[PATCH 6/7] writeback: separate starting of sync vs opportunistic writeback

Jens Axboe
2009-09-14T09:36:50Z

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.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
---
fs/fs-writeback.c | 51 ++++++++++++++++++++++++++++++++++-----------------
mm/page-writeback.c | 1 -
2 files changed, 34 insertions(+), 18 deletions(-)

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 5cd8b3b..64ca471 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -204,24 +204,42 @@ 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
+ * @wbc: writeback parameters
+ *
+ * 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 writeback_control *wbc)
{
- /*
- * 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 bdi_work work;

- bdi_work_init(&work, wbc);
- work.state |= WS_ONSTACK;
+ wbc->sync_mode = WB_SYNC_ALL;

- bdi_queue_work(wbc->bdi, &work);
- bdi_wait_on_work_clear(&work);
- }
+ bdi_work_init(&work, wbc);
+ work.state |= WS_ONSTACK;
+
+ bdi_queue_work(wbc->bdi, &work);
+ bdi_wait_on_work_clear(&work);
+}
+
+/**
+ * bdi_start_writeback - start writeback
+ * @wbc: writeback parameters
+ *
+ * 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 writeback_control *wbc)
+{
+ wbc->sync_mode = WB_SYNC_NONE;
+ bdi_alloc_queue_work(wbc->bdi, wbc);
}

/*
@@ -1119,14 +1137,13 @@ long 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);
+ bdi_sync_writeback(&wbc);
wait_sb_inodes(&wbc);
return nr_to_write - wbc.nr_to_write;
}
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index a5f0f76..f61f0cc 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -585,7 +585,6 @@ static void balance_dirty_pages(struct address_space *mapping)
> background_thresh))) {
struct writeback_control wbc = {
.bdi = bdi,
- .sync_mode = WB_SYNC_NONE,
.nr_to_write = nr_writeback,
};

--
1.6.4.1.207.g68ea