mm/rmap: remove duplicated exit code in pagewalk loop

Patch series "Reclaim lazyfree THP without splitting", v8.

This series adds support for reclaiming PMD-mapped THP marked as lazyfree
without needing to first split the large folio via
split_huge_pmd_address().

When the user no longer requires the pages, they would use
madvise(MADV_FREE) to mark the pages as lazy free.  Subsequently, they
typically would not re-write to that memory again.

During memory reclaim, if we detect that the large folio and its PMD are
both still marked as clean and there are no unexpected references(such as
GUP), so we can just discard the memory lazily, improving the efficiency
of memory reclamation in this case.

Performance Testing
===================

On an Intel i5 CPU, reclaiming 1GiB of lazyfree THPs using
mem_cgroup_force_empty() results in the following runtimes in seconds
(shorter is better):

--------------------------------------------
|     Old       |      New       |  Change  |
--------------------------------------------
|   0.683426    |    0.049197    |  -92.80% |
--------------------------------------------


This patch (of 8):

Introduce the labels walk_done and walk_abort as exit points to eliminate
duplicated exit code in the pagewalk loop.

Link: https://lkml.kernel.org/r/20240614015138.31461-1-ioworker0@gmail.com
Link: https://lkml.kernel.org/r/20240614015138.31461-2-ioworker0@gmail.comSigned-off-by: Lance Yang <ioworker0@gmail.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Barry Song <baohua@kernel.org>
Cc: Bang Li <libang.li@antgroup.com>
Cc: Fangrui Song <maskray@google.com>
Cc: Jeff Xie <xiehuan09@gmail.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: SeongJae Park <sj@kernel.org>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Yin Fengwei <fengwei.yin@intel.com>
Cc: Zach O'Keefe <zokeefe@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/rmap.c

@@ -1681,9 +1681,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
 			/* Restore the mlock which got missed */
 			if (!folio_test_large(folio))
 				mlock_vma_folio(folio, vma);
-			page_vma_mapped_walk_done(&pvmw);
-			ret = false;
-			break;
+			goto walk_abort;
 		}
 
 		pfn = pte_pfn(ptep_get(pvmw.pte));
@@ -1721,11 +1719,8 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
 			 */
 			if (!anon) {
 				VM_BUG_ON(!(flags & TTU_RMAP_LOCKED));
-				if (!hugetlb_vma_trylock_write(vma)) {
-					page_vma_mapped_walk_done(&pvmw);
-					ret = false;
-					break;
-				}
+				if (!hugetlb_vma_trylock_write(vma))
+					goto walk_abort;
 				if (huge_pmd_unshare(mm, vma, address, pvmw.pte)) {
 					hugetlb_vma_unlock_write(vma);
 					flush_tlb_range(vma,
@@ -1740,8 +1735,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
 					 * actual page and drop map count
 					 * to zero.
 					 */
-					page_vma_mapped_walk_done(&pvmw);
-					break;
+					goto walk_done;
 				}
 				hugetlb_vma_unlock_write(vma);
 			}
@@ -1813,9 +1807,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
 			if (unlikely(folio_test_swapbacked(folio) !=
 					folio_test_swapcache(folio))) {
 				WARN_ON_ONCE(1);
-				ret = false;
-				page_vma_mapped_walk_done(&pvmw);
-				break;
+				goto walk_abort;
 			}
 
 			/* MADV_FREE page check */
@@ -1854,23 +1846,17 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
 				 */
 				set_pte_at(mm, address, pvmw.pte, pteval);
 				folio_set_swapbacked(folio);
-				ret = false;
-				page_vma_mapped_walk_done(&pvmw);
-				break;
+				goto walk_abort;
 			}
 
 			if (swap_duplicate(entry) < 0) {
 				set_pte_at(mm, address, pvmw.pte, pteval);
-				ret = false;
-				page_vma_mapped_walk_done(&pvmw);
-				break;
+				goto walk_abort;
 			}
 			if (arch_unmap_one(mm, vma, address, pteval) < 0) {
 				swap_free(entry);
 				set_pte_at(mm, address, pvmw.pte, pteval);
-				ret = false;
-				page_vma_mapped_walk_done(&pvmw);
-				break;
+				goto walk_abort;
 			}
 
 			/* See folio_try_share_anon_rmap(): clear PTE first. */
@@ -1878,9 +1864,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
 			    folio_try_share_anon_rmap_pte(folio, subpage)) {
 				swap_free(entry);
 				set_pte_at(mm, address, pvmw.pte, pteval);
-				ret = false;
-				page_vma_mapped_walk_done(&pvmw);
-				break;
+				goto walk_abort;
 			}
 			if (list_empty(&mm->mmlist)) {
 				spin_lock(&mmlist_lock);
@@ -1920,6 +1904,12 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
 		if (vma->vm_flags & VM_LOCKED)
 			mlock_drain_local();
 		folio_put(folio);
+		continue;
+walk_abort:
+		ret = false;
+walk_done:
+		page_vma_mapped_walk_done(&pvmw);
+		break;
 	}
 
 	mmu_notifier_invalidate_range_end(&range);