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From: Wu Fengguang on 7 Oct 2009 04:10
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 next patch will utilize this flag to do the livelock prevention.

CC: Jan Kara <jack(a)suse.cz>
Signed-off-by: Wu Fengguang <fengguang.wu(a)intel.com>
---
fs/fs-writeback.c | 30 +++++++++---------------------
include/linux/backing-dev.h | 2 +-
include/linux/writeback.h | 11 +++++++++++
mm/page-writeback.c | 2 +-
4 files changed, 22 insertions(+), 23 deletions(-)

--- linux.orig/fs/fs-writeback.c 2009-10-06 23:39:32.000000000 +0800
+++ linux/fs/fs-writeback.c 2009-10-06 23:39:33.000000000 +0800
@@ -42,6 +42,7 @@ struct wb_writeback_args {
long nr_pages;
struct super_block *sb;
enum writeback_sync_modes sync_mode;
+ int for_sync:1;
int for_kupdate:1;
int range_cyclic:1;
int for_background:1;
@@ -221,6 +222,7 @@ static void bdi_sync_writeback(struct ba
struct wb_writeback_args args = {
.sb = sb,
.sync_mode = WB_SYNC_ALL,
+ .for_sync = 1,
.nr_pages = LONG_MAX,
.range_cyclic = 0,
};
@@ -236,7 +238,6 @@ static void bdi_sync_writeback(struct ba
/**
* 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
@@ -245,24 +246,17 @@ static void bdi_sync_writeback(struct ba
*
*/
void bdi_start_writeback(struct backing_dev_info *bdi, struct super_block *sb,
- long nr_pages)
+ long mission)
{
struct wb_writeback_args args = {
.sb = sb,
.sync_mode = WB_SYNC_NONE,
- .nr_pages = nr_pages,
+ .nr_pages = LONG_MAX,
+ .for_background = mission == WB_FOR_BACKGROUND,
+ .for_sync = mission == WB_FOR_SYNC,
.range_cyclic = 1,
};

- /*
- * We treat @nr_pages=0 as the special case to do background writeback,
- * ie. to sync pages until the background dirty threshold is reached.
- */
- if (!nr_pages) {
- args.nr_pages = LONG_MAX;
- args.for_background = 1;
- }
-
bdi_alloc_queue_work(bdi, &args);
}

@@ -310,7 +304,7 @@ void bdi_writeback_wait(struct backing_d
* make sure we will be woke up by someone
*/
if (can_submit_background_writeback(bdi))
- bdi_start_writeback(bdi, NULL, 0);
+ bdi_start_writeback(bdi, NULL, WB_FOR_BACKGROUND);

wait_for_completion(&tt.complete);
}
@@ -790,6 +784,7 @@ static long wb_writeback(struct bdi_writ
.older_than_this = NULL,
.for_kupdate = args->for_kupdate,
.for_background = args->for_background,
+ .for_sync = args->for_sync,
.range_cyclic = args->range_cyclic,
};
unsigned long oldest_jif;
@@ -1250,14 +1245,7 @@ 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);
- long nr_to_write;
-
- nr_to_write = nr_dirty + nr_unstable +
- (inodes_stat.nr_inodes - inodes_stat.nr_unused);
-
- bdi_start_writeback(sb->s_bdi, sb, nr_to_write);
+ bdi_start_writeback(sb->s_bdi, sb, WB_FOR_SYNC);
}
EXPORT_SYMBOL(writeback_inodes_sb);

--- linux.orig/include/linux/backing-dev.h 2009-10-06 23:39:26.000000000 +0800
+++ linux/include/linux/backing-dev.h 2009-10-06 23:39:33.000000000 +0800
@@ -123,7 +123,7 @@ int bdi_register(struct backing_dev_info
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);
+ long mission);
int bdi_writeback_task(struct bdi_writeback *wb);
int bdi_has_dirty_io(struct backing_dev_info *bdi);
int bdi_writeback_wakeup(struct backing_dev_info *bdi);
--- linux.orig/include/linux/writeback.h 2009-10-06 23:39:28.000000000 +0800
+++ linux/include/linux/writeback.h 2009-10-06 23:39:33.000000000 +0800
@@ -31,6 +31,16 @@ enum writeback_sync_modes {
WB_SYNC_ALL, /* Wait on every mapping */
};

+enum writeback_mission {
+ WB_FOR_KUPDATE, /* writeback expired dirty inodes */
+ WB_FOR_RECLAIM,
+ WB_FOR_BACKGROUND, /* stop on hitting background threshold */
+ WB_FOR_SYNC, /* write all now-dirty inodes/pages,
+ * but take care not to live lock
+ */
+ WB_NR_PAGES, /* writeback # of pages if larger than this */
+};
+
/*
* A control structure which tells the writeback code what to do. These are
* always on the stack, and hence need no locking. They are always initialised
@@ -65,6 +75,7 @@ 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 */
unsigned more_io:1; /* more io to be dispatched */
--- linux.orig/mm/page-writeback.c 2009-10-06 23:39:30.000000000 +0800
+++ linux/mm/page-writeback.c 2009-10-06 23:39:33.000000000 +0800
@@ -529,7 +529,7 @@ out:
*/
if (!laptop_mode && (nr_reclaimable > background_thresh) &&
can_submit_background_writeback(bdi))
- bdi_start_writeback(bdi, NULL, 0);
+ bdi_start_writeback(bdi, NULL, WB_FOR_BACKGROUND);
}

void set_page_dirty_balance(struct page *page, int page_mkwrite)


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Prev: [PATCH 6/6] haptic: ISA1200 haptic device support
Next: [PATCH 03/45] ext4: remove unused parameter wbc from __ext4_journalled_writepage()