filemap: find_lock_entries() now updates start offset

Patch series "Rework find_get_entries() and find_lock_entries()", v3.

Originally the callers of find_get_entries() and find_lock_entries() were
keeping track of the start index themselves as they traverse the search
range.

This resulted in hacky code such as in shmem_undo_range():

			index = folio->index + folio_nr_pages(folio) - 1;

where the - 1 is only present to stay in the right spot after incrementing
index later.  This sort of calculation was also being done on every folio
despite not even using index later within that function.

These patches change find_get_entries() and find_lock_entries() to
calculate the new index instead of leaving it to the callers so we can
avoid all these complications.


This patch (of 2):

Initially, find_lock_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_lock_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/20221017161800.2003-1-vishal.moola@gmail.com
Link: https://lkml.kernel.org/r/20221017161800.2003-2-vishal.moola@gmail.com
Signed-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

@@ -2085,16 +2085,16 @@ unsigned find_get_entries(struct address_space *mapping, pgoff_t start,
  *
  * Return: The number of entries which were found.
  */
-unsigned find_lock_entries(struct address_space *mapping, pgoff_t start,
+unsigned find_lock_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();
 	while ((folio = find_get_entry(&xas, end, XA_PRESENT))) {
 		if (!xa_is_value(folio)) {
-			if (folio->index < start)
+			if (folio->index < *start)
 				goto put;
 			if (folio->index + folio_nr_pages(folio) - 1 > end)
 				goto put;
@@ -2117,6 +2117,15 @@ put:
 	}
 	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

@@ -106,7 +106,7 @@ static inline void force_page_cache_readahead(struct address_space *mapping,
 	force_page_cache_ra(&ractl, nr_to_read);
 }
 
-unsigned find_lock_entries(struct address_space *mapping, pgoff_t start,
+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,
 		pgoff_t end, struct folio_batch *fbatch, pgoff_t *indices);

mm/shmem.c

@@ -922,21 +922,18 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend,
 
 	folio_batch_init(&fbatch);
 	index = start;
-	while (index < end && find_lock_entries(mapping, index, end - 1,
+	while (index < end && find_lock_entries(mapping, &index, end - 1,
 			&fbatch, indices)) {
 		for (i = 0; i < folio_batch_count(&fbatch); i++) {
 			folio = fbatch.folios[i];
 
-			index = indices[i];
-
 			if (xa_is_value(folio)) {
 				if (unfalloc)
 					continue;
 				nr_swaps_freed += !shmem_free_swap(mapping,
-								index, folio);
+							indices[i], folio);
 				continue;
 			}
-			index += folio_nr_pages(folio) - 1;
 
 			if (!unfalloc || !folio_test_uptodate(folio))
 				truncate_inode_folio(mapping, folio);
@@ -945,7 +942,6 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend,
 		folio_batch_remove_exceptionals(&fbatch);
 		folio_batch_release(&fbatch);
 		cond_resched();
-		index++;
 	}
 
 	same_folio = (lstart >> PAGE_SHIFT) == (lend >> PAGE_SHIFT);

mm/truncate.c

@@ -361,9 +361,8 @@ void truncate_inode_pages_range(struct address_space *mapping,
 
 	folio_batch_init(&fbatch);
 	index = start;
-	while (index < end && find_lock_entries(mapping, index, end - 1,
+	while (index < end && find_lock_entries(mapping, &index, end - 1,
 			&fbatch, indices)) {
-		index = indices[folio_batch_count(&fbatch) - 1] + 1;
 		truncate_folio_batch_exceptionals(mapping, &fbatch, indices);
 		for (i = 0; i < folio_batch_count(&fbatch); i++)
 			truncate_cleanup_folio(fbatch.folios[i]);
@@ -510,20 +509,17 @@ unsigned long invalidate_mapping_pagevec(struct address_space *mapping,
 	int i;
 
 	folio_batch_init(&fbatch);
-	while (find_lock_entries(mapping, index, end, &fbatch, indices)) {
+	while (find_lock_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)) {
 				count += invalidate_exceptional_entry(mapping,
-								      index,
-								      folio);
+							     indices[i], folio);
 				continue;
 			}
-			index += folio_nr_pages(folio) - 1;
 
 			ret = mapping_evict_folio(mapping, folio);
 			folio_unlock(folio);
@@ -542,7 +538,6 @@ unsigned long invalidate_mapping_pagevec(struct address_space *mapping,
 		folio_batch_remove_exceptionals(&fbatch);
 		folio_batch_release(&fbatch);
 		cond_resched();
-		index++;
 	}
 	return count;
 }