mm/khugepaged: minor reorderings in collapse_shmem()

commit 042a3082 upstream.

Several cleanups in collapse_shmem(): most of which probably do not
really matter, beyond doing things in a more familiar and reassuring
order.  Simplify the failure gotos in the main loop, and on success
update stats while interrupts still disabled from the last iteration.

Link: http://lkml.kernel.org/r/alpine.LSU.2.11.1811261526400.2275@eggly.anvils
Fixes: f3f0e1d2 ("khugepaged: add support of collapse for tmpfs/shmem pages")
Signed-off-by: Hugh Dickins <hughd@google.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: <stable@vger.kernel.org>	[4.8+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

mm/khugepaged.c

@@ -1330,13 +1330,12 @@ static void collapse_shmem(struct mm_struct *mm,
 		goto out;
 	}
 
+	__SetPageLocked(new_page);
+	__SetPageSwapBacked(new_page);
 	new_page->index = start;
 	new_page->mapping = mapping;
-	__SetPageSwapBacked(new_page);
-	__SetPageLocked(new_page);
 	BUG_ON(!page_ref_freeze(new_page, 1));
 
-
 	/*
 	 * At this point the new_page is 'frozen' (page_count() is zero), locked
 	 * and not up-to-date. It's safe to insert it into radix tree, because
@@ -1365,13 +1364,13 @@ static void collapse_shmem(struct mm_struct *mm,
 		 */
 		if (n && !shmem_charge(mapping->host, n)) {
 			result = SCAN_FAIL;
-			break;
+			goto tree_locked;
 		}
-		nr_none += n;
 		for (; index < min(iter.index, end); index++) {
 			radix_tree_insert(&mapping->i_pages, index,
 					new_page + (index % HPAGE_PMD_NR));
 		}
+		nr_none += n;
 
 		/* We are done. */
 		if (index >= end)
@@ -1387,12 +1386,12 @@ static void collapse_shmem(struct mm_struct *mm,
 				result = SCAN_FAIL;
 				goto tree_unlocked;
 			}
-			xa_lock_irq(&mapping->i_pages);
 		} else if (trylock_page(page)) {
 			get_page(page);
+			xa_unlock_irq(&mapping->i_pages);
 		} else {
 			result = SCAN_PAGE_LOCK;
-			break;
+			goto tree_locked;
 		}
 
 		/*
@@ -1407,11 +1406,10 @@ static void collapse_shmem(struct mm_struct *mm,
 			result = SCAN_TRUNCATED;
 			goto out_unlock;
 		}
-		xa_unlock_irq(&mapping->i_pages);
 
 		if (isolate_lru_page(page)) {
 			result = SCAN_DEL_PAGE_LRU;
-			goto out_isolate_failed;
+			goto out_unlock;
 		}
 
 		if (page_mapped(page))
@@ -1432,7 +1430,9 @@ static void collapse_shmem(struct mm_struct *mm,
 		 */
 		if (!page_ref_freeze(page, 3)) {
 			result = SCAN_PAGE_COUNT;
-			goto out_lru;
+			xa_unlock_irq(&mapping->i_pages);
+			putback_lru_page(page);
+			goto out_unlock;
 		}
 
 		/*
@@ -1448,17 +1448,10 @@ static void collapse_shmem(struct mm_struct *mm,
 		slot = radix_tree_iter_resume(slot, &iter);
 		index++;
 		continue;
-out_lru:
-		xa_unlock_irq(&mapping->i_pages);
-		putback_lru_page(page);
-out_isolate_failed:
-		unlock_page(page);
-		put_page(page);
-		goto tree_unlocked;
 out_unlock:
 		unlock_page(page);
 		put_page(page);
-		break;
+		goto tree_unlocked;
 	}
 
 	/*
@@ -1466,7 +1459,7 @@ static void collapse_shmem(struct mm_struct *mm,
 	 * This code only triggers if there's nothing in radix tree
 	 * beyond 'end'.
 	 */
-	if (result == SCAN_SUCCEED && index < end) {
+	if (index < end) {
 		int n = end - index;
 
 		/* Stop if extent has been truncated, and is now empty */
@@ -1478,7 +1471,6 @@ static void collapse_shmem(struct mm_struct *mm,
 			result = SCAN_FAIL;
 			goto tree_locked;
 		}
-
 		for (; index < end; index++) {
 			radix_tree_insert(&mapping->i_pages, index,
 					new_page + (index % HPAGE_PMD_NR));
@@ -1486,14 +1478,19 @@ static void collapse_shmem(struct mm_struct *mm,
 		nr_none += n;
 	}
 
+	__inc_node_page_state(new_page, NR_SHMEM_THPS);
+	if (nr_none) {
+		struct zone *zone = page_zone(new_page);
+
+		__mod_node_page_state(zone->zone_pgdat, NR_FILE_PAGES, nr_none);
+		__mod_node_page_state(zone->zone_pgdat, NR_SHMEM, nr_none);
+	}
+
 tree_locked:
 	xa_unlock_irq(&mapping->i_pages);
 tree_unlocked:
 
 	if (result == SCAN_SUCCEED) {
-		unsigned long flags;
-		struct zone *zone = page_zone(new_page);
-
 		/*
 		 * Replacing old pages with new one has succeed, now we need to
 		 * copy the content and free old pages.
@@ -1507,11 +1504,11 @@ static void collapse_shmem(struct mm_struct *mm,
 			copy_highpage(new_page + (page->index % HPAGE_PMD_NR),
 					page);
 			list_del(&page->lru);
-			unlock_page(page);
-			page_ref_unfreeze(page, 1);
 			page->mapping = NULL;
+			page_ref_unfreeze(page, 1);
 			ClearPageActive(page);
 			ClearPageUnevictable(page);
+			unlock_page(page);
 			put_page(page);
 			index++;
 		}
@@ -1520,28 +1517,17 @@ static void collapse_shmem(struct mm_struct *mm,
 			index++;
 		}
 
-		local_irq_save(flags);
-		__inc_node_page_state(new_page, NR_SHMEM_THPS);
-		if (nr_none) {
-			__mod_node_page_state(zone->zone_pgdat, NR_FILE_PAGES, nr_none);
-			__mod_node_page_state(zone->zone_pgdat, NR_SHMEM, nr_none);
-		}
-		local_irq_restore(flags);
-
-		/*
-		 * Remove pte page tables, so we can re-faulti
-		 * the page as huge.
-		 */
-		retract_page_tables(mapping, start);
-
 		/* Everything is ready, let's unfreeze the new_page */
-		set_page_dirty(new_page);
 		SetPageUptodate(new_page);
 		page_ref_unfreeze(new_page, HPAGE_PMD_NR);
+		set_page_dirty(new_page);
 		mem_cgroup_commit_charge(new_page, memcg, false, true);
 		lru_cache_add_anon(new_page);
-		unlock_page(new_page);
 
+		/*
+		 * Remove pte page tables, so we can re-fault the page as huge.
+		 */
+		retract_page_tables(mapping, start);
 		*hpage = NULL;
 
 		khugepaged_pages_collapsed++;
@@ -1573,8 +1559,8 @@ static void collapse_shmem(struct mm_struct *mm,
 			radix_tree_replace_slot(&mapping->i_pages, slot, page);
 			slot = radix_tree_iter_resume(slot, &iter);
 			xa_unlock_irq(&mapping->i_pages);
-			putback_lru_page(page);
 			unlock_page(page);
+			putback_lru_page(page);
 			xa_lock_irq(&mapping->i_pages);
 		}
 		VM_BUG_ON(nr_none);
@@ -1583,9 +1569,10 @@ static void collapse_shmem(struct mm_struct *mm,
 		/* Unfreeze new_page, caller would take care about freeing it */
 		page_ref_unfreeze(new_page, 1);
 		mem_cgroup_cancel_charge(new_page, memcg, true);
-		unlock_page(new_page);
 		new_page->mapping = NULL;
 	}
+
+	unlock_page(new_page);
 out:
 	VM_BUG_ON(!list_empty(&pagelist));
 	/* TODO: tracepoints */