[PATCH v13 031/137] fs/netfs: Add folio fscache functions

Matthew Wilcox (Oracle)
2021-07-12T03:25:00Z

Match the page writeback functions by adding
folio_start_fscache(), folio_end_fscache(), folio_wait_fscache() and
folio_wait_fscache_killable(). Remove set_page_private_2(). Also rewrite
the kernel-doc to describe when to use the function rather than what the
function does, and include the kernel-doc in the appropriate rst file.
Saves 31 bytes of text in netfs_rreq_unlock() due to set_page_fscache()
calling page_folio() once instead of three times.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
Documentation/filesystems/netfs_library.rst | 2 +
include/linux/netfs.h | 75 +++++++++++++--------
include/linux/pagemap.h | 16 -----
3 files changed, 50 insertions(+), 43 deletions(-)

diff --git a/Documentation/filesystems/netfs_library.rst b/Documentation/filesystems/netfs_library.rst
index 57a641847818..bb68d39f03b7 100644
--- a/Documentation/filesystems/netfs_library.rst
+++ b/Documentation/filesystems/netfs_library.rst
@@ -524,3 +524,5 @@ Note that these methods are passed a pointer to the cache resource structure,
not the read request structure as they could be used in other situations where
there isn't a read request structure as well, such as writing dirty data to the
cache.
+
+.. kernel-doc:: include/linux/netfs.h
diff --git a/include/linux/netfs.h b/include/linux/netfs.h
index fad8c6209edd..91098e61b4eb 100644
--- a/include/linux/netfs.h
+++ b/include/linux/netfs.h
@@ -22,6 +22,7 @@
* Overload PG_private_2 to give us PG_fscache - this is used to indicate that
* a page is currently backed by a local disk cache
*/
+#define folio_fscache(folio) folio_private_2(folio)
#define PageFsCache(page) PagePrivate2((page))
#define SetPageFsCache(page) SetPagePrivate2((page))
#define ClearPageFsCache(page) ClearPagePrivate2((page))
@@ -29,57 +30,77 @@
#define TestClearPageFsCache(page) TestClearPagePrivate2((page))

/**
- * set_page_fscache - Set PG_fscache on a page and take a ref
- * @page: The page.
+ * folio_start_fscache - Start an fscache write on a folio.
+ * @folio: The folio.
*
- * Set the PG_fscache (PG_private_2) flag on a page and take the reference
- * needed for the VM to handle its lifetime correctly. This sets the flag and
- * takes the reference unconditionally, so care must be taken not to set the
- * flag again if it's already set.
+ * Call this function before writing a folio to a local cache. Starting a
+ * second write before the first one finishes is not allowed.
*/
-static inline void set_page_fscache(struct page *page)
+static inline void folio_start_fscache(struct folio *folio)
{
- set_page_private_2(page);
+ VM_BUG_ON_FOLIO(folio_private_2(folio), folio);
+ folio_get(folio);
+ folio_set_private_2_flag(folio);
}

/**
- * end_page_fscache - Clear PG_fscache and release any waiters
- * @page: The page
- *
- * Clear the PG_fscache (PG_private_2) bit on a page and wake up any sleepers
- * waiting for this. The page ref held for PG_private_2 being set is released.
+ * folio_end_fscache - End an fscache write on a folio.
+ * @folio: The folio.
*
- * This is, for example, used when a netfs page is being written to a local
- * disk cache, thereby allowing writes to the cache for the same page to be
- * serialised.
+ * Call this function after the folio has been written to the local cache.
+ * This will wake any sleepers waiting on this folio.
*/
-static inline void end_page_fscache(struct page *page)
+static inline void folio_end_fscache(struct folio *folio)
{
- folio_end_private_2(page_folio(page));
+ folio_end_private_2(folio);
}

/**
- * wait_on_page_fscache - Wait for PG_fscache to be cleared on a page
- * @page: The page to wait on
+ * folio_wait_fscache - Wait for an fscache write on this folio to end.
+ * @folio: The folio.
*
- * Wait for PG_fscache (aka PG_private_2) to be cleared on a page.
+ * If this folio is currently being written to a local cache, wait for
+ * the write to finish. Another write may start after this one finishes,
+ * unless the caller holds the folio lock.
*/
-static inline void wait_on_page_fscache(struct page *page)
+static inline void folio_wait_fscache(struct folio *folio)
{
- folio_wait_private_2(page_folio(page));
+ folio_wait_private_2(folio);
}

/**
- * wait_on_page_fscache_killable - Wait for PG_fscache to be cleared on a page
- * @page: The page to wait on
+ * folio_wait_fscache_killable - Wait for an fscache write on this folio to end.
+ * @folio: The folio.
*
- * Wait for PG_fscache (aka PG_private_2) to be cleared on a page or until a
- * fatal signal is received by the calling task.
+ * If this folio is currently being written to a local cache, wait
+ * for the write to finish or for a fatal signal to be received.
+ * Another write may start after this one finishes, unless the caller
+ * holds the folio lock.
*
* Return:
* - 0 if successful.
* - -EINTR if a fatal signal was encountered.
*/
+static inline int folio_wait_fscache_killable(struct folio *folio)
+{
+ return folio_wait_private_2_killable(folio);
+}
+
+static inline void set_page_fscache(struct page *page)
+{
+ folio_start_fscache(page_folio(page));
+}
+
+static inline void end_page_fscache(struct page *page)
+{
+ folio_end_private_2(page_folio(page));
+}
+
+static inline void wait_on_page_fscache(struct page *page)
+{
+ folio_wait_private_2(page_folio(page));
+}
+
static inline int wait_on_page_fscache_killable(struct page *page)
{
return folio_wait_private_2_killable(page_folio(page));
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index dfbb23acecae..00bd9032418d 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -780,22 +780,6 @@ int __set_page_dirty_no_writeback(struct page *page);

void page_endio(struct page *page, bool is_write, int err);

-/**
- * set_page_private_2 - Set PG_private_2 on a page and take a ref
- * @page: The page.
- *
- * Set the PG_private_2 flag on a page and take the reference needed for the VM
- * to handle its lifetime correctly. This sets the flag and takes the
- * reference unconditionally, so care must be taken not to set the flag again
- * if it's already set.
- */
-static inline void set_page_private_2(struct page *page)
-{
- page = compound_head(page);
- get_page(page);
- SetPagePrivate2(page);
-}
-
void folio_end_private_2(struct folio *folio);
void folio_wait_private_2(struct folio *folio);
int folio_wait_private_2_killable(struct folio *folio);
--
2.30.2