[PATCH] mm: Convert pagecache_isize_extended to use a folio

[PATCH] mm: Convert pagecache_isize_extended to use a folio

[Matthew Wilcox (Oracle)]

Remove four hidden calls to compound_head().  Also exit early if the
filesystem block size is >= PAGE_SIZE instead of just equal to PAGE_SIZE.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Pankaj Raghav <p.raghav@samsung.com>
---
 mm/truncate.c | 36 +++++++++++++++++-------------------
 1 file changed, 17 insertions(+), 19 deletions(-)

diff --git a/mm/truncate.c b/mm/truncate.c
index 725b150e47ac..e99085bf3d34 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -764,15 +764,15 @@ EXPORT_SYMBOL(truncate_setsize);
  * @from:	original inode size
  * @to:		new inode size
  *
- * Handle extension of inode size either caused by extending truncate or by
- * write starting after current i_size. We mark the page straddling current
- * i_size RO so that page_mkwrite() is called on the nearest write access to
- * the page.  This way filesystem can be sure that page_mkwrite() is called on
- * the page before user writes to the page via mmap after the i_size has been
- * changed.
+ * Handle extension of inode size either caused by extending truncate or
+ * by write starting after current i_size.  We mark the page straddling
+ * current i_size RO so that page_mkwrite() is called on the first
+ * write access to the page.  The filesystem will update its per-block
+ * information before user writes to the page via mmap after the i_size
+ * has been changed.
  *
  * The function must be called after i_size is updated so that page fault
- * coming after we unlock the page will already see the new i_size.
+ * coming after we unlock the folio will already see the new i_size.
  * The function must be called while we still hold i_rwsem - this not only
  * makes sure i_size is stable but also that userspace cannot observe new
  * i_size value before we are prepared to store mmap writes at new inode size.
@@ -781,31 +781,29 @@ 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);
 
-	if (from >= to || bsize == PAGE_SIZE)
+	if (from >= to || bsize >= PAGE_SIZE)
 		return;
 	/* Page straddling @from will not have any hole block created? */
 	rounded_from = round_up(from, bsize);
 	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 (IS_ERR(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);
 
-- 
2.43.0

Re: [PATCH] mm: Convert pagecache_isize_extended to use a folio

[David Hildenbrand]

On 05.04.24 20:00, Matthew Wilcox (Oracle) wrote:
> Remove four hidden calls to compound_head().  Also exit early if the
> filesystem block size is >= PAGE_SIZE instead of just equal to PAGE_SIZE.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> Reviewed-by: Pankaj Raghav <p.raghav@samsung.com>
> ---
>   mm/truncate.c | 36 +++++++++++++++++-------------------
>   1 file changed, 17 insertions(+), 19 deletions(-)
> 
> diff --git a/mm/truncate.c b/mm/truncate.c
> index 725b150e47ac..e99085bf3d34 100644
> --- a/mm/truncate.c
> +++ b/mm/truncate.c
> @@ -764,15 +764,15 @@ EXPORT_SYMBOL(truncate_setsize);
>    * @from:	original inode size
>    * @to:		new inode size
>    *
> - * Handle extension of inode size either caused by extending truncate or by
> - * write starting after current i_size. We mark the page straddling current
> - * i_size RO so that page_mkwrite() is called on the nearest write access to
> - * the page.  This way filesystem can be sure that page_mkwrite() is called on
> - * the page before user writes to the page via mmap after the i_size has been
> - * changed.
> + * Handle extension of inode size either caused by extending truncate or
> + * by write starting after current i_size.  We mark the page straddling
> + * current i_size RO so that page_mkwrite() is called on the first
> + * write access to the page.  The filesystem will update its per-block
> + * information before user writes to the page via mmap after the i_size
> + * has been changed.

Did you intend not to s/page/folio/ ?

>    *
>    * The function must be called after i_size is updated so that page fault
> - * coming after we unlock the page will already see the new i_size.
> + * coming after we unlock the folio will already see the new i_size.
>    * The function must be called while we still hold i_rwsem - this not only
>    * makes sure i_size is stable but also that userspace cannot observe new
>    * i_size value before we are prepared to store mmap writes at new inode size.
> @@ -781,31 +781,29 @@ void pagecache_isize_extended(struct inode *inode, loff_t from, loff_t to)


Reviewed-by: David Hildenbrand <david@redhat.com>

-- 
Cheers,

David / dhildenb

Re: [PATCH] mm: Convert pagecache_isize_extended to use a folio

[Matthew Wilcox]

On Tue, Apr 09, 2024 at 03:39:35PM +0200, David Hildenbrand wrote:
> On 05.04.24 20:00, Matthew Wilcox (Oracle) wrote:
> > + * Handle extension of inode size either caused by extending truncate or
> > + * by write starting after current i_size.  We mark the page straddling
> > + * current i_size RO so that page_mkwrite() is called on the first
> > + * write access to the page.  The filesystem will update its per-block
> > + * information before user writes to the page via mmap after the i_size
> > + * has been changed.
> 
> Did you intend not to s/page/folio/ ?

I did!  I think here we're talking about page faults, and we can control
the RO property on a per-PTE (ie per-page) basis.  Do you think it'd be
clearer if we talked about folios here?  We're in a bit of an interesting
spot because filesystems generally don't have folios which overhang the
end of the file by more than a page.  It can happen if truncate fails
to split a folio.

> Reviewed-by: David Hildenbrand <david@redhat.com>

Thanks!