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Subject[PATCH 09/11] writeback: separate starting of sync vs opportunistic writeback
Date
bdi_start_writeback() is currently split into two paths, one for
WB_SYNC_NONE and one for WB_SYNC_ALL. Add bdi_sync_writeback()
for WB_SYNC_ALL writeback and let bdi_start_writeback() handle
only WB_SYNC_NONE.

Push down the writeback_control allocation and only accept the
parameters that make sense for each function. This cleans up
the API considerably.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
---
fs/fs-writeback.c | 133 ++++++++++++++++++++++---------------------
fs/ubifs/budget.c | 20 +------
include/linux/backing-dev.h | 2 +-
include/linux/writeback.h | 4 +-
mm/page-writeback.c | 12 +---
5 files changed, 77 insertions(+), 94 deletions(-)
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index af2e79a..3de93a9 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -74,13 +74,10 @@ static inline bool bdi_work_on_stack(struct bdi_work *work)
}

static inline void bdi_work_init(struct bdi_work *work,
- struct writeback_control *wbc)
+ struct wb_writeback_args *args)
{
INIT_RCU_HEAD(&work->rcu_head);
- work->args.sb = wbc->sb;
- work->args.nr_pages = wbc->nr_to_write;
- work->args.sync_mode = wbc->sync_mode;
- work->args.range_cyclic = wbc->range_cyclic;
+ work->args = *args;
work->state = WS_USED;
}

@@ -193,7 +190,7 @@ static void bdi_wait_on_work_clear(struct bdi_work *work)
}

static void bdi_alloc_queue_work(struct backing_dev_info *bdi,
- struct writeback_control *wbc)
+ struct wb_writeback_args *args)
{
struct bdi_work *work;

@@ -203,7 +200,7 @@ static void bdi_alloc_queue_work(struct backing_dev_info *bdi,
*/
work = kmalloc(sizeof(*work), GFP_ATOMIC);
if (work) {
- bdi_work_init(work, wbc);
+ bdi_work_init(work, args);
bdi_queue_work(bdi, work);
} else {
struct bdi_writeback *wb = &bdi->wb;
@@ -213,24 +210,54 @@ static void bdi_alloc_queue_work(struct backing_dev_info *bdi,
}
}

-void bdi_start_writeback(struct writeback_control *wbc)
+/**
+ * bdi_sync_writeback - start and wait for writeback
+ * @bdi: the backing device to write from
+ * @sb: write inodes from this super_block
+ *
+ * Description:
+ * This does WB_SYNC_ALL data integrity writeback and waits for the
+ * IO to complete. Callers must hold the sb s_umount semaphore for
+ * reading, to avoid having the super disappear before we are done.
+ */
+static void bdi_sync_writeback(struct backing_dev_info *bdi,
+ struct super_block *sb)
{
- /*
- * WB_SYNC_NONE is opportunistic writeback. If this allocation fails,
- * bdi_queue_work() will wake up the thread and flush old data. This
- * should ensure some amount of progress in freeing memory.
- */
- if (wbc->sync_mode != WB_SYNC_ALL)
- bdi_alloc_queue_work(wbc->bdi, wbc);
- else {
- struct bdi_work work;
+ struct wb_writeback_args args = {
+ .sb = sb,
+ .sync_mode = WB_SYNC_ALL,
+ .nr_pages = LONG_MAX,
+ .range_cyclic = 0,
+ };
+ struct bdi_work work;

- bdi_work_init(&work, wbc);
- work.state |= WS_ONSTACK;
+ bdi_work_init(&work, &args);
+ work.state |= WS_ONSTACK;

- bdi_queue_work(wbc->bdi, &work);
- bdi_wait_on_work_clear(&work);
- }
+ bdi_queue_work(bdi, &work);
+ bdi_wait_on_work_clear(&work);
+}
+
+/**
+ * bdi_start_writeback - start writeback
+ * @bdi: the backing device to write from
+ * @nr_pages: the number of pages to write
+ *
+ * Description:
+ * This does WB_SYNC_NONE opportunistic writeback. The IO is only
+ * started when this function returns, we make no guarentees on
+ * completion. Caller need not hold sb s_umount semaphore.
+ *
+ */
+void bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages)
+{
+ struct wb_writeback_args args = {
+ .sync_mode = WB_SYNC_NONE,
+ .nr_pages = nr_pages,
+ .range_cyclic = 1,
+ };
+
+ bdi_alloc_queue_work(bdi, &args);
}

/*
@@ -771,6 +798,8 @@ static long wb_check_old_data_flush(struct bdi_writeback *wb)
struct wb_writeback_args args = {
.nr_pages = nr_pages,
.sync_mode = WB_SYNC_NONE,
+ .for_kupdate = 1,
+ .range_cyclic = 1,
};

return wb_writeback(wb, &args);
@@ -860,23 +889,25 @@ int bdi_writeback_task(struct bdi_writeback *wb)
}

/*
- * Schedule writeback for all backing devices. Can only be used for
- * WB_SYNC_NONE writeback, WB_SYNC_ALL should use bdi_start_writeback()
- * and pass in the superblock.
+ * Schedule writeback for all backing devices. This does WB_SYNC_NONE
+ * writeback, for integrity writeback see bdi_sync_writeback().
*/
-static void bdi_writeback_all(struct writeback_control *wbc)
+static void bdi_writeback_all(struct super_block *sb, long nr_pages)
{
+ struct wb_writeback_args args = {
+ .sb = sb,
+ .nr_pages = nr_pages,
+ .sync_mode = WB_SYNC_NONE,
+ };
struct backing_dev_info *bdi;

- WARN_ON(wbc->sync_mode == WB_SYNC_ALL);
-
rcu_read_lock();

list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) {
if (!bdi_has_dirty_io(bdi))
continue;

- bdi_alloc_queue_work(bdi, wbc);
+ bdi_alloc_queue_work(bdi, &args);
}

rcu_read_unlock();
@@ -888,17 +919,10 @@ static void bdi_writeback_all(struct writeback_control *wbc)
*/
void wakeup_flusher_threads(long nr_pages)
{
- struct writeback_control wbc = {
- .sync_mode = WB_SYNC_NONE,
- .older_than_this = NULL,
- .range_cyclic = 1,
- };
-
if (nr_pages == 0)
nr_pages = global_page_state(NR_FILE_DIRTY) +
global_page_state(NR_UNSTABLE_NFS);
- wbc.nr_to_write = nr_pages;
- bdi_writeback_all(&wbc);
+ bdi_writeback_all(NULL, nr_pages);
}

static noinline void block_dump___mark_inode_dirty(struct inode *inode)
@@ -1045,7 +1069,7 @@ EXPORT_SYMBOL(__mark_inode_dirty);
* on the writer throttling path, and we get decent balancing between many
* throttled threads: we don't want them all piling up on inode_sync_wait.
*/
-static void wait_sb_inodes(struct writeback_control *wbc)
+static void wait_sb_inodes(struct super_block *sb)
{
struct inode *inode, *old_inode = NULL;

@@ -1053,7 +1077,7 @@ static void wait_sb_inodes(struct writeback_control *wbc)
* We need to be protected against the filesystem going from
* r/o to r/w or vice versa.
*/
- WARN_ON(!rwsem_is_locked(&wbc->sb->s_umount));
+ WARN_ON(!rwsem_is_locked(&sb->s_umount));

spin_lock(&inode_lock);

@@ -1064,7 +1088,7 @@ static void wait_sb_inodes(struct writeback_control *wbc)
* In which case, the inode may not be on the dirty list, but
* we still have to wait for that writeout.
*/
- list_for_each_entry(inode, &wbc->sb->s_inodes, i_sb_list) {
+ list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
struct address_space *mapping;

if (inode->i_state & (I_FREEING|I_CLEAR|I_WILL_FREE|I_NEW))
@@ -1104,14 +1128,8 @@ static void wait_sb_inodes(struct writeback_control *wbc)
* for IO completion of submitted IO. The number of pages submitted is
* returned.
*/
-long writeback_inodes_sb(struct super_block *sb)
+void writeback_inodes_sb(struct super_block *sb)
{
- struct writeback_control wbc = {
- .sb = sb,
- .sync_mode = WB_SYNC_NONE,
- .range_start = 0,
- .range_end = LLONG_MAX,
- };
unsigned long nr_dirty = global_page_state(NR_FILE_DIRTY);
unsigned long nr_unstable = global_page_state(NR_UNSTABLE_NFS);
long nr_to_write;
@@ -1119,9 +1137,7 @@ long writeback_inodes_sb(struct super_block *sb)
nr_to_write = nr_dirty + nr_unstable +
(inodes_stat.nr_inodes - inodes_stat.nr_unused);

- wbc.nr_to_write = nr_to_write;
- bdi_writeback_all(&wbc);
- return nr_to_write - wbc.nr_to_write;
+ bdi_writeback_all(sb, nr_to_write);
}
EXPORT_SYMBOL(writeback_inodes_sb);

@@ -1132,21 +1148,10 @@ EXPORT_SYMBOL(writeback_inodes_sb);
* This function writes and waits on any dirty inode belonging to this
* super_block. The number of pages synced is returned.
*/
-long sync_inodes_sb(struct super_block *sb)
+void sync_inodes_sb(struct super_block *sb)
{
- struct writeback_control wbc = {
- .sb = sb,
- .bdi = sb->s_bdi,
- .sync_mode = WB_SYNC_ALL,
- .range_start = 0,
- .range_end = LLONG_MAX,
- };
- long nr_to_write = LONG_MAX; /* doesn't actually matter */
-
- wbc.nr_to_write = nr_to_write;
- bdi_start_writeback(&wbc);
- wait_sb_inodes(&wbc);
- return nr_to_write - wbc.nr_to_write;
+ bdi_sync_writeback(sb->s_bdi, sb);
+ wait_sb_inodes(sb);
}
EXPORT_SYMBOL(sync_inodes_sb);

diff --git a/fs/ubifs/budget.c b/fs/ubifs/budget.c
index 1c8991b..ee1ce68 100644
--- a/fs/ubifs/budget.c
+++ b/fs/ubifs/budget.c
@@ -54,29 +54,15 @@
* @nr_to_write: how many dirty pages to write-back
*
* This function shrinks UBIFS liability by means of writing back some amount
- * of dirty inodes and their pages. Returns the amount of pages which were
- * written back. The returned value does not include dirty inodes which were
- * synchronized.
+ * of dirty inodes and their pages.
*
* Note, this function synchronizes even VFS inodes which are locked
* (@i_mutex) by the caller of the budgeting function, because write-back does
* not touch @i_mutex.
*/
-static int shrink_liability(struct ubifs_info *c, int nr_to_write)
+static void shrink_liability(struct ubifs_info *c, int nr_to_write)
{
- int nr_written;
-
- nr_written = writeback_inodes_sb(c->vfs_sb);
- if (!nr_written) {
- /*
- * Re-try again but wait on pages/inodes which are being
- * written-back concurrently (e.g., by pdflush).
- */
- nr_written = sync_inodes_sb(c->vfs_sb);
- }
-
- dbg_budg("%d pages were written back", nr_written);
- return nr_written;
+ writeback_inodes_sb(c->vfs_sb);
}

/**
diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index 859e797..0ee33c2 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -101,7 +101,7 @@ int bdi_register(struct backing_dev_info *bdi, struct device *parent,
const char *fmt, ...);
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 writeback_control *wbc);
+void bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages);
int bdi_writeback_task(struct bdi_writeback *wb);
int bdi_has_dirty_io(struct backing_dev_info *bdi);

diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index 48a054e..75cf586 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -68,8 +68,8 @@ struct writeback_control {
*/
struct bdi_writeback;
int inode_wait(void *);
-long writeback_inodes_sb(struct super_block *);
-long sync_inodes_sb(struct super_block *);
+void writeback_inodes_sb(struct super_block *);
+void sync_inodes_sb(struct super_block *);
void writeback_inodes_wbc(struct writeback_control *wbc);
long wb_do_writeback(struct bdi_writeback *wb, int force_wait);
void wakeup_flusher_threads(long nr_pages);
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index da6ee07..f579189 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -582,16 +582,8 @@ static void balance_dirty_pages(struct address_space *mapping)
if ((laptop_mode && pages_written) ||
(!laptop_mode && ((nr_writeback = global_page_state(NR_FILE_DIRTY)
+ global_page_state(NR_UNSTABLE_NFS))
- > background_thresh))) {
- struct writeback_control wbc = {
- .bdi = bdi,
- .sync_mode = WB_SYNC_NONE,
- .nr_to_write = nr_writeback,
- };
-
-
- bdi_start_writeback(&wbc);
- }
+ > background_thresh)))
+ bdi_start_writeback(bdi, nr_writeback);
}

void set_page_dirty_balance(struct page *page, int page_mkwrite)
--
1.6.4.1.207.g68ea


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