[PATCH] remove PF_SYNC

current->flags:PF_SYNC was a hack I added because I didn't want to
change all ->writepage implementations.

It's foul.  And it means that if someone happens to run direct page
reclaim within the context of (say) sys_sync, the writepage invokations
from the VM will be treated as "data integrity" operations, not "memory
cleansing" operations, which would cause latency.

So the patch removes PF_SYNC and adds an extra arg to a_ops->writepage.
 It is the `writeback_control' structure which contains the full context
information about why writepage was called.

The initial version of this patch just passed in a bare `int sync', but
the XFS team need more info so they can perform writearound from within
page reclaim.

The patch also adds writeback_control.for_reclaim, so writepage
implementations can inspect that to work out the call context rather
than peeking at current->flags:PF_MEMALLOC.

6 files changed, 8 insertions, 16 deletions

diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
index 4e7a9bbf99dd..e9d6251fa168 100644
--- a/include/linux/buffer_head.h
+++ b/include/linux/buffer_head.h
@@ -178,7 +178,7 @@ extern int buffer_heads_over_limit;
  */
 int try_to_release_page(struct page * page, int gfp_mask);
 int block_invalidatepage(struct page *page, unsigned long offset);
-int block_write_full_page(struct page*, get_block_t*);
+int block_write_full_page(struct page *page, get_block_t *get_block, struct writeback_control *wbc);
 int block_read_full_page(struct page*, get_block_t*);
 int block_prepare_write(struct page*, unsigned, unsigned, get_block_t*);
 int cont_prepare_write(struct page*, unsigned, unsigned, get_block_t*,
diff --git a/include/linux/fs.h b/include/linux/fs.h
index afbb9474f25b..bd133801c3e0 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -278,7 +278,7 @@ struct address_space;
 struct writeback_control;
 
 struct address_space_operations {
-	int (*writepage)(struct page *);
+	int (*writepage)(struct page *page, struct writeback_control *wbc);
 	int (*readpage)(struct file *, struct page *);
 	int (*sync_page)(struct page *);
 
diff --git a/include/linux/nfs_fs.h b/include/linux/nfs_fs.h
index 8d15e17c0b94..2673e32cc4ba 100644
--- a/include/linux/nfs_fs.h
+++ b/include/linux/nfs_fs.h
@@ -291,7 +291,7 @@ extern void nfs_complete_unlink(struct dentry *);
 /*
  * linux/fs/nfs/write.c
  */
-extern int  nfs_writepage(struct page *);
+extern int  nfs_writepage(struct page *page, struct writeback_control *wbc);
 extern int  nfs_writepages(struct address_space *, struct writeback_control *);
 extern int  nfs_flush_incompatible(struct file *file, struct page *page);
 extern int  nfs_updatepage(struct file *, struct page *, unsigned int, unsigned int);
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 80a9836df919..d0726cb87145 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -424,9 +424,8 @@ do { if (atomic_dec_and_test(&(tsk)->usage)) __put_task_struct(tsk); } while(0)
 #define PF_FREEZE	0x00008000	/* this task should be frozen for suspend */
 #define PF_IOTHREAD	0x00010000	/* this thread is needed for doing I/O to swap */
 #define PF_FROZEN	0x00020000	/* frozen for system suspend */
-#define PF_SYNC		0x00040000	/* performing fsync(), etc */
-#define PF_FSTRANS	0x00080000	/* inside a filesystem transaction */
-#define PF_KSWAPD	0x00100000	/* I am kswapd */
+#define PF_FSTRANS	0x00040000	/* inside a filesystem transaction */
+#define PF_KSWAPD	0x00080000	/* I am kswapd */
 
 /*
  * Ptrace flags
diff --git a/include/linux/swap.h b/include/linux/swap.h
index f6b1421f86b0..c635f392d6c1 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -65,6 +65,7 @@ typedef struct {
 struct sysinfo;
 struct address_space;
 struct zone;
+struct writeback_control;
 
 /*
  * A swap extent maps a range of a swapfile's PAGE_SIZE pages onto a range of
@@ -180,7 +181,7 @@ extern int shmem_unuse(swp_entry_t entry, struct page *page);
 #ifdef CONFIG_SWAP
 /* linux/mm/page_io.c */
 extern int swap_readpage(struct file *, struct page *);
-extern int swap_writepage(struct page *);
+extern int swap_writepage(struct page *page, struct writeback_control *wbc);
 extern int rw_swap_page_sync(int, swp_entry_t, struct page *);
 
 /* linux/mm/swap_state.c */
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index 351e5851c041..620f18f5ceeb 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -42,6 +42,7 @@ struct writeback_control {
 	int nonblocking;		/* Don't get stuck on request queues */
 	int encountered_congestion;	/* An output: a queue is full */
 	int for_kupdate;		/* A kupdate writeback */
+	int for_reclaim;		/* Invoked from the page allocator */
 };
 
 /*
@@ -88,13 +89,4 @@ extern int nr_pdflush_threads;	/* Global so it can be exported to sysctl
 				   read-only. */
 
 
-/*
- * Tell the writeback paths that they are being called for a "data integrity"
- * operation such as fsync().
- */
-static inline int called_for_sync(void)
-{
-	return current->flags & PF_SYNC;
-}
-
 #endif		/* WRITEBACK_H */