[v11,13/33] mm/filemap: Add folio_index(), folio_file_page() and folio_contains()

Commit Message

Matthew Wilcox (Oracle) June 14, 2021, 8:14 p.m. UTC

folio_index() is the equivalent of page_index() for folios.
folio_file_page() is the equivalent of find_subpage().
folio_contains() is the equivalent of thp_contains().

No changes to generated code.

Signed-off-by: Matthew Wilcox (Oracle) <[e-mail]>
Reviewed-by: Christoph Hellwig <[e-mail]>
Acked-by: Jeff Layton <[e-mail]>
Acked-by: Kirill A. Shutemov <[e-mail]>
Acked-by: Vlastimil Babka <[e-mail]>
Reviewed-by: William Kucharski <[e-mail]>
---
 include/linux/pagemap.h | 56 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 56 insertions(+)

Comments

David Howells June 16, 2021, 10:03 a.m. UTC | #1

Matthew Wilcox (Oracle) <[e-mail]> wrote:

> folio_index() is the equivalent of page_index() for folios.
> folio_file_page() is the equivalent of find_subpage().
> folio_contains() is the equivalent of thp_contains().
> 
> No changes to generated code.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <[e-mail]>
> Reviewed-by: Christoph Hellwig <[e-mail]>
> Acked-by: Jeff Layton <[e-mail]>
> Acked-by: Kirill A. Shutemov <[e-mail]>
> Acked-by: Vlastimil Babka <[e-mail]>
> Reviewed-by: William Kucharski <[e-mail]>

folio_subpage() might be a better name than folio_file_page().

Reviewed-by: David Howells <[e-mail]>

Matthew Wilcox (Oracle) June 16, 2021, 11:38 a.m. UTC | #2

On Wed, Jun 16, 2021 at 11:03:23AM +0100, David Howells wrote:
> Matthew Wilcox (Oracle) <[e-mail]> wrote:
> 
> > folio_index() is the equivalent of page_index() for folios.
> > folio_file_page() is the equivalent of find_subpage().
> > folio_contains() is the equivalent of thp_contains().
> > 
> > No changes to generated code.
> > 
> > Signed-off-by: Matthew Wilcox (Oracle) <[e-mail]>
> > Reviewed-by: Christoph Hellwig <[e-mail]>
> > Acked-by: Jeff Layton <[e-mail]>
> > Acked-by: Kirill A. Shutemov <[e-mail]>
> > Acked-by: Vlastimil Babka <[e-mail]>
> > Reviewed-by: William Kucharski <[e-mail]>
> 
> folio_subpage() might be a better name than folio_file_page().

I want it to be clear that you can't call this for folios which
aren't part of a file.  For example, anonymous memory.

Patch

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 91aaf3207ad0..37a4b583abad 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -386,6 +386,62 @@  static inline bool thp_contains(struct page *head, pgoff_t index)
 	return page_index(head) == (index & ~(thp_nr_pages(head) - 1UL));
 }
 
+#define swapcache_index(folio)	__page_file_index(&(folio)->page)
+
+/**
+ * folio_index - File index of a folio.
+ * @folio: The folio.
+ *
+ * For a folio which is either in the page cache or the swap cache,
+ * return its index within the address_space it belongs to.  If you know
+ * the page is definitely in the page cache, you can look at the folio's
+ * index directly.
+ *
+ * Return: The index (offset in units of pages) of a folio in its file.
+ */
+static inline pgoff_t folio_index(struct folio *folio)
+{
+        if (unlikely(folio_swapcache(folio)))
+                return swapcache_index(folio);
+        return folio->index;
+}
+
+/**
+ * folio_file_page - The page for a particular index.
+ * @folio: The folio which contains this index.
+ * @index: The index we want to look up.
+ *
+ * Sometimes after looking up a folio in the page cache, we need to
+ * obtain the specific page for an index (eg a page fault).
+ *
+ * Return: The page containing the file data for this index.
+ */
+static inline struct page *folio_file_page(struct folio *folio, pgoff_t index)
+{
+	/* HugeTLBfs indexes the page cache in units of hpage_size */
+	if (folio_hugetlb(folio))
+		return &folio->page;
+	return folio_page(folio, index & (folio_nr_pages(folio) - 1));
+}
+
+/**
+ * folio_contains - Does this folio contain this index?
+ * @folio: The folio.
+ * @index: The page index within the file.
+ *
+ * Context: The caller should have the page locked in order to prevent
+ * (eg) shmem from moving the page between the page cache and swap cache
+ * and changing its index in the middle of the operation.
+ * Return: true or false.
+ */
+static inline bool folio_contains(struct folio *folio, pgoff_t index)
+{
+	/* HugeTLBfs indexes the page cache in units of hpage_size */
+	if (folio_hugetlb(folio))
+		return folio->index == index;
+	return index - folio_index(folio) < folio_nr_pages(folio);
+}
+
 /*
  * Given the page we found in the page cache, return the page corresponding
  * to this index in the file