[PATCH v2 4/5] mm: swap: entirely map large folios found in swapcache

[Barry Song <21cnbao@gmail.com>]

From: Chuanhua Han <hanchuanhua@oppo.com>

When a large folio is found in the swapcache, the current implementation
requires calling do_swap_page() nr_pages times, resulting in nr_pages
page faults. This patch opts to map the entire large folio at once to
minimize page faults. Additionally, redundant checks and early exits
for ARM64 MTE restoring are removed.

Signed-off-by: Chuanhua Han <hanchuanhua@oppo.com>
Co-developed-by: Barry Song <v-songbaohua@oppo.com>
Signed-off-by: Barry Song <v-songbaohua@oppo.com>
---
 mm/memory.c | 64 +++++++++++++++++++++++++++++++++++++++++++----------
 1 file changed, 52 insertions(+), 12 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index c4a52e8d740a..9818dc1893c8 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3947,6 +3947,10 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 	pte_t pte;
 	vm_fault_t ret = 0;
 	void *shadow = NULL;
+	int nr_pages = 1;
+	unsigned long start_address = vmf->address;
+	pte_t *start_pte = vmf->pte;
+	bool any_swap_shared = false;
 
 	if (!pte_unmap_same(vmf))
 		goto out;
@@ -4137,6 +4141,35 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 	 */
 	vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd, vmf->address,
 			&vmf->ptl);
+
+	/* We hit large folios in swapcache */
+	if (start_pte && folio_test_large(folio) && folio_test_swapcache(folio)) {
+		int nr = folio_nr_pages(folio);
+		int idx = folio_page_idx(folio, page);
+		unsigned long folio_start = vmf->address - idx * PAGE_SIZE;
+		unsigned long folio_end = folio_start + nr * PAGE_SIZE;
+		pte_t *folio_ptep;
+		pte_t folio_pte;
+
+		if (unlikely(folio_start < max(vmf->address & PMD_MASK, vma->vm_start)))
+			goto check_pte;
+		if (unlikely(folio_end > pmd_addr_end(vmf->address, vma->vm_end)))
+			goto check_pte;
+
+		folio_ptep = vmf->pte - idx;
+		folio_pte = ptep_get(folio_ptep);
+		if (!is_swap_pte(folio_pte) || non_swap_entry(pte_to_swp_entry(folio_pte)) ||
+		    swap_pte_batch(folio_ptep, nr, folio_pte, &any_swap_shared) != nr)
+			goto check_pte;
+
+		start_address = folio_start;
+		start_pte = folio_ptep;
+		nr_pages = nr;
+		entry = folio->swap;
+		page = &folio->page;
+	}
+
+check_pte:
 	if (unlikely(!vmf->pte || !pte_same(ptep_get(vmf->pte), vmf->orig_pte)))
 		goto out_nomap;
 
@@ -4190,6 +4223,10 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 			 */
 			exclusive = false;
 		}
+
+		/* Reuse the whole large folio iff all entries are exclusive */
+		if (nr_pages > 1 && any_swap_shared)
+			exclusive = false;
 	}
 
 	/*
@@ -4204,12 +4241,14 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 	 * We're already holding a reference on the page but haven't mapped it
 	 * yet.
 	 */
-	swap_free(entry);
+	swap_free_nr(entry, nr_pages);
 	if (should_try_to_free_swap(folio, vma, vmf->flags))
 		folio_free_swap(folio);
 
-	inc_mm_counter(vma->vm_mm, MM_ANONPAGES);
-	dec_mm_counter(vma->vm_mm, MM_SWAPENTS);
+	folio_ref_add(folio, nr_pages - 1);
+	add_mm_counter(vma->vm_mm, MM_ANONPAGES, nr_pages);
+	add_mm_counter(vma->vm_mm, MM_SWAPENTS, -nr_pages);
+
 	pte = mk_pte(page, vma->vm_page_prot);
 
 	/*
@@ -4219,33 +4258,34 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 	 * exclusivity.
 	 */
 	if (!folio_test_ksm(folio) &&
-	    (exclusive || folio_ref_count(folio) == 1)) {
+	    (exclusive || (folio_ref_count(folio) == nr_pages &&
+			   folio_nr_pages(folio) == nr_pages))) {
 		if (vmf->flags & FAULT_FLAG_WRITE) {
 			pte = maybe_mkwrite(pte_mkdirty(pte), vma);
 			vmf->flags &= ~FAULT_FLAG_WRITE;
 		}
 		rmap_flags |= RMAP_EXCLUSIVE;
 	}
-	flush_icache_page(vma, page);
+	flush_icache_pages(vma, page, nr_pages);
 	if (pte_swp_soft_dirty(vmf->orig_pte))
 		pte = pte_mksoft_dirty(pte);
 	if (pte_swp_uffd_wp(vmf->orig_pte))
 		pte = pte_mkuffd_wp(pte);
-	vmf->orig_pte = pte;
 
 	/* ksm created a completely new copy */
 	if (unlikely(folio != swapcache && swapcache)) {
-		folio_add_new_anon_rmap(folio, vma, vmf->address);
+		folio_add_new_anon_rmap(folio, vma, start_address);
 		folio_add_lru_vma(folio, vma);
 	} else {
-		folio_add_anon_rmap_pte(folio, page, vma, vmf->address,
-					rmap_flags);
+		folio_add_anon_rmap_ptes(folio, page, nr_pages, vma, start_address,
+					 rmap_flags);
 	}
 
 	VM_BUG_ON(!folio_test_anon(folio) ||
 			(pte_write(pte) && !PageAnonExclusive(page)));
-	set_pte_at(vma->vm_mm, vmf->address, vmf->pte, pte);
-	arch_do_swap_page(vma->vm_mm, vma, vmf->address, pte, vmf->orig_pte);
+	set_ptes(vma->vm_mm, start_address, start_pte, pte, nr_pages);
+	vmf->orig_pte = ptep_get(vmf->pte);
+	arch_do_swap_page(vma->vm_mm, vma, start_address, pte, pte);
 
 	folio_unlock(folio);
 	if (folio != swapcache && swapcache) {
@@ -4269,7 +4309,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 	}
 
 	/* No need to invalidate - it was non-present before */
-	update_mmu_cache_range(vmf, vma, vmf->address, vmf->pte, 1);
+	update_mmu_cache_range(vmf, vma, start_address, start_pte, nr_pages);
 unlock:
 	if (vmf->pte)
 		pte_unmap_unlock(vmf->pte, vmf->ptl);
-- 
2.34.1