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writeback: Fix occasional slow sync(1)

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In case when system contains no dirty pages, wakeup_flusher_threads()
will submit WB_SYNC_NONE writeback for 0 pages so wb_writeback() exits
immediately without doing anything. Thus sync(1) will write all the
dirty inodes from a WB_SYNC_ALL writeback pass which is slow.

Fix the problem by using get_nr_dirty_pages() in
wakeup_flusher_threads() instead of calculating number of dirty pages
manually. That function also takes number of dirty inodes into account.

Change-Id: I458027ae08d9a5a93202a7b97ace1f8da7a18a07
CC: stable@vger.kernel.org
Reported-by: Paul Taysom <taysom@chromium.org>
Signed-off-by: Jan Kara <jack@suse.cz>
This commit is contained in:
Jan Kara 2013-07-12 17:30:07 +02:00 committed by Zhao Wei Liew
parent 73af84d854
commit 3b1a823ca1
1 changed files with 2 additions and 4 deletions
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6
fs/fs-writeback.c
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@ -999,10 +999,8 @@ void wakeup_flusher_threads(long nr_pages, enum wb_reason reason)
{
struct backing_dev_info *bdi;
if (!nr_pages) {
nr_pages = global_page_state(NR_FILE_DIRTY) +
global_page_state(NR_UNSTABLE_NFS);
}
if (!nr_pages)
nr_pages = get_nr_dirty_pages();
rcu_read_lock();
list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) {