writeback: separate starting of sync vs opportunistic writeback

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>

1 files changed, 67 insertions, 65 deletions

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 59b3ee63b624..5887328b5a06 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -74,14 +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.for_kupdate = 0;
+        work->args = *args;
         work->state = WS_USED;
 }
 
@@ -194,7 +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;
 
@@ -204,7 +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;
@@ -214,24 +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);
 }
 
 /*
@@ -863,23 +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();
@@ -891,17 +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)
@@ -1048,7 +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;
 
@@ -1056,7 +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);
 
@@ -1067,7 +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))
@@ -1107,14 +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;
@@ -1122,9 +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);
 
@@ -1135,21 +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);