[RFC] pagecache_isize_extended

Matthew Wilcox
2024-01-17T16:16:16Z

I hadn't looked at pagecache_isize_extended() before, and I'm not
entirely sure it's doing the right thing for large folios. Usually
we decline to create folios which extend past EOF [1], and we try to split
folios on truncate. But folio splitting can fail, and I think we might
run into problems with a store to a folio which straddles i_size.

Do we have any xfstests which cover this? I'm not quite sure how to
write such a test.

[1] or at least EOF rounded up to PAGE_SIZE

diff --git a/mm/truncate.c b/mm/truncate.c
index 725b150e47ac..3025c579db52 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -781,8 +781,7 @@ void pagecache_isize_extended(struct inode *inode, loff_t from, loff_t to)
{
int bsize = i_blocksize(inode);
loff_t rounded_from;
- struct page *page;
- pgoff_t index;
+ struct folio *folio;

WARN_ON(to > inode->i_size);

@@ -793,19 +792,18 @@ void pagecache_isize_extended(struct inode *inode, loff_t from, loff_t to)
if (to <= rounded_from || !(rounded_from & (PAGE_SIZE - 1)))
return;

- index = from >> PAGE_SHIFT;
- page = find_lock_page(inode->i_mapping, index);
- /* Page not cached? Nothing to do */
- if (!page)
+ folio = filemap_lock_folio(inode->i_mapping, from / PAGE_SIZE);
+ /* Folio not cached? Nothing to do */
+ if (!folio)
return;
/*
- * See clear_page_dirty_for_io() for details why set_page_dirty()
+ * See folio_clear_dirty_for_io() for details why folio_mark_dirty()
* is needed.
*/
- if (page_mkclean(page))
- set_page_dirty(page);
- unlock_page(page);
- put_page(page);
+ if (folio_mkclean(folio))
+ folio_mark_dirty(folio);
+ folio_unlock(folio);
+ folio_put(folio);
}
EXPORT_SYMBOL(pagecache_isize_extended);