exists, but there are unreserved (available)
+	 *    pages in the pool; this prefers using pre-allocated pool
+	 *    pages over allocating fresh ones from the buddy allocator.
 	 */
-	folio = dequeue_hugetlb_folio_vma(h, vma, addr, gbl_chg);
+	folio = NULL;
+	if (!gbl_chg || available_huge_pages(h))
+		folio = dequeue_hugetlb_folio_vma(h, vma, addr);
+
 	if (!folio) {
 		spin_unlock_irq(&hugetlb_lock);
 		folio = alloc_buddy_hugetlb_folio_with_mpol(h, vma, addr);

-- 
2.55.0.508.g3f0d502094-goog