khugepaged: convert alloc_charge_hpage to alloc_charge_folio

Both callers want to deal with a folio, so return a folio from this
function.

Link: https://lkml.kernel.org/r/20240403171838.1445826-3-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/khugepaged.c

@@ -1045,7 +1045,7 @@ static int __collapse_huge_page_swapin(struct mm_struct *mm,
 	return result;
 }
 
-static int alloc_charge_hpage(struct page **hpage, struct mm_struct *mm,
+static int alloc_charge_folio(struct folio **foliop, struct mm_struct *mm,
 			      struct collapse_control *cc)
 {
 	gfp_t gfp = (cc->is_khugepaged ? alloc_hugepage_khugepaged_gfpmask() :
@@ -1055,7 +1055,7 @@ static int alloc_charge_hpage(struct page **hpage, struct mm_struct *mm,
 
 	folio = __folio_alloc(gfp, HPAGE_PMD_ORDER, node, &cc->alloc_nmask);
 	if (!folio) {
-		*hpage = NULL;
+		*foliop = NULL;
 		count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
 		return SCAN_ALLOC_HUGE_PAGE_FAIL;
 	}
@@ -1063,13 +1063,13 @@ static int alloc_charge_hpage(struct page **hpage, struct mm_struct *mm,
 	count_vm_event(THP_COLLAPSE_ALLOC);
 	if (unlikely(mem_cgroup_charge(folio, mm, gfp))) {
 		folio_put(folio);
-		*hpage = NULL;
+		*foliop = NULL;
 		return SCAN_CGROUP_CHARGE_FAIL;
 	}
 
 	count_memcg_folio_events(folio, THP_COLLAPSE_ALLOC, 1);
 
-	*hpage = folio_page(folio, 0);
+	*foliop = folio;
 	return SCAN_SUCCEED;
 }
 
@@ -1098,7 +1098,8 @@ static int collapse_huge_page(struct mm_struct *mm, unsigned long address,
 	 */
 	mmap_read_unlock(mm);
 
-	result = alloc_charge_hpage(&hpage, mm, cc);
+	result = alloc_charge_folio(&folio, mm, cc);
+	hpage = &folio->page;
 	if (result != SCAN_SUCCEED)
 		goto out_nolock;
 
@@ -1204,7 +1205,6 @@ static int collapse_huge_page(struct mm_struct *mm, unsigned long address,
 	if (unlikely(result != SCAN_SUCCEED))
 		goto out_up_write;
 
-	folio = page_folio(hpage);
 	/*
 	 * The smp_wmb() inside __folio_mark_uptodate() ensures the
 	 * copy_huge_page writes become visible before the set_pmd_at()
@@ -1789,7 +1789,7 @@ static int collapse_file(struct mm_struct *mm, unsigned long addr,
 	struct page *hpage;
 	struct page *page;
 	struct page *tmp;
-	struct folio *folio;
+	struct folio *folio, *new_folio;
 	pgoff_t index = 0, end = start + HPAGE_PMD_NR;
 	LIST_HEAD(pagelist);
 	XA_STATE_ORDER(xas, &mapping->i_pages, start, HPAGE_PMD_ORDER);
@@ -1800,7 +1800,8 @@ static int collapse_file(struct mm_struct *mm, unsigned long addr,
 	VM_BUG_ON(!IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && !is_shmem);
 	VM_BUG_ON(start & (HPAGE_PMD_NR - 1));
 
-	result = alloc_charge_hpage(&hpage, mm, cc);
+	result = alloc_charge_folio(&new_folio, mm, cc);
+	hpage = &new_folio->page;
 	if (result != SCAN_SUCCEED)
 		goto out;