[v2,11/25] fs: Make page_mkwrite_check_truncate thp-aware
diff mbox series

Message ID 20200212041845.25879-12-willy@infradead.org
State New
Headers show
Series
  • Large pages in the page cache
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Commit Message

Matthew Wilcox Feb. 12, 2020, 4:18 a.m. UTC
From: "Matthew Wilcox (Oracle)" <willy@infradead.org>

If the page is compound, check the appropriate indices and return the
appropriate sizes.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 include/linux/pagemap.h | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

Comments

Kirill A. Shutemov Feb. 13, 2020, 3:44 p.m. UTC | #1
On Tue, Feb 11, 2020 at 08:18:31PM -0800, Matthew Wilcox wrote:
> From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
> 
> If the page is compound, check the appropriate indices and return the
> appropriate sizes.

Is it guarnteed that the page is never called on tail page?
Matthew Wilcox Feb. 13, 2020, 4:26 p.m. UTC | #2
On Thu, Feb 13, 2020 at 06:44:19PM +0300, Kirill A. Shutemov wrote:
> On Tue, Feb 11, 2020 at 08:18:31PM -0800, Matthew Wilcox wrote:
> > From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
> > 
> > If the page is compound, check the appropriate indices and return the
> > appropriate sizes.
> 
> Is it guarnteed that the page is never called on tail page?

I think so.  page_mkwrite_check_truncate() is only called on pages
which belong to a particular filesystem.  Only filesystems which have
the FS_LARGE_PAGES flag set will have compound pages allocated in the
page cache for their files.  As filesystems are converted, they will
only see large head pages.

I'll happily put in a VM_BUG_ON(PageTail(page), page); to ensure we
don't screw that up.

Patch
diff mbox series

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index aa925295347c..2ec33aabdbf6 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -732,17 +732,18 @@  static inline int page_mkwrite_check_truncate(struct page *page,
 					      struct inode *inode)
 {
 	loff_t size = i_size_read(inode);
-	pgoff_t index = size >> PAGE_SHIFT;
-	int offset = offset_in_page(size);
+	pgoff_t first_index = size >> PAGE_SHIFT;
+	pgoff_t last_index = first_index + hpage_nr_pages(page) - 1;
+	unsigned long offset = offset_in_this_page(page, size);
 
 	if (page->mapping != inode->i_mapping)
 		return -EFAULT;
 
 	/* page is wholly inside EOF */
-	if (page->index < index)
-		return PAGE_SIZE;
+	if (page->index < first_index)
+		return thp_size(page);
 	/* page is wholly past EOF */
-	if (page->index > index || !offset)
+	if (page->index > last_index || !offset)
 		return -EFAULT;
 	/* page is partially inside EOF */
 	return offset;