[PATCH RFC 07/12] mm/gup: Refactor record_subpages() to find 1st small page

[Peter Xu <peterx@redhat.com>]

All the fast-gup functions take a tail page to operate, always need to do
page mask calculations before feeding that into record_subpages().

Merge that logic into record_subpages(), so that we always take a head
page, and leave the rest calculation to record_subpages().

Signed-off-by: Peter Xu <peterx@redhat.com>
---
 mm/gup.c | 23 +++++++++++++----------
 1 file changed, 13 insertions(+), 10 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index 424d45e1afb3..69dae51f3eb1 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -2763,11 +2763,14 @@ static int __gup_device_huge_pud(pud_t pud, pud_t *pudp, unsigned long addr,
 }
 #endif
 
-static int record_subpages(struct page *page, unsigned long addr,
-			   unsigned long end, struct page **pages)
+static int record_subpages(struct page *head, unsigned long sz,
+			   unsigned long addr, unsigned long end,
+			   struct page **pages)
 {
+	struct page *page;
 	int nr;
 
+	page = nth_page(head, (addr & (sz - 1)) >> PAGE_SHIFT);
 	for (nr = 0; addr != end; nr++, addr += PAGE_SIZE)
 		pages[nr] = nth_page(page, nr);
 
@@ -2804,8 +2807,8 @@ static int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr,
 	/* hugepages are never "special" */
 	VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
 
-	page = nth_page(pte_page(pte), (addr & (sz - 1)) >> PAGE_SHIFT);
-	refs = record_subpages(page, addr, end, pages + *nr);
+	page = pte_page(pte);
+	refs = record_subpages(page, sz, addr, end, pages + *nr);
 
 	folio = try_grab_folio(page, refs, flags);
 	if (!folio)
@@ -2870,8 +2873,8 @@ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
 					     pages, nr);
 	}
 
-	page = nth_page(pmd_page(orig), (addr & ~PMD_MASK) >> PAGE_SHIFT);
-	refs = record_subpages(page, addr, end, pages + *nr);
+	page = pmd_page(orig);
+	refs = record_subpages(page, PMD_SIZE, addr, end, pages + *nr);
 
 	folio = try_grab_folio(page, refs, flags);
 	if (!folio)
@@ -2914,8 +2917,8 @@ static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
 					     pages, nr);
 	}
 
-	page = nth_page(pud_page(orig), (addr & ~PUD_MASK) >> PAGE_SHIFT);
-	refs = record_subpages(page, addr, end, pages + *nr);
+	page = pud_page(orig);
+	refs = record_subpages(page, PUD_SIZE, addr, end, pages + *nr);
 
 	folio = try_grab_folio(page, refs, flags);
 	if (!folio)
@@ -2954,8 +2957,8 @@ static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr,
 
 	BUILD_BUG_ON(pgd_devmap(orig));
 
-	page = nth_page(pgd_page(orig), (addr & ~PGDIR_MASK) >> PAGE_SHIFT);
-	refs = record_subpages(page, addr, end, pages + *nr);
+	page = pgd_page(orig);
+	refs = record_subpages(page, PGDIR_SIZE, addr, end, pages + *nr);
 
 	folio = try_grab_folio(page, refs, flags);
 	if (!folio)
-- 
2.41.0