[PATCH 04/10] writeback: separate the flushing state/task from the bdi

From: Jens Axboe
Date: Thu Jun 25 2009 - 06:44:01 EST

Add a struct bdi_writeback for tracking and handling dirty IO. This
is in preparation for adding > 1 flusher task per bdi.

Signed-off-by: Jens Axboe <jens.axboe@xxxxxxxxxx>
---
fs/fs-writeback.c | 147 ++++++++++++++++++++++++++----------------
include/linux/backing-dev.h | 38 +++++++-----
mm/backing-dev.c | 120 ++++++++++++++++++++++++++---------
3 files changed, 204 insertions(+), 101 deletions(-)

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 7b49d90..86fb2a9 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -29,6 +29,10 @@

#define inode_to_bdi(inode) ((inode)->i_mapping->backing_dev_info)

+static void generic_sync_wb_inodes(struct bdi_writeback *wb,
+ struct super_block *sb,
+ struct writeback_control *wbc);
+
/*
* We don't actually have pdflush, but this one is exported though /proc...
*/
@@ -46,9 +50,11 @@ int nr_pdflush_threads;
* unless they implement their own. Which is somewhat inefficient, as this
* may prevent concurrent writeback against multiple devices.
*/
-static int writeback_acquire(struct backing_dev_info *bdi)
+static int writeback_acquire(struct bdi_writeback *wb)
{
- return !test_and_set_bit(BDI_pdflush, &bdi->state);
+ struct backing_dev_info *bdi = wb->bdi;
+
+ return !test_and_set_bit(wb->nr, &bdi->wb_active);
}

/**
@@ -59,19 +65,37 @@ static int writeback_acquire(struct backing_dev_info *bdi)
*/
int writeback_in_progress(struct backing_dev_info *bdi)
{
- return test_bit(BDI_pdflush, &bdi->state);
+ return bdi->wb_active != 0;
}

/**
* writeback_release - relinquish exclusive writeback access against a device.
* @bdi: the device's backing_dev_info structure
*/
-static void writeback_release(struct backing_dev_info *bdi)
+static void writeback_release(struct bdi_writeback *wb)
+{
+ struct backing_dev_info *bdi = wb->bdi;
+
+ wb->nr_pages = 0;
+ wb->sb = NULL;
+ clear_bit(wb->nr, &bdi->wb_active);
+}
+
+static void wb_start_writeback(struct bdi_writeback *wb, struct super_block *sb,
+ long nr_pages,
+ enum writeback_sync_modes sync_mode)
{
- WARN_ON_ONCE(!writeback_in_progress(bdi));
- bdi->wb_arg.nr_pages = 0;
- bdi->wb_arg.sb = NULL;
- clear_bit(BDI_pdflush, &bdi->state);
+ if (!wb_has_dirty_io(wb))
+ return;
+
+ if (writeback_acquire(wb)) {
+ wb->nr_pages = nr_pages;
+ wb->sb = sb;
+ wb->sync_mode = sync_mode;
+
+ if (wb->task)
+ wake_up_process(wb->task);
+ }
}

void bdi_start_writeback(struct backing_dev_info *bdi, struct super_block *sb,
@@ -81,17 +105,10 @@ void bdi_start_writeback(struct backing_dev_info *bdi, struct super_block *sb,
* This only happens the first time someone kicks this bdi, so put
* it out-of-line.
*/
- if (unlikely(!bdi->task))
- wake_up_process(default_backing_dev_info.task);
+ if (unlikely(!bdi->wb.task))
+ wake_up_process(default_backing_dev_info.wb.task);

- if (writeback_acquire(bdi)) {
- bdi->wb_arg.nr_pages = nr_pages;
- bdi->wb_arg.sb = sb;
- bdi->wb_arg.sync_mode = sync_mode;
-
- if (bdi->task)
- wake_up_process(bdi->task);
- }
+ wb_start_writeback(&bdi->wb, sb, nr_pages, sync_mode);
}

/*
@@ -128,17 +145,17 @@ static inline bool over_bground_thresh(void)
* older_than_this takes precedence over nr_to_write. So we'll only write back
* all dirty pages if they are all attached to "old" mappings.
*/
-static void bdi_flush(struct backing_dev_info *bdi, int for_kupdate)
+static void wb_writeback(struct bdi_writeback *wb, int for_kupdate)
{
struct writeback_control wbc = {
- .bdi = bdi,
- .sync_mode = bdi->wb_arg.sync_mode,
+ .bdi = wb->bdi,
+ .sync_mode = wb->sync_mode,
.older_than_this = NULL,
.for_kupdate = for_kupdate,
.range_cyclic = 1,
};
unsigned long oldest_jif;
- long nr_pages = bdi->wb_arg.nr_pages;
+ long nr_pages = wb->nr_pages;

if (wbc.for_kupdate) {
wbc.older_than_this = &oldest_jif;
@@ -155,7 +172,7 @@ static void bdi_flush(struct backing_dev_info *bdi, int for_kupdate)
wbc.encountered_congestion = 0;
wbc.nr_to_write = MAX_WRITEBACK_PAGES;
wbc.pages_skipped = 0;
- generic_sync_bdi_inodes(bdi->wb_arg.sb, &wbc);
+ generic_sync_wb_inodes(wb, wb->sb, &wbc);
nr_pages -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;
/*
* If we ran out of stuff to write, bail unless more_io got set
@@ -172,17 +189,12 @@ static void bdi_flush(struct backing_dev_info *bdi, int for_kupdate)
* Handle writeback of dirty data for the device backed by this bdi. Also
* wakes up periodically and does kupdated style flushing.
*/
-int bdi_writeback_task(struct backing_dev_info *bdi)
+int bdi_writeback_task(struct bdi_writeback *wb)
{
while (!kthread_should_stop()) {
unsigned long wait_jiffies;
int for_kupdate;

- wait_jiffies = msecs_to_jiffies(dirty_writeback_interval * 10);
- set_current_state(TASK_INTERRUPTIBLE);
- schedule_timeout(wait_jiffies);
- try_to_freeze();
-
/*
* We get here in two cases:
*
@@ -197,7 +209,7 @@ int bdi_writeback_task(struct backing_dev_info *bdi)
* pdflush style writeout.
*
*/
- for_kupdate = writeback_acquire(bdi);
+ for_kupdate = writeback_acquire(wb);
if (for_kupdate) {
long nr;

@@ -205,13 +217,18 @@ int bdi_writeback_task(struct backing_dev_info *bdi)
global_page_state(NR_UNSTABLE_NFS) +
(inodes_stat.nr_inodes - inodes_stat.nr_unused);

- bdi->wb_arg.nr_pages = nr;
- bdi->wb_arg.sb = NULL;
- bdi->wb_arg.sync_mode = WB_SYNC_NONE;
+ wb->nr_pages = nr;
+ wb->sb = NULL;
+ wb->sync_mode = WB_SYNC_NONE;
}

- bdi_flush(bdi, for_kupdate);
- writeback_release(bdi);
+ wb_writeback(wb, for_kupdate);
+ writeback_release(wb);
+
+ wait_jiffies = msecs_to_jiffies(dirty_writeback_interval * 10);
+ set_current_state(TASK_INTERRUPTIBLE);
+ schedule_timeout(wait_jiffies);
+ try_to_freeze();
}

return 0;
@@ -254,6 +271,14 @@ static noinline void block_dump___mark_inode_dirty(struct inode *inode)
}
}

+/*
+ * We have only a single wb per bdi, so just return that.
+ */
+static inline struct bdi_writeback *inode_get_wb(struct inode *inode)
+{
+ return &inode_to_bdi(inode)->wb;
+}
+
/**
* __mark_inode_dirty - internal function
* @inode: inode to mark
@@ -337,9 +362,10 @@ void __mark_inode_dirty(struct inode *inode, int flags)
* reposition it (that would break b_dirty time-ordering).
*/
if (!was_dirty) {
+ struct bdi_writeback *wb = inode_get_wb(inode);
+
inode->dirtied_when = jiffies;
- list_move(&inode->i_list,
- &inode_to_bdi(inode)->b_dirty);
+ list_move(&inode->i_list, &wb->b_dirty);
}
}
out:
@@ -366,16 +392,16 @@ static int write_inode(struct inode *inode, int sync)
*/
static void redirty_tail(struct inode *inode)
{
- struct backing_dev_info *bdi = inode_to_bdi(inode);
+ struct bdi_writeback *wb = inode_get_wb(inode);

- if (!list_empty(&bdi->b_dirty)) {
+ if (!list_empty(&wb->b_dirty)) {
struct inode *tail;

- tail = list_entry(bdi->b_dirty.next, struct inode, i_list);
+ tail = list_entry(wb->b_dirty.next, struct inode, i_list);
if (time_before(inode->dirtied_when, tail->dirtied_when))
inode->dirtied_when = jiffies;
}
- list_move(&inode->i_list, &bdi->b_dirty);
+ list_move(&inode->i_list, &wb->b_dirty);
}

/*
@@ -383,7 +409,9 @@ static void redirty_tail(struct inode *inode)
*/
static void requeue_io(struct inode *inode)
{
- list_move(&inode->i_list, &inode_to_bdi(inode)->b_more_io);
+ struct bdi_writeback *wb = inode_get_wb(inode);
+
+ list_move(&inode->i_list, &wb->b_more_io);
}

static void inode_sync_complete(struct inode *inode)
@@ -430,11 +458,10 @@ static void move_expired_inodes(struct list_head *delaying_queue,
/*
* Queue all expired dirty inodes for io, eldest first.
*/
-static void queue_io(struct backing_dev_info *bdi,
- unsigned long *older_than_this)
+static void queue_io(struct bdi_writeback *wb, unsigned long *older_than_this)
{
- list_splice_init(&bdi->b_more_io, bdi->b_io.prev);
- move_expired_inodes(&bdi->b_dirty, &bdi->b_io, older_than_this);
+ list_splice_init(&wb->b_more_io, wb->b_io.prev);
+ move_expired_inodes(&wb->b_dirty, &wb->b_io, older_than_this);
}

/*
@@ -593,20 +620,20 @@ writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
return ret;
}

-void generic_sync_bdi_inodes(struct super_block *sb,
- struct writeback_control *wbc)
+static void generic_sync_wb_inodes(struct bdi_writeback *wb,
+ struct super_block *sb,
+ struct writeback_control *wbc)
{
const int is_blkdev_sb = sb_is_blkdev_sb(sb);
- struct backing_dev_info *bdi = wbc->bdi;
const unsigned long start = jiffies; /* livelock avoidance */

spin_lock(&inode_lock);

- if (!wbc->for_kupdate || list_empty(&bdi->b_io))
- queue_io(bdi, wbc->older_than_this);
+ if (!wbc->for_kupdate || list_empty(&wb->b_io))
+ queue_io(wb, wbc->older_than_this);

- while (!list_empty(&bdi->b_io)) {
- struct inode *inode = list_entry(bdi->b_io.prev,
+ while (!list_empty(&wb->b_io)) {
+ struct inode *inode = list_entry(wb->b_io.prev,
struct inode, i_list);
long pages_skipped;

@@ -618,7 +645,7 @@ void generic_sync_bdi_inodes(struct super_block *sb,
continue;
}

- if (!bdi_cap_writeback_dirty(bdi)) {
+ if (!bdi_cap_writeback_dirty(wb->bdi)) {
redirty_tail(inode);
if (is_blkdev_sb) {
/*
@@ -640,7 +667,7 @@ void generic_sync_bdi_inodes(struct super_block *sb,
continue;
}

- if (wbc->nonblocking && bdi_write_congested(bdi)) {
+ if (wbc->nonblocking && bdi_write_congested(wb->bdi)) {
wbc->encountered_congestion = 1;
if (!is_blkdev_sb)
break; /* Skip a congested fs */
@@ -674,7 +701,7 @@ void generic_sync_bdi_inodes(struct super_block *sb,
wbc->more_io = 1;
break;
}
- if (!list_empty(&bdi->b_more_io))
+ if (!list_empty(&wb->b_more_io))
wbc->more_io = 1;
}

@@ -682,6 +709,14 @@ void generic_sync_bdi_inodes(struct super_block *sb,
/* Leave any unwritten inodes on b_io */
}

+void generic_sync_bdi_inodes(struct super_block *sb,
+ struct writeback_control *wbc)
+{
+ struct backing_dev_info *bdi = wbc->bdi;
+
+ generic_sync_wb_inodes(&bdi->wb, sb, wbc);
+}
+
/*
* Write out a superblock's list of dirty inodes. A wait will be performed
* upon no inodes, all inodes or the final one, depending upon sync_mode.
diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index fb3b870..456154b 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -24,8 +24,8 @@ struct dentry;
* Bits in backing_dev_info.state
*/
enum bdi_state {
- BDI_pdflush, /* A pdflush thread is working this device */
BDI_pending, /* On its way to being activated */
+ BDI_wb_alloc, /* Default embedded wb allocated */
BDI_async_congested, /* The async (write) queue is getting full */
BDI_sync_congested, /* The sync queue is getting full */
BDI_unused, /* Available bits start here */
@@ -41,15 +41,22 @@ enum bdi_stat_item {

#define BDI_STAT_BATCH (8*(1+ilog2(nr_cpu_ids)))

-struct bdi_writeback_arg {
- unsigned long nr_pages;
- struct super_block *sb;
+struct bdi_writeback {
+ struct backing_dev_info *bdi; /* our parent bdi */
+ unsigned int nr;
+
+ struct task_struct *task; /* writeback task */
+ struct list_head b_dirty; /* dirty inodes */
+ struct list_head b_io; /* parked for writeback */
+ struct list_head b_more_io; /* parked for more writeback */
+
+ unsigned long nr_pages;
+ struct super_block *sb;
enum writeback_sync_modes sync_mode;
};

struct backing_dev_info {
struct list_head bdi_list;
-
unsigned long ra_pages; /* max readahead in PAGE_CACHE_SIZE units */
unsigned long state; /* Always use atomic bitops on this */
unsigned int capabilities; /* Device capabilities */
@@ -66,13 +73,11 @@ struct backing_dev_info {
unsigned int min_ratio;
unsigned int max_ratio, max_prop_frac;

- struct device *dev;
+ struct bdi_writeback wb; /* default writeback info for this bdi */
+ unsigned long wb_active; /* bitmap of active tasks */
+ unsigned long wb_mask; /* number of registered tasks */

- struct task_struct *task; /* writeback task */
- struct bdi_writeback_arg wb_arg; /* protected by BDI_pdflush */
- struct list_head b_dirty; /* dirty inodes */
- struct list_head b_io; /* parked for writeback */
- struct list_head b_more_io; /* parked for more writeback */
+ struct device *dev;

#ifdef CONFIG_DEBUG_FS
struct dentry *debug_dir;
@@ -89,17 +94,18 @@ int bdi_register_dev(struct backing_dev_info *bdi, dev_t dev);
void bdi_unregister(struct backing_dev_info *bdi);
void bdi_start_writeback(struct backing_dev_info *bdi, struct super_block *sb,
long nr_pages, enum writeback_sync_modes sync_mode);
-int bdi_writeback_task(struct backing_dev_info *bdi);
+int bdi_writeback_task(struct bdi_writeback *wb);
void bdi_writeback_all(struct super_block *sb, struct writeback_control *wbc);
+int bdi_has_dirty_io(struct backing_dev_info *bdi);

extern spinlock_t bdi_lock;
extern struct list_head bdi_list;

-static inline int bdi_has_dirty_io(struct backing_dev_info *bdi)
+static inline int wb_has_dirty_io(struct bdi_writeback *wb)
{
- return !list_empty(&bdi->b_dirty) ||
- !list_empty(&bdi->b_io) ||
- !list_empty(&bdi->b_more_io);
+ return !list_empty(&wb->b_dirty) ||
+ !list_empty(&wb->b_io) ||
+ !list_empty(&wb->b_more_io);
}

static inline void __add_bdi_stat(struct backing_dev_info *bdi,
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 9e17bae..5bd4984 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -215,10 +215,45 @@ static int __init default_bdi_init(void)
}
subsys_initcall(default_bdi_init);

+static void bdi_wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi)
+{
+ memset(wb, 0, sizeof(*wb));
+
+ wb->bdi = bdi;
+ INIT_LIST_HEAD(&wb->b_dirty);
+ INIT_LIST_HEAD(&wb->b_io);
+ INIT_LIST_HEAD(&wb->b_more_io);
+}
+
+static int wb_assign_nr(struct backing_dev_info *bdi, struct bdi_writeback *wb)
+{
+ set_bit(0, &bdi->wb_mask);
+ wb->nr = 0;
+ return 0;
+}
+
+static void bdi_put_wb(struct backing_dev_info *bdi, struct bdi_writeback *wb)
+{
+ clear_bit(wb->nr, &bdi->wb_mask);
+ clear_bit(BDI_wb_alloc, &bdi->state);
+}
+
+static struct bdi_writeback *bdi_new_wb(struct backing_dev_info *bdi)
+{
+ struct bdi_writeback *wb;
+
+ set_bit(BDI_wb_alloc, &bdi->state);
+ wb = &bdi->wb;
+ wb_assign_nr(bdi, wb);
+ return wb;
+}
+
static int bdi_start_fn(void *ptr)
{
- struct backing_dev_info *bdi = ptr;
+ struct bdi_writeback *wb = ptr;
+ struct backing_dev_info *bdi = wb->bdi;
struct task_struct *tsk = current;
+ int ret;

/*
* Add us to the active bdi_list
@@ -242,7 +277,16 @@ static int bdi_start_fn(void *ptr)
smp_mb__after_clear_bit();
wake_up_bit(&bdi->state, BDI_pending);

- return bdi_writeback_task(bdi);
+ ret = bdi_writeback_task(wb);
+
+ wb->task = NULL;
+ bdi_put_wb(bdi, wb);
+ return ret;
+}
+
+int bdi_has_dirty_io(struct backing_dev_info *bdi)
+{
+ return wb_has_dirty_io(&bdi->wb);
}

static void bdi_flush_io(struct backing_dev_info *bdi)
@@ -297,17 +341,18 @@ static void sync_supers_timer_fn(unsigned long unused)

static int bdi_forker_task(void *ptr)
{
- struct backing_dev_info *me = ptr;
+ struct bdi_writeback *me = ptr;

for (;;) {
struct backing_dev_info *bdi, *tmp;
+ struct bdi_writeback *wb;

/*
* Temporary measure, we want to make sure we don't see
* dirty data on the default backing_dev_info
*/
- if (bdi_has_dirty_io(me))
- bdi_flush_io(me);
+ if (wb_has_dirty_io(me))
+ bdi_flush_io(me->bdi);

spin_lock(&bdi_lock);

@@ -316,7 +361,7 @@ static int bdi_forker_task(void *ptr)
* a thread registered. If so, set that up.
*/
list_for_each_entry_safe(bdi, tmp, &bdi_list, bdi_list) {
- if (bdi->task || !bdi_has_dirty_io(bdi))
+ if (bdi->wb.task || !bdi_has_dirty_io(bdi))
continue;

bdi_add_default_flusher_task(bdi);
@@ -345,9 +390,11 @@ static int bdi_forker_task(void *ptr)
list_del_init(&bdi->bdi_list);
spin_unlock(&bdi_lock);

- BUG_ON(bdi->task);
+ wb = bdi_new_wb(bdi);
+ if (!wb)
+ goto readd_flush;

- bdi->task = kthread_run(bdi_start_fn, bdi, "flush-%s",
+ wb->task = kthread_run(bdi_start_fn, wb, "flush-%s",
dev_name(bdi->dev));
/*
* If task creation fails, then readd the bdi to
@@ -355,9 +402,10 @@ static int bdi_forker_task(void *ptr)
* from this forker thread. That will free some memory
* and we can try again.
*/
- if (IS_ERR(bdi->task)) {
- bdi->task = NULL;
-
+ if (IS_ERR(wb->task)) {
+ wb->task = NULL;
+ bdi_put_wb(bdi, wb);
+readd_flush:
/*
* Add this 'bdi' to the back, so we get
* a chance to flush other bdi's to free
@@ -380,6 +428,9 @@ static int bdi_forker_task(void *ptr)
*/
static void bdi_add_default_flusher_task(struct backing_dev_info *bdi)
{
+ if (!bdi_cap_writeback_dirty(bdi))
+ return;
+
/*
* Someone already marked this pending for task creation
*/
@@ -390,7 +441,7 @@ static void bdi_add_default_flusher_task(struct backing_dev_info *bdi)
list_move_tail(&bdi->bdi_list, &bdi_pending_list);
spin_unlock(&bdi_lock);

- wake_up_process(default_backing_dev_info.task);
+ wake_up_process(default_backing_dev_info.wb.task);
}

int bdi_register(struct backing_dev_info *bdi, struct device *parent,
@@ -423,14 +474,24 @@ int bdi_register(struct backing_dev_info *bdi, struct device *parent,
* on-demand when they need it.
*/
if (bdi_cap_flush_forker(bdi)) {
- bdi->task = kthread_run(bdi_forker_task, bdi, "bdi-%s",
+ struct bdi_writeback *wb;
+
+ wb = bdi_new_wb(bdi);
+ if (!wb) {
+ ret = -ENOMEM;
+ goto remove_err;
+ }
+
+ wb->task = kthread_run(bdi_forker_task, wb, "bdi-%s",
dev_name(dev));
- if (IS_ERR(bdi->task)) {
- bdi->task = NULL;
+ if (IS_ERR(wb->task)) {
+ wb->task = NULL;
+ bdi_put_wb(bdi, wb);
+ ret = -ENOMEM;
+remove_err:
spin_lock(&bdi_lock);
list_del(&bdi->bdi_list);
spin_unlock(&bdi_lock);
- ret = -ENOMEM;
goto exit;
}
}
@@ -454,10 +515,13 @@ static int sched_wait(void *word)
}

/*
- * Remove bdi from the global list
+ * Remove bdi from the global list and shutdown any threads we have running
*/
static void bdi_wb_shutdown(struct backing_dev_info *bdi)
{
+ if (!bdi_cap_writeback_dirty(bdi))
+ return;
+
/*
* If setup is pending, wait for that to complete first
*/
@@ -469,18 +533,18 @@ static void bdi_wb_shutdown(struct backing_dev_info *bdi)
spin_lock(&bdi_lock);
list_del(&bdi->bdi_list);
spin_unlock(&bdi_lock);
+
+ /*
+ * Finally, kill the kernel thread
+ */
+ kthread_stop(bdi->wb.task);
}

void bdi_unregister(struct backing_dev_info *bdi)
{
if (bdi->dev) {
- if (!bdi_cap_flush_forker(bdi)) {
+ if (!bdi_cap_flush_forker(bdi))
bdi_wb_shutdown(bdi);
- if (bdi->task) {
- kthread_stop(bdi->task);
- bdi->task = NULL;
- }
- }
bdi_debug_unregister(bdi);
device_unregister(bdi->dev);
bdi->dev = NULL;
@@ -498,9 +562,9 @@ int bdi_init(struct backing_dev_info *bdi)
bdi->max_ratio = 100;
bdi->max_prop_frac = PROP_FRAC_BASE;
INIT_LIST_HEAD(&bdi->bdi_list);
- INIT_LIST_HEAD(&bdi->b_io);
- INIT_LIST_HEAD(&bdi->b_dirty);
- INIT_LIST_HEAD(&bdi->b_more_io);
+ bdi->wb_mask = bdi->wb_active = 0;
+
+ bdi_wb_init(&bdi->wb, bdi);

for (i = 0; i < NR_BDI_STAT_ITEMS; i++) {
err = percpu_counter_init(&bdi->bdi_stat[i], 0);
@@ -525,9 +589,7 @@ void bdi_destroy(struct backing_dev_info *bdi)
{
int i;

- WARN_ON(!list_empty(&bdi->b_dirty));
- WARN_ON(!list_empty(&bdi->b_io));
- WARN_ON(!list_empty(&bdi->b_more_io));
+ WARN_ON(bdi_has_dirty_io(bdi));

bdi_unregister(bdi);

--
1.6.3.rc0.1.gf800

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