[PATCH v13 012/137] mm: Handle per-folio private data

Matthew Wilcox (Oracle)
2021-07-12T03:15:49Z

Add folio_get_private() which mirrors page_private() -- ie folio private
data is the same as page private data. The only difference is that these
return a void * instead of an unsigned long, which matches the majority
of users.

Turn attach_page_private() into folio_attach_private() and reimplement
attach_page_private() as a wrapper. No filesystem which uses page private
data currently supports compound pages, so we're free to define the rules.
attach_page_private() may only be called on a head page; if you want
to add private data to a tail page, you can call set_page_private()
directly (and shouldn't increment the page refcount! That should be
done when adding private data to the head page / folio).

This saves 813 bytes of text with the distro-derived config that I'm
testing due to removing the calls to compound_head() in get_page()
& put_page().

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Acked-by: Jeff Layton <jlayton@kernel.org>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
Reviewed-by: David Howells <dhowells@redhat.com>
---
include/linux/mm_types.h | 11 +++++++++
include/linux/pagemap.h | 48 ++++++++++++++++++++++++----------------
2 files changed, 40 insertions(+), 19 deletions(-)

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 7a11b25cf50f..c15b4af8ef4d 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -309,6 +309,12 @@ static inline atomic_t *compound_pincount_ptr(struct page *page)
#define PAGE_FRAG_CACHE_MAX_SIZE __ALIGN_MASK(32768, ~PAGE_MASK)
#define PAGE_FRAG_CACHE_MAX_ORDER get_order(PAGE_FRAG_CACHE_MAX_SIZE)

+/*
+ * page_private can be used on tail pages. However, PagePrivate is only
+ * checked by the VM on the head page. So page_private on the tail pages
+ * should be used for data that's ancillary to the head page (eg attaching
+ * buffer heads to tail pages after attaching buffer heads to the head page)
+ */
#define page_private(page) ((page)->private)

static inline void set_page_private(struct page *page, unsigned long private)
@@ -316,6 +322,11 @@ static inline void set_page_private(struct page *page, unsigned long private)
page->private = private;
}

+static inline void *folio_get_private(struct folio *folio)
+{
+ return folio->private;
+}
+
struct page_frag_cache {
void * va;
#if (PAGE_SIZE < PAGE_FRAG_CACHE_MAX_SIZE)
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index db1726b1bc1c..df18df0ab01b 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -184,42 +184,52 @@ static inline bool page_cache_get_speculative(struct page *page)
}

/**
- * attach_page_private - Attach private data to a page.
- * @page: Page to attach data to.
- * @data: Data to attach to page.
+ * folio_attach_private - Attach private data to a folio.
+ * @folio: Folio to attach data to.
+ * @data: Data to attach to folio.
*
- * Attaching private data to a page increments the page's reference count.
- * The data must be detached before the page will be freed.
+ * Attaching private data to a folio increments the page's reference count.
+ * The data must be detached before the folio will be freed.
*/
-static inline void attach_page_private(struct page *page, void *data)
+static inline void folio_attach_private(struct folio *folio, void *data)
{
- get_page(page);
- set_page_private(page, (unsigned long)data);
- SetPagePrivate(page);
+ folio_get(folio);
+ folio->private = data;
+ folio_set_private_flag(folio);
}

/**
- * detach_page_private - Detach private data from a page.
- * @page: Page to detach data from.
+ * folio_detach_private - Detach private data from a folio.
+ * @folio: Folio to detach data from.
*
- * Removes the data that was previously attached to the page and decrements
+ * Removes the data that was previously attached to the folio and decrements
* the refcount on the page.
*
- * Return: Data that was attached to the page.
+ * Return: Data that was attached to the folio.
*/
-static inline void *detach_page_private(struct page *page)
+static inline void *folio_detach_private(struct folio *folio)
{
- void *data = (void *)page_private(page);
+ void *data = folio_get_private(folio);

- if (!PagePrivate(page))
+ if (!folio_private(folio))
return NULL;
- ClearPagePrivate(page);
- set_page_private(page, 0);
- put_page(page);
+ folio_clear_private_flag(folio);
+ folio->private = NULL;
+ folio_put(folio);

return data;
}

+static inline void attach_page_private(struct page *page, void *data)
+{
+ folio_attach_private(page_folio(page), data);
+}
+
+static inline void *detach_page_private(struct page *page)
+{
+ return folio_detach_private(page_folio(page));
+}
+
#ifdef CONFIG_NUMA
extern struct page *__page_cache_alloc(gfp_t gfp);
#else
--
2.30.2