filemap: find_get_entries() now updates start offset

Initially, find_get_entries() was being passed in the start offset as a
value.  That left the calculation of the offset to the callers.  This led
to complexity in the callers trying to keep track of the index.

Now find_get_entries() takes in a pointer to the start offset and updates
the value to be directly after the last entry found.  If no entry is
found, the offset is not changed.  This gets rid of multiple hacky
calculations that kept track of the start offset.

Link: https://lkml.kernel.org/r/20221017161800.2003-3-vishal.moola@gmail.comSigned-off-by: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/filemap.c

@@ -2048,10 +2048,10 @@ static inline struct folio *find_get_entry(struct xa_state *xas, pgoff_t max,
  *
  * Return: The number of entries which were found.
  */
-unsigned find_get_entries(struct address_space *mapping, pgoff_t start,
+unsigned find_get_entries(struct address_space *mapping, pgoff_t *start,
 		pgoff_t end, struct folio_batch *fbatch, pgoff_t *indices)
 {
-	XA_STATE(xas, &mapping->i_pages, start);
+	XA_STATE(xas, &mapping->i_pages, *start);
 	struct folio *folio;
 
 	rcu_read_lock();
@@ -2062,6 +2062,15 @@ unsigned find_get_entries(struct address_space *mapping, pgoff_t start,
 	}
 	rcu_read_unlock();
 
+	if (folio_batch_count(fbatch)) {
+		unsigned long nr = 1;
+		int idx = folio_batch_count(fbatch) - 1;
+
+		folio = fbatch->folios[idx];
+		if (!xa_is_value(folio) && !folio_test_hugetlb(folio))
+			nr = folio_nr_pages(folio);
+		*start = indices[idx] + nr;
+	}
 	return folio_batch_count(fbatch);
 }
 

mm/internal.h

@@ -108,7 +108,7 @@ static inline void force_page_cache_readahead(struct address_space *mapping,
 
 unsigned find_lock_entries(struct address_space *mapping, pgoff_t *start,
 		pgoff_t end, struct folio_batch *fbatch, pgoff_t *indices);
-unsigned find_get_entries(struct address_space *mapping, pgoff_t start,
+unsigned find_get_entries(struct address_space *mapping, pgoff_t *start,
 		pgoff_t end, struct folio_batch *fbatch, pgoff_t *indices);
 void filemap_free_folio(struct address_space *mapping, struct folio *folio);
 int truncate_inode_folio(struct address_space *mapping, struct folio *folio);

mm/shmem.c

@@ -973,7 +973,7 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend,
 	while (index < end) {
 		cond_resched();
 
-		if (!find_get_entries(mapping, index, end - 1, &fbatch,
+		if (!find_get_entries(mapping, &index, end - 1, &fbatch,
 				indices)) {
 			/* If all gone or hole-punch or unfalloc, we're done */
 			if (index == start || end != -1)
@@ -985,13 +985,12 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend,
 		for (i = 0; i < folio_batch_count(&fbatch); i++) {
 			folio = fbatch.folios[i];
 
-			index = indices[i];
 			if (xa_is_value(folio)) {
 				if (unfalloc)
 					continue;
-				if (shmem_free_swap(mapping, index, folio)) {
+				if (shmem_free_swap(mapping, indices[i], folio)) {
 					/* Swap was replaced by page: retry */
-					index--;
+					index = indices[i];
 					break;
 				}
 				nr_swaps_freed++;
@@ -1004,19 +1003,17 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend,
 				if (folio_mapping(folio) != mapping) {
 					/* Page was replaced by swap: retry */
 					folio_unlock(folio);
-					index--;
+					index = indices[i];
 					break;
 				}
 				VM_BUG_ON_FOLIO(folio_test_writeback(folio),
 						folio);
 				truncate_inode_folio(mapping, folio);
 			}
-			index = folio->index + folio_nr_pages(folio) - 1;
 			folio_unlock(folio);
 		}
 		folio_batch_remove_exceptionals(&fbatch);
 		folio_batch_release(&fbatch);
-		index++;
 	}
 
 	spin_lock_irq(&info->lock);

mm/truncate.c

@@ -400,7 +400,7 @@ void truncate_inode_pages_range(struct address_space *mapping,
 	index = start;
 	while (index < end) {
 		cond_resched();
-		if (!find_get_entries(mapping, index, end - 1, &fbatch,
+		if (!find_get_entries(mapping, &index, end - 1, &fbatch,
 				indices)) {
 			/* If all gone from start onwards, we're done */
 			if (index == start)
@@ -414,21 +414,18 @@ void truncate_inode_pages_range(struct address_space *mapping,
 			struct folio *folio = fbatch.folios[i];
 
 			/* We rely upon deletion not changing page->index */
-			index = indices[i];
 
 			if (xa_is_value(folio))
 				continue;
 
 			folio_lock(folio);
-			VM_BUG_ON_FOLIO(!folio_contains(folio, index), folio);
+			VM_BUG_ON_FOLIO(!folio_contains(folio, indices[i]), folio);
 			folio_wait_writeback(folio);
 			truncate_inode_folio(mapping, folio);
 			folio_unlock(folio);
-			index = folio_index(folio) + folio_nr_pages(folio) - 1;
 		}
 		truncate_folio_batch_exceptionals(mapping, &fbatch, indices);
 		folio_batch_release(&fbatch);
-		index++;
 	}
 }
 EXPORT_SYMBOL(truncate_inode_pages_range);
@@ -636,16 +633,15 @@ int invalidate_inode_pages2_range(struct address_space *mapping,
 
 	folio_batch_init(&fbatch);
 	index = start;
-	while (find_get_entries(mapping, index, end, &fbatch, indices)) {
+	while (find_get_entries(mapping, &index, end, &fbatch, indices)) {
 		for (i = 0; i < folio_batch_count(&fbatch); i++) {
 			struct folio *folio = fbatch.folios[i];
 
 			/* We rely upon deletion not changing folio->index */
-			index = indices[i];
 
 			if (xa_is_value(folio)) {
 				if (!invalidate_exceptional_entry2(mapping,
-						index, folio))
+						indices[i], folio))
 					ret = -EBUSY;
 				continue;
 			}
@@ -655,13 +651,13 @@ int invalidate_inode_pages2_range(struct address_space *mapping,
 				 * If folio is mapped, before taking its lock,
 				 * zap the rest of the file in one hit.
 				 */
-				unmap_mapping_pages(mapping, index,
-						(1 + end - index), false);
+				unmap_mapping_pages(mapping, indices[i],
+						(1 + end - indices[i]), false);
 				did_range_unmap = 1;
 			}
 
 			folio_lock(folio);
-			VM_BUG_ON_FOLIO(!folio_contains(folio, index), folio);
+			VM_BUG_ON_FOLIO(!folio_contains(folio, indices[i]), folio);
 			if (folio->mapping != mapping) {
 				folio_unlock(folio);
 				continue;
@@ -684,7 +680,6 @@ int invalidate_inode_pages2_range(struct address_space *mapping,
 		folio_batch_remove_exceptionals(&fbatch);
 		folio_batch_release(&fbatch);
 		cond_resched();
-		index++;
 	}
 	/*
 	 * For DAX we invalidate page tables after invalidating page cache.  We