From 81d73a32d775ae9674ea6edf0b5b721fc3bc57d9 Mon Sep 17 00:00:00 2001 From: Jan Kara Date: Wed, 11 Aug 2010 14:17:44 -0700 Subject: [PATCH] mm: fix writeback_in_progress() Commit 83ba7b071f3 ("writeback: simplify the write back thread queue") 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. Signed-off-by: Jan Kara Cc: Christoph Hellwig Cc: Wu Fengguang Acked-by: Jens Axboe Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/fs-writeback.c | 4 +++- include/linux/backing-dev.h | 1 + 2 files changed, 4 insertions(+), 1 deletion(-) diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index 8a5807d2fb9..7d9d06ba184 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -68,7 +68,7 @@ int nr_pdflush_threads; */ 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, @@ -740,6 +740,7 @@ 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)) != NULL) { /* * Override sync mode, in case we must wait for completion @@ -766,6 +767,7 @@ 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 7628219e538..35b00746c71 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 */ }; -- 2.20.1