Commit 83ba7b071f30f7c01f72518ad72d5cd203c27502 broke writeback_in_progress()
as in that commit we started to remove work items from the list at the
moment we start working on them and not at the moment they are finished.
Thus if the flusher thread was doing some work but there was no other
work queued, writeback_in_progress() returned false. This could in
particular cause unnecessary queueing of background writeback from
balance_dirty_pages() or writeout work from writeback_sb_if_idle().
This patch fixes the problem by introducing a bit in the bdi state which
indicates that the flusher thread is processing some work and uses this
bit for writeback_in_progress() test.
NOTE: Both callsites of writeback_in_progress() (namely,
writeback_inodes_sb_if_idle() and balance_dirty_pages()) would actually
need a different information than what writeback_in_progress() provides.
They would need to know whether *the kind of writeback they are going
to submit* is already queued. But this information isn't that simple
to provide so let's fix writeback_in_progress() for the time being.
CC: hch@xxxxxxxxxxxxx
Signed-off-by: Jan Kara <jack@xxxxxxx>
---
fs/fs-writeback.c | 4 +++-
include/linux/backing-dev.h | 1 +
2 files changed, 4 insertions(+), 1 deletions(-)
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 542471e..6bdc924 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -59,7 +59,7 @@ struct wb_writeback_work {
*/
int writeback_in_progress(struct backing_dev_info *bdi)
{
- return !list_empty(&bdi->work_list);
+ return test_bit(BDI_writeback_running, &bdi->state);
}
static void bdi_queue_work(struct backing_dev_info *bdi,
@@ -751,6 +751,7 @@ long wb_do_writeback(struct bdi_writeback *wb, int force_wait)
struct wb_writeback_work *work;
long wrote = 0;
+ set_bit(BDI_writeback_running, &wb->bdi->state);
while ((work = get_next_work_item(bdi, wb)) != NULL) {
/*
* Override sync mode, in case we must wait for completion
@@ -775,6 +776,7 @@ long wb_do_writeback(struct bdi_writeback *wb, int force_wait)
* Check for periodic writeback, kupdated() style
*/
wrote += wb_check_old_data_flush(wb);
+ clear_bit(BDI_writeback_running, &wb->bdi->state);
return wrote;
}
diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index e9aec0d..12ba2cd 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -31,6 +31,7 @@ enum bdi_state {
BDI_async_congested, /* The async (write) queue is getting full */
BDI_sync_congested, /* The sync queue is getting full */
BDI_registered, /* bdi_register() was done */
+ BDI_writeback_running, /* Writeback is in progress */
BDI_unused, /* Available bits start here */
};
--
1.6.4.2
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