[PATCH 1/5] writeback: introduce wbc.for_sync to cover the two sync stages

Wu Fengguang
2010-07-29T11:51:43Z

[-- Attachment #1: writeback-for-sync.patch --]
[-- Type: text/plain, Size: 2990 bytes --]

The sync() is performed in two stages: the WB_SYNC_NONE sync and
the WB_SYNC_ALL sync. It is necessary to tag both stages with
wbc.for_sync, so as to prevent either of them being livelocked.

The basic livelock scheme will be based on the sync_after timestamp.
Inodes dirtied after that won't be queued for IO. The timestamp could be
recorded as early as the sync() time, this patch lazily sets it in
writeback_inodes_sb()/sync_inodes_sb(). This will stop livelock, but
may do more work than necessary.

Note that writeback_inodes_sb() is called by not only sync(), they
are treated the same because the other callers need the same livelock
prevention.

CC: Jan Kara <jack@suse.cz>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
---
fs/fs-writeback.c | 21 ++++++++++++---------
include/linux/writeback.h | 1 +
2 files changed, 13 insertions(+), 9 deletions(-)

--- linux-next.orig/fs/fs-writeback.c 2010-07-28 17:05:17.000000000 +0800
+++ linux-next/fs/fs-writeback.c 2010-07-28 21:21:31.000000000 +0800
@@ -36,6 +36,8 @@ struct wb_writeback_work {
long nr_pages;
struct super_block *sb;
enum writeback_sync_modes sync_mode;
+ unsigned long sync_after;
+ unsigned int for_sync:1;
unsigned int for_kupdate:1;
unsigned int range_cyclic:1;
unsigned int for_background:1;
@@ -1086,20 +1090,17 @@ static void wait_sb_inodes(struct super_
*/
void writeback_inodes_sb(struct super_block *sb)
{
- unsigned long nr_dirty = global_page_state(NR_FILE_DIRTY);
- unsigned long nr_unstable = global_page_state(NR_UNSTABLE_NFS);
DECLARE_COMPLETION_ONSTACK(done);
struct wb_writeback_work work = {
.sb = sb,
.sync_mode = WB_SYNC_NONE,
+ .for_sync = 1,
+ .sync_after = jiffies,
.done = &done,
};

WARN_ON(!rwsem_is_locked(&sb->s_umount));

- work.nr_pages = nr_dirty + nr_unstable +
- (inodes_stat.nr_inodes - inodes_stat.nr_unused);
-
bdi_queue_work(sb->s_bdi, &work);
wait_for_completion(&done);
}
@@ -1137,6 +1138,8 @@ void sync_inodes_sb(struct super_block *
struct wb_writeback_work work = {
.sb = sb,
.sync_mode = WB_SYNC_ALL,
+ .for_sync = 1,
+ .sync_after = jiffies,
.nr_pages = LONG_MAX,
.range_cyclic = 0,
.done = &done,
--- linux-next.orig/include/linux/writeback.h 2010-07-28 17:05:17.000000000 +0800
+++ linux-next/include/linux/writeback.h 2010-07-28 21:24:54.000000000 +0800
@@ -48,6 +48,7 @@ struct writeback_control {
unsigned encountered_congestion:1; /* An output: a queue is full */
unsigned for_kupdate:1; /* A kupdate writeback */
unsigned for_background:1; /* A background writeback */
+ unsigned for_sync:1; /* A writeback for sync */
unsigned for_reclaim:1; /* Invoked from the page allocator */
unsigned range_cyclic:1; /* range_start is cyclic */
};