mm: bdi: add separate writeback accounting capability

Add a new BDI capability flag: BDI_CAP_NO_ACCT_WB.  If this flag is
set, then don't update the per-bdi writeback stats from
test_set_page_writeback() and test_clear_page_writeback().

Misc cleanups:

 - convert bdi_cap_writeback_dirty() and friends to static inline functions
 - create a flag that includes all three dirty/writeback related flags,
   since almst all users will want to have them toghether

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 57 insertions, 20 deletions

diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index c49a2d045e11..13ab79d99268 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -12,6 +12,7 @@
 #include <linux/log2.h>
 #include <linux/proportions.h>
 #include <linux/kernel.h>
+#include <linux/fs.h>
 #include <asm/atomic.h>
 
 struct page;
@@ -151,22 +152,43 @@ int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned int max_ratio);
 
 /*
  * Flags in backing_dev_info::capability
- * - The first two flags control whether dirty pages will contribute to the
- *   VM's accounting and whether writepages() should be called for dirty pages
- *   (something that would not, for example, be appropriate for ramfs)
- * - These flags let !MMU mmap() govern direct device mapping vs immediate
- *   copying more easily for MAP_PRIVATE, especially for ROM filesystems
+ *
+ * The first three flags control whether dirty pages will contribute to the
+ * VM's accounting and whether writepages() should be called for dirty pages
+ * (something that would not, for example, be appropriate for ramfs)
+ *
+ * WARNING: these flags are closely related and should not normally be
+ * used separately.  The BDI_CAP_NO_ACCT_AND_WRITEBACK combines these
+ * three flags into a single convenience macro.
+ *
+ * BDI_CAP_NO_ACCT_DIRTY:  Dirty pages shouldn't contribute to accounting
+ * BDI_CAP_NO_WRITEBACK:   Don't write pages back
+ * BDI_CAP_NO_ACCT_WB:     Don't automatically account writeback pages
+ *
+ * These flags let !MMU mmap() govern direct device mapping vs immediate
+ * copying more easily for MAP_PRIVATE, especially for ROM filesystems.
+ *
+ * BDI_CAP_MAP_COPY:       Copy can be mapped (MAP_PRIVATE)
+ * BDI_CAP_MAP_DIRECT:     Can be mapped directly (MAP_SHARED)
+ * BDI_CAP_READ_MAP:       Can be mapped for reading
+ * BDI_CAP_WRITE_MAP:      Can be mapped for writing
+ * BDI_CAP_EXEC_MAP:       Can be mapped for execution
  */
-#define BDI_CAP_NO_ACCT_DIRTY	0x00000001	/* Dirty pages shouldn't contribute to accounting */
-#define BDI_CAP_NO_WRITEBACK	0x00000002	/* Don't write pages back */
-#define BDI_CAP_MAP_COPY	0x00000004	/* Copy can be mapped (MAP_PRIVATE) */
-#define BDI_CAP_MAP_DIRECT	0x00000008	/* Can be mapped directly (MAP_SHARED) */
-#define BDI_CAP_READ_MAP	0x00000010	/* Can be mapped for reading */
-#define BDI_CAP_WRITE_MAP	0x00000020	/* Can be mapped for writing */
-#define BDI_CAP_EXEC_MAP	0x00000040	/* Can be mapped for execution */
+#define BDI_CAP_NO_ACCT_DIRTY	0x00000001
+#define BDI_CAP_NO_WRITEBACK	0x00000002
+#define BDI_CAP_MAP_COPY	0x00000004
+#define BDI_CAP_MAP_DIRECT	0x00000008
+#define BDI_CAP_READ_MAP	0x00000010
+#define BDI_CAP_WRITE_MAP	0x00000020
+#define BDI_CAP_EXEC_MAP	0x00000040
+#define BDI_CAP_NO_ACCT_WB	0x00000080
+
 #define BDI_CAP_VMFLAGS \
 	(BDI_CAP_READ_MAP | BDI_CAP_WRITE_MAP | BDI_CAP_EXEC_MAP)
 
+#define BDI_CAP_NO_ACCT_AND_WRITEBACK \
+	(BDI_CAP_NO_WRITEBACK | BDI_CAP_NO_ACCT_DIRTY | BDI_CAP_NO_ACCT_WB)
+
 #if defined(VM_MAYREAD) && \
 	(BDI_CAP_READ_MAP != VM_MAYREAD || \
 	 BDI_CAP_WRITE_MAP != VM_MAYWRITE || \
@@ -206,17 +228,32 @@ void clear_bdi_congested(struct backing_dev_info *bdi, int rw);
 void set_bdi_congested(struct backing_dev_info *bdi, int rw);
 long congestion_wait(int rw, long timeout);
 
-#define bdi_cap_writeback_dirty(bdi) \
-	(!((bdi)->capabilities & BDI_CAP_NO_WRITEBACK))
 
-#define bdi_cap_account_dirty(bdi) \
-	(!((bdi)->capabilities & BDI_CAP_NO_ACCT_DIRTY))
+static inline bool bdi_cap_writeback_dirty(struct backing_dev_info *bdi)
+{
+	return !(bdi->capabilities & BDI_CAP_NO_WRITEBACK);
+}
+
+static inline bool bdi_cap_account_dirty(struct backing_dev_info *bdi)
+{
+	return !(bdi->capabilities & BDI_CAP_NO_ACCT_DIRTY);
+}
 
-#define mapping_cap_writeback_dirty(mapping) \
-	bdi_cap_writeback_dirty((mapping)->backing_dev_info)
+static inline bool bdi_cap_account_writeback(struct backing_dev_info *bdi)
+{
+	/* Paranoia: BDI_CAP_NO_WRITEBACK implies BDI_CAP_NO_ACCT_WB */
+	return !(bdi->capabilities & (BDI_CAP_NO_ACCT_WB |
+				      BDI_CAP_NO_WRITEBACK));
+}
 
-#define mapping_cap_account_dirty(mapping) \
-	bdi_cap_account_dirty((mapping)->backing_dev_info)
+static inline bool mapping_cap_writeback_dirty(struct address_space *mapping)
+{
+	return bdi_cap_writeback_dirty(mapping->backing_dev_info);
+}
 
+static inline bool mapping_cap_account_dirty(struct address_space *mapping)
+{
+	return bdi_cap_account_dirty(mapping->backing_dev_info);
+}
 
 #endif		/* _LINUX_BACKING_DEV_H */