swapfile: convert unuse_pte_range() to use a folio

Delay fetching the precise page from the folio until we're in unuse_pte().
Saves many calls to compound_head().

Link: https://lkml.kernel.org/r/20220902194653.1739778-37-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/swapfile.c b/mm/swapfile.c
index e3e1bd3..3820b5a 100644 (file)
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1758,8 +1758,9 @@ static inline int pte_same_as_swp(pte_t pte, pte_t swp_pte)
  * force COW, vm_page_prot omits write permission from any private vma.
  */
 static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
-               unsigned long addr, swp_entry_t entry, struct page *page)
+               unsigned long addr, swp_entry_t entry, struct folio *folio)
 {
+       struct page *page = folio_file_page(folio, swp_offset(entry));
        struct page *swapcache;
        spinlock_t *ptl;
        pte_t *pte, new_pte;
@@ -1831,17 +1832,18 @@ static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
                        unsigned long addr, unsigned long end,
                        unsigned int type)
 {
-       struct page *page;
        swp_entry_t entry;
        pte_t *pte;
        struct swap_info_struct *si;
-       unsigned long offset;
        int ret = 0;
        volatile unsigned char *swap_map;
 
        si = swap_info[type];
        pte = pte_offset_map(pmd, addr);
        do {
+               struct folio *folio;
+               unsigned long offset;
+
                if (!is_swap_pte(*pte))
                        continue;
 
@@ -1852,8 +1854,9 @@ static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
                offset = swp_offset(entry);
                pte_unmap(pte);
                swap_map = &si->swap_map[offset];
-               page = lookup_swap_cache(entry, vma, addr);
-               if (!page) {
+               folio = swap_cache_get_folio(entry, vma, addr);
+               if (!folio) {
+                       struct page *page;
                        struct vm_fault vmf = {
                                .vma = vma,
                                .address = addr,
@@ -1863,25 +1866,27 @@ static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
 
                        page = swapin_readahead(entry, GFP_HIGHUSER_MOVABLE,
                                                &vmf);
+                       if (page)
+                               folio = page_folio(page);
                }
-               if (!page) {
+               if (!folio) {
                        if (*swap_map == 0 || *swap_map == SWAP_MAP_BAD)
                                goto try_next;
                        return -ENOMEM;
                }
 
-               lock_page(page);
-               wait_on_page_writeback(page);
-               ret = unuse_pte(vma, pmd, addr, entry, page);
+               folio_lock(folio);
+               folio_wait_writeback(folio);
+               ret = unuse_pte(vma, pmd, addr, entry, folio);
                if (ret < 0) {
-                       unlock_page(page);
-                       put_page(page);
+                       folio_unlock(folio);
+                       folio_put(folio);
                        goto out;
                }
 
-               try_to_free_swap(page);
-               unlock_page(page);
-               put_page(page);
+               folio_free_swap(folio);
+               folio_unlock(folio);
+               folio_put(folio);
 try_next:
                pte = pte_offset_map(pmd, addr);
        } while (pte++, addr += PAGE_SIZE, addr != end);