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Subject[PATCH 03/10] writeback: stop background writeback when below background threshold
Date
From: Wu Fengguang <fengguang.wu@intel.com>

Treat bdi_start_writeback(0) as a special request to do background write,
and stop such work when we are below the background dirty threshold.

Also simplify the (nr_pages <= 0) checks. Since we already pass in
nr_pages=LONG_MAX for WB_SYNC_ALL and background writes, we don't
need to worry about it being decreased to zero.

Reported-by: Richard Kennedy <richard@rsk.demon.co.uk>
CC: Jan Kara <jack@suse.cz>
CC: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
---
fs/fs-writeback.c | 28 +++++++++++++++++-----------
mm/page-writeback.c | 6 +++---
2 files changed, 20 insertions(+), 14 deletions(-)

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index c59d673..476be9b 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -41,8 +41,9 @@ struct wb_writeback_args {
long nr_pages;
struct super_block *sb;
enum writeback_sync_modes sync_mode;
- int for_kupdate;
- int range_cyclic;
+ int for_kupdate:1;
+ int range_cyclic:1;
+ int for_background:1;
};

/*
@@ -257,6 +258,15 @@ void bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages)
.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);
}

@@ -720,20 +730,16 @@ static long wb_writeback(struct bdi_writeback *wb,

for (;;) {
/*
- * Don't flush anything for non-integrity writeback where
- * no nr_pages was given
+ * Stop writeback when nr_pages has been consumed
*/
- if (!args->for_kupdate && args->nr_pages <= 0 &&
- args->sync_mode == WB_SYNC_NONE)
+ if (args->nr_pages <= 0)
break;

/*
- * If no specific pages were given and this is just a
- * periodic background writeout and we are below the
- * background dirty threshold, don't do anything
+ * For background writeout, stop when we are below the
+ * background dirty threshold
*/
- if (args->for_kupdate && args->nr_pages <= 0 &&
- !over_bground_thresh())
+ if (args->for_background && !over_bground_thresh())
break;

wbc.more_io = 0;
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index cbd4cba..3c78fc3 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -593,10 +593,10 @@ static void balance_dirty_pages(struct address_space *mapping,
* background_thresh, to keep the amount of dirty memory low.
*/
if ((laptop_mode && pages_written) ||
- (!laptop_mode && ((nr_writeback = global_page_state(NR_FILE_DIRTY)
- + global_page_state(NR_UNSTABLE_NFS))
+ (!laptop_mode && ((global_page_state(NR_FILE_DIRTY)
+ + global_page_state(NR_UNSTABLE_NFS))
> background_thresh)))
- bdi_start_writeback(bdi, nr_writeback);
+ bdi_start_writeback(bdi, 0);
}

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


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