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Subject[PATCH 1/7] FS-Cache: Provide a filesystem-specific sync'able page bit
Date
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 disk.

Signed-Off-By: David Howells <dhowells@redhat.com>
---
include/linux/page-flags.h | 10 ++++++++++
include/linux/pagemap.h | 11 +++++++++++
mm/filemap.c | 17 +++++++++++++++++
3 files changed, 38 insertions(+), 0 deletions(-)
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index d276a4e..5486874 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -74,6 +74,7 @@
#define PG_slab 7 /* slab debug (Suparna wants this) */

#define PG_checked 8 /* kill me in 2.5.<early>. */
+#define PG_fs_misc 8
#define PG_arch_1 9
#define PG_reserved 10
#define PG_private 11 /* Has something at ->private */
@@ -376,4 +377,13 @@ 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 --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 9539efd..02e7d8b 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -206,6 +206,17 @@ 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 --git a/mm/filemap.c b/mm/filemap.c
index 3ef2073..d4a598f 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -545,6 +545,23 @@ 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_bit(page_waitqueue(page), &page->flags, PG_fs_misc);
+}
+
+EXPORT_SYMBOL(end_page_fs_misc);
+
+/*
* a rather lightweight function, finding and getting a reference to a
* hashed page atomically.
*/
-
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