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 <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

fs/configfs/inode.c

···
 
 static struct backing_dev_info configfs_backing_dev_info = {
 	.ra_pages	= 0,	/* No readahead */
-	.capabilities	= BDI_CAP_NO_ACCT_DIRTY | BDI_CAP_NO_WRITEBACK,
+	.capabilities	= BDI_CAP_NO_ACCT_AND_WRITEBACK,
 };
 
 static const struct inode_operations configfs_inode_operations ={

fs/hugetlbfs/inode.c

···
 
 static struct backing_dev_info hugetlbfs_backing_dev_info = {
 	.ra_pages	= 0,	/* No readahead */
-	.capabilities	= BDI_CAP_NO_ACCT_DIRTY | BDI_CAP_NO_WRITEBACK,
+	.capabilities	= BDI_CAP_NO_ACCT_AND_WRITEBACK,
 };
 
 int sysctl_hugetlb_shm_group;

fs/ocfs2/dlm/dlmfs.c

···
 
 static struct backing_dev_info dlmfs_backing_dev_info = {
 	.ra_pages	= 0,	/* No readahead */
-	.capabilities	= BDI_CAP_NO_ACCT_DIRTY | BDI_CAP_NO_WRITEBACK,
+	.capabilities	= BDI_CAP_NO_ACCT_AND_WRITEBACK,
 };
 
 static struct inode *dlmfs_get_root_inode(struct super_block *sb)

fs/ramfs/inode.c

···
 
 static struct backing_dev_info ramfs_backing_dev_info = {
 	.ra_pages	= 0,	/* No readahead */
-	.capabilities	= BDI_CAP_NO_ACCT_DIRTY | BDI_CAP_NO_WRITEBACK |
+	.capabilities	= BDI_CAP_NO_ACCT_AND_WRITEBACK |
 			  BDI_CAP_MAP_DIRECT | BDI_CAP_MAP_COPY |
 			  BDI_CAP_READ_MAP | BDI_CAP_WRITE_MAP | BDI_CAP_EXEC_MAP,
 };

fs/sysfs/inode.c

···
 
 static struct backing_dev_info sysfs_backing_dev_info = {
 	.ra_pages	= 0,	/* No readahead */
-	.capabilities	= BDI_CAP_NO_ACCT_DIRTY | BDI_CAP_NO_WRITEBACK,
+	.capabilities	= BDI_CAP_NO_ACCT_AND_WRITEBACK,
 };
 
 static const struct inode_operations sysfs_inode_operations ={

include/linux/backing-dev.h

···
 #include <linux/log2.h>
 #include <linux/proportions.h>
 #include <linux/kernel.h>
+#include <linux/fs.h>
 #include <asm/atomic.h>
 
 struct page;
···
 
 /*
  * 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 || \
···
 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);
+}
 
-#define mapping_cap_writeback_dirty(mapping) \
-	bdi_cap_writeback_dirty((mapping)->backing_dev_info)
+static inline bool bdi_cap_account_dirty(struct backing_dev_info *bdi)
+{
+	return !(bdi->capabilities & BDI_CAP_NO_ACCT_DIRTY);
+}
 
-#define mapping_cap_account_dirty(mapping) \
-	bdi_cap_account_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));
+}
 
+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 */

kernel/cgroup.c

···
 static struct file_operations proc_cgroupstats_operations;
 
 static struct backing_dev_info cgroup_backing_dev_info = {
-	.capabilities	= BDI_CAP_NO_ACCT_DIRTY | BDI_CAP_NO_WRITEBACK,
+	.capabilities	= BDI_CAP_NO_ACCT_AND_WRITEBACK,
 };
 
 static struct inode *cgroup_new_inode(mode_t mode, struct super_block *sb)

mm/page-writeback.c

···
 			radix_tree_tag_clear(&mapping->page_tree,
 						page_index(page),
 						PAGECACHE_TAG_WRITEBACK);
-			if (bdi_cap_writeback_dirty(bdi)) {
+			if (bdi_cap_account_writeback(bdi)) {
 				__dec_bdi_stat(bdi, BDI_WRITEBACK);
 				__bdi_writeout_inc(bdi);
 			}
···
 			radix_tree_tag_set(&mapping->page_tree,
 						page_index(page),
 						PAGECACHE_TAG_WRITEBACK);
-			if (bdi_cap_writeback_dirty(bdi))
+			if (bdi_cap_account_writeback(bdi))
 				__inc_bdi_stat(bdi, BDI_WRITEBACK);
 		}
 		if (!PageDirty(page))

mm/shmem.c

···
 
 static struct backing_dev_info shmem_backing_dev_info  __read_mostly = {
 	.ra_pages	= 0,	/* No readahead */
-	.capabilities	= BDI_CAP_NO_ACCT_DIRTY | BDI_CAP_NO_WRITEBACK,
+	.capabilities	= BDI_CAP_NO_ACCT_AND_WRITEBACK,
 	.unplug_io_fn	= default_unplug_io_fn,
 };
 

mm/swap_state.c

···
 };
 
 static struct backing_dev_info swap_backing_dev_info = {
-	.capabilities	= BDI_CAP_NO_ACCT_DIRTY | BDI_CAP_NO_WRITEBACK,
+	.capabilities	= BDI_CAP_NO_ACCT_AND_WRITEBACK,
 	.unplug_io_fn	= swap_unplug_io_fn,
 };