[RESEND][PATCH 5/6] Provide a filesystem-specific sync'able page bit

[David Howells <dhowells@redhat.com>]

Because Christoph asked so nicely, I'm resending this patch with a wider
distribution. The patch currently resides in the -mm kernels. It is being used
by the in-kernel AFS filesystem and by the NFS caching patches that haven't
yet been passed to akpm.

---

The attached patch provides a filesystem-specific page bit that a filesystem
can synchronise upon. This can be used, for example, by a netfs to synchronise
with CacheFS writing its pages to disc.

Signed-Off-By: David Howells <dhowells@redhat.com>
---

warthog>diffstat cachefs-pagefsmisc-269rc1mm2.diff 
 include/linux/page-flags.h |   10 ++++++++++
 include/linux/pagemap.h    |   11 +++++++++++
 mm/filemap.c               |   17 +++++++++++++++++
 3 files changed, 38 insertions(+)

diff -uNrp linux-2.6.9-rc1-mm2/include/linux/page-flags.h linux-2.6.9-rc1-mm2-cachefs/include/linux/page-flags.h
--- linux-2.6.9-rc1-mm2/include/linux/page-flags.h	2004-08-31 16:52:38.000000000 +0100
+++ linux-2.6.9-rc1-mm2-cachefs/include/linux/page-flags.h	2004-09-02 15:15:42.000000000 +0100
@@ -62,6 +62,7 @@
 #define PG_slab			 7	/* slab debug (Suparna wants this) */
 
 #define PG_highmem		 8
+#define PG_fs_misc		 9	/* Filesystem specific bit */
 #define PG_checked		 9	/* kill me in 2.5.<early>. */
 #define PG_arch_1		10
 #define PG_reserved		11
@@ -315,4 +316,13 @@ static inline void set_page_writeback(st
 	test_set_page_writeback(page);
 }
 
+/*
+ * Filesystem-specific page bit testing
+ */
+#define PageFsMisc(page)		test_bit(PG_fs_misc, &(page)->flags)
+#define SetPageFsMisc(page)		set_bit(PG_fs_misc, &(page)->flags)
+#define TestSetPageFsMisc(page)		test_and_set_bit(PG_fs_misc, &(page)->flags)
+#define ClearPageFsMisc(page)		clear_bit(PG_fs_misc, &(page)->flags)
+#define TestClearPageFsMisc(page)	test_and_clear_bit(PG_fs_misc, &(page)->flags)
+
 #endif	/* PAGE_FLAGS_H */
diff -uNrp linux-2.6.9-rc1-mm2/include/linux/pagemap.h linux-2.6.9-rc1-mm2-cachefs/include/linux/pagemap.h
--- linux-2.6.9-rc1-mm2/include/linux/pagemap.h	2004-08-31 16:52:38.000000000 +0100
+++ linux-2.6.9-rc1-mm2-cachefs/include/linux/pagemap.h	2004-09-02 15:17:26.000000000 +0100
@@ -192,6 +192,17 @@ static inline void wait_on_page_writebac
 extern void end_page_writeback(struct page *page);
 
 /*
+ * Wait for filesystem-specific page synchronisation to complete
+ */
+static inline void wait_on_page_fs_misc(struct page *page)
+{
+	if (PageFsMisc(page))
+		wait_on_page_bit(page, PG_fs_misc);
+}
+
+extern void fastcall end_page_fs_misc(struct page *page);
+
+/*
  * Fault a userspace page into pagetables.  Return non-zero on a fault.
  *
  * This assumes that two userspace pages are always sufficient.  That's
diff -uNrp linux-2.6.9-rc1-mm2/mm/filemap.c linux-2.6.9-rc1-mm2-cachefs/mm/filemap.c
--- linux-2.6.9-rc1-mm2/mm/filemap.c	2004-08-31 16:52:40.000000000 +0100
+++ linux-2.6.9-rc1-mm2-cachefs/mm/filemap.c	2004-09-03 16:46:58.780545691 +0100
@@ -442,6 +442,23 @@ void fastcall __lock_page(struct page *p
 EXPORT_SYMBOL(__lock_page);
 
 /*
+ * Note completion of filesystem specific page synchronisation
+ *
+ * This is used to allow a page to be written to a filesystem cache in the
+ * background without holding up the completion of readpage
+ */
+void fastcall end_page_fs_misc(struct page *page)
+{
+	smp_mb__before_clear_bit();
+	if (!TestClearPageFsMisc(page))
+		BUG();
+	smp_mb__after_clear_bit(); 
+	wake_up_page(page, PG_fs_misc);
+}
+
+EXPORT_SYMBOL(end_page_fs_misc);
+
+/*
  * a rather lightweight function, finding and getting a reference to a
  * hashed page atomically.
  */