[PATCH] laptop-mode: Make flushes per-device

[Matthew Garrett <mjg@redhat.com>]

One of the features of laptop-mode is that it forces a writeout of dirty
pages if something else triggers a physical read or write from a device.
The current implementation flushes pages on all devices, rather than only
the one that triggered the flush. This patch alters the behaviour so that
only the recently accessed block device is flushed, preventing other
disks being spun up for no terribly good reason.

Signed-off-by: Matthew Garrett <mjg@redhat.com>
---
 block/blk-core.c            |    6 ++++-
 include/linux/backing-dev.h |    4 +++
 include/linux/writeback.h   |    5 +++-
 mm/page-writeback.c         |   44 ++++++++++++++++++++++++++----------------
 4 files changed, 40 insertions(+), 19 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index 718897e..64e9b05 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -510,10 +510,14 @@ struct request_queue *blk_alloc_queue_node(gfp_t gfp_mask, int node_id)
 		return NULL;
 	}
 
+	init_timer(&q->backing_dev_info.laptop_mode_wb_timer);
+	setup_timer(&q->backing_dev_info.laptop_mode_wb_timer,
+		    laptop_mode_timer_fn, (unsigned long) q);
 	init_timer(&q->unplug_timer);
 	setup_timer(&q->timeout, blk_rq_timed_out_timer, (unsigned long) q);
 	INIT_LIST_HEAD(&q->timeout_list);
 	INIT_WORK(&q->unplug_work, blk_unplug_work);
+	INIT_WORK(&q->backing_dev_info.laptop_mode_wb_work, laptop_mode_sync);
 
 	kobject_init(&q->kobj, &blk_queue_ktype);
 
@@ -2109,7 +2113,7 @@ static void blk_finish_request(struct request *req, int error)
 	BUG_ON(blk_queued_rq(req));
 
 	if (unlikely(laptop_mode) && blk_fs_request(req))
-		laptop_io_completion();
+		laptop_io_completion(req);
 
 	blk_delete_timer(req);
 
diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index fcbc26a..98fed25 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -14,6 +14,7 @@
 #include <linux/kernel.h>
 #include <linux/fs.h>
 #include <linux/sched.h>
+#include <linux/timer.h>
 #include <linux/writeback.h>
 #include <asm/atomic.h>
 
@@ -88,6 +89,9 @@ struct backing_dev_info {
 
 	struct device *dev;
 
+	struct timer_list laptop_mode_wb_timer;
+	struct work_struct laptop_mode_wb_work;
+
 #ifdef CONFIG_DEBUG_FS
 	struct dentry *debug_dir;
 	struct dentry *debug_stats;
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index 705f01f..7fdadb1 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -6,6 +6,7 @@
 
 #include <linux/sched.h>
 #include <linux/fs.h>
+#include <linux/blkdev.h>
 
 struct backing_dev_info;
 
@@ -93,8 +94,10 @@ static inline void inode_sync_wait(struct inode *inode)
 /*
  * mm/page-writeback.c
  */
-void laptop_io_completion(void);
+void laptop_io_completion(struct request *req);
 void laptop_sync_completion(void);
+void laptop_mode_sync(struct work_struct *work);
+void laptop_mode_timer_fn(unsigned long data);
 void throttle_vm_writeout(gfp_t gfp_mask);
 
 /* These are exported to sysctl. */
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 0b19943..9b62ebe 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -683,10 +683,6 @@ void throttle_vm_writeout(gfp_t gfp_mask)
         }
 }
 
-static void laptop_timer_fn(unsigned long unused);
-
-static DEFINE_TIMER(laptop_mode_wb_timer, laptop_timer_fn, 0, 0);
-
 /*
  * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
  */
@@ -697,21 +693,27 @@ int dirty_writeback_centisecs_handler(ctl_table *table, int write,
 	return 0;
 }
 
-static void do_laptop_sync(struct work_struct *work)
+void laptop_mode_sync(struct work_struct *work)
 {
-	wakeup_flusher_threads(0);
-	kfree(work);
+	struct backing_dev_info *bdi =
+		container_of(work, struct backing_dev_info,
+			     laptop_mode_wb_work);
+	int nr_pages = global_page_state(NR_FILE_DIRTY) +
+		global_page_state(NR_UNSTABLE_NFS);
+
+	/*
+	 * We want to write everything out, not just down to the dirty
+	 * threshold
+	 */
+	if (bdi_has_dirty_io(bdi))
+		bdi_start_writeback(bdi, NULL, nr_pages);
 }
 
-static void laptop_timer_fn(unsigned long unused)
+void laptop_mode_timer_fn(unsigned long data)
 {
-	struct work_struct *work;
+	struct request_queue *q = (struct request_queue *)data;
 
-	work = kmalloc(sizeof(*work), GFP_ATOMIC);
-	if (work) {
-		INIT_WORK(work, do_laptop_sync);
-		schedule_work(work);
-	}
+	schedule_work(&q->backing_dev_info.laptop_mode_wb_work);
 }
 
 /*
@@ -719,9 +721,10 @@ static void laptop_timer_fn(unsigned long unused)
  * of all dirty data a few seconds from now.  If the flush is already scheduled
  * then push it back - the user is still using the disk.
  */
-void laptop_io_completion(void)
+void laptop_io_completion(struct request *req)
 {
-	mod_timer(&laptop_mode_wb_timer, jiffies + laptop_mode);
+	mod_timer(&req->q->backing_dev_info.laptop_mode_wb_timer,
+		  jiffies + laptop_mode);
 }
 
 /*
@@ -731,7 +734,14 @@ void laptop_io_completion(void)
  */
 void laptop_sync_completion(void)
 {
-	del_timer(&laptop_mode_wb_timer);
+	struct backing_dev_info *bdi;
+
+	rcu_read_lock();
+
+	list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
+		del_timer(&bdi->laptop_mode_wb_timer);
+
+	rcu_read_unlock();
 }
 
 /*
-- 
1.6.5.2