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Date: Mon, 25 May 2009 16:02:38 +0800
From: "Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
To: Jens Axboe <jens.axboe@...cle.com>
Cc: Jan Kara <jack@...e.cz>, linux-kernel@...r.kernel.org,
linux-fsdevel@...r.kernel.org, chris.mason@...cle.com,
david@...morbit.com, hch@...radead.org, akpm@...ux-foundation.org
Subject: Re: [PATCH 0/11] Per-bdi writeback flusher threads #4
On Sat, 2009-05-23 at 21:15 +0200, Jens Axboe wrote:
> On Fri, May 22 2009, Jens Axboe wrote:
> > Please try with this combined patch against what you are running now, it
> > should resolve the issue. It needs a bit more work, but I'm running out
> > of time today. I'l get it finalized, cleaned up, and integrated. Then
> > I'll post a new revision of the patch set.
> >
>
> This one has been tested good and has a few more tweaks. So please try
> that! It should be pretty close to final now, will repost the series on
> monday.
I ran the workload for 10 times and didn't trigger it yet. So the bug is
fixed.
yanmin
>
> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> index f80afaa..33357c3 100644
> --- a/fs/fs-writeback.c
> +++ b/fs/fs-writeback.c
> @@ -50,6 +50,7 @@ struct bdi_work {
>
> unsigned long sb_data;
> unsigned long nr_pages;
> + enum writeback_sync_modes sync_mode;
>
> unsigned long state;
> };
> @@ -65,19 +66,22 @@ static inline bool bdi_work_on_stack(struct bdi_work *work)
> }
>
> static inline void bdi_work_init(struct bdi_work *work, struct super_block *sb,
> - unsigned long nr_pages)
> + unsigned long nr_pages,
> + enum writeback_sync_modes sync_mode)
> {
> INIT_RCU_HEAD(&work->rcu_head);
> work->sb_data = (unsigned long) sb;
> work->nr_pages = nr_pages;
> + work->sync_mode = sync_mode;
> work->state = 0;
> }
>
> static inline void bdi_work_init_on_stack(struct bdi_work *work,
> struct super_block *sb,
> - unsigned long nr_pages)
> + unsigned long nr_pages,
> + enum writeback_sync_modes sync_mode)
> {
> - bdi_work_init(work, sb, nr_pages);
> + bdi_work_init(work, sb, nr_pages, sync_mode);
> set_bit(0, &work->state);
> work->sb_data |= 1UL;
> }
> @@ -136,6 +140,9 @@ static void wb_start_writeback(struct bdi_writeback *wb, struct bdi_work *work)
> wake_up(&wb->wait);
> }
>
> +/*
> + * Add work to bdi work list.
> + */
> static int bdi_queue_writeback(struct backing_dev_info *bdi,
> struct bdi_work *work)
> {
> @@ -189,17 +196,17 @@ static void bdi_wait_on_work_start(struct bdi_work *work)
> }
>
> int bdi_start_writeback(struct backing_dev_info *bdi, struct super_block *sb,
> - long nr_pages)
> + long nr_pages, enum writeback_sync_modes sync_mode)
> {
> struct bdi_work work_stack, *work;
> int ret;
>
> work = kmalloc(sizeof(*work), GFP_ATOMIC);
> if (work)
> - bdi_work_init(work, sb, nr_pages);
> + bdi_work_init(work, sb, nr_pages, sync_mode);
> else {
> work = &work_stack;
> - bdi_work_init_on_stack(work, sb, nr_pages);
> + bdi_work_init_on_stack(work, sb, nr_pages, sync_mode);
> }
>
> ret = bdi_queue_writeback(bdi, work);
> @@ -273,24 +280,31 @@ static long wb_kupdated(struct bdi_writeback *wb)
> return wrote;
> }
>
> +static inline bool over_bground_thresh(void)
> +{
> + unsigned long background_thresh, dirty_thresh;
> +
> + get_dirty_limits(&background_thresh, &dirty_thresh, NULL, NULL);
> +
> + return (global_page_state(NR_FILE_DIRTY) +
> + global_page_state(NR_UNSTABLE_NFS) >= background_thresh);
> +}
> +
> static long __wb_writeback(struct bdi_writeback *wb, long nr_pages,
> - struct super_block *sb)
> + struct super_block *sb,
> + enum writeback_sync_modes sync_mode)
> {
> struct writeback_control wbc = {
> .bdi = wb->bdi,
> - .sync_mode = WB_SYNC_NONE,
> + .sync_mode = sync_mode,
> .older_than_this = NULL,
> .range_cyclic = 1,
> };
> long wrote = 0;
>
> for (;;) {
> - unsigned long background_thresh, dirty_thresh;
> -
> - get_dirty_limits(&background_thresh, &dirty_thresh, NULL, NULL);
> - if ((global_page_state(NR_FILE_DIRTY) +
> - global_page_state(NR_UNSTABLE_NFS) < background_thresh) &&
> - nr_pages <= 0)
> + if (sync_mode == WB_SYNC_NONE && nr_pages <= 0 &&
> + !over_bground_thresh())
> break;
>
> wbc.more_io = 0;
> @@ -345,9 +359,10 @@ static long wb_writeback(struct bdi_writeback *wb)
> while ((work = get_next_work_item(bdi, wb)) != NULL) {
> struct super_block *sb = bdi_work_sb(work);
> long nr_pages = work->nr_pages;
> + enum writeback_sync_modes sync_mode = work->sync_mode;
>
> wb_clear_pending(wb, work);
> - wrote += __wb_writeback(wb, nr_pages, sb);
> + wrote += __wb_writeback(wb, nr_pages, sb, sync_mode);
> }
>
> return wrote;
> @@ -420,39 +435,36 @@ int bdi_writeback_task(struct bdi_writeback *wb)
> return 0;
> }
>
> -void bdi_writeback_all(struct super_block *sb, long nr_pages)
> +/*
> + * Do in-line writeback for all backing devices. Expensive!
> + */
> +void bdi_writeback_all(struct super_block *sb, long nr_pages,
> + enum writeback_sync_modes sync_mode)
> {
> - struct list_head *entry = &bdi_list;
> + struct backing_dev_info *bdi, *tmp;
>
> - rcu_read_lock();
> -
> - list_for_each_continue_rcu(entry, &bdi_list) {
> - struct backing_dev_info *bdi;
> - struct list_head *next;
> - struct bdi_work *work;
> + mutex_lock(&bdi_lock);
>
> - bdi = list_entry(entry, struct backing_dev_info, bdi_list);
> + list_for_each_entry_safe(bdi, tmp, &bdi_list, bdi_list) {
> if (!bdi_has_dirty_io(bdi))
> continue;
>
> - /*
> - * If this allocation fails, we just wakeup the thread and
> - * let it do kupdate writeback
> - */
> - work = kmalloc(sizeof(*work), GFP_ATOMIC);
> - if (work)
> - bdi_work_init(work, sb, nr_pages);
> + if (!bdi_wblist_needs_lock(bdi))
> + __wb_writeback(&bdi->wb, 0, sb, sync_mode);
> + else {
> + struct bdi_writeback *wb;
> + int idx;
>
> - /*
> - * Prepare to start from previous entry if this one gets moved
> - * to the bdi_pending list.
> - */
> - next = entry->prev;
> - if (bdi_queue_writeback(bdi, work))
> - entry = next;
> + idx = srcu_read_lock(&bdi->srcu);
> +
> + list_for_each_entry_rcu(wb, &bdi->wb_list, list)
> + __wb_writeback(&bdi->wb, 0, sb, sync_mode);
> +
> + srcu_read_unlock(&bdi->srcu, idx);
> + }
> }
>
> - rcu_read_unlock();
> + mutex_unlock(&bdi_lock);
> }
>
> /*
> @@ -972,9 +984,9 @@ void generic_sync_sb_inodes(struct super_block *sb,
> struct writeback_control *wbc)
> {
> if (wbc->bdi)
> - bdi_start_writeback(wbc->bdi, sb, 0);
> + generic_sync_bdi_inodes(sb, wbc);
> else
> - bdi_writeback_all(sb, 0);
> + bdi_writeback_all(sb, 0, wbc->sync_mode);
>
> if (wbc->sync_mode == WB_SYNC_ALL) {
> struct inode *inode, *old_inode = NULL;
> diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
> index 7c2874f..0b20d4b 100644
> --- a/include/linux/backing-dev.h
> +++ b/include/linux/backing-dev.h
> @@ -15,6 +15,7 @@
> #include <linux/fs.h>
> #include <linux/sched.h>
> #include <linux/srcu.h>
> +#include <linux/writeback.h>
> #include <asm/atomic.h>
>
> struct page;
> @@ -60,7 +61,6 @@ struct bdi_writeback {
> #define BDI_MAX_FLUSHERS 32
>
> struct backing_dev_info {
> - struct rcu_head rcu_head;
> struct srcu_struct srcu; /* for wb_list read side protection */
> struct list_head bdi_list;
> unsigned long ra_pages; /* max readahead in PAGE_CACHE_SIZE units */
> @@ -105,14 +105,15 @@ int bdi_register(struct backing_dev_info *bdi, struct device *parent,
> int bdi_register_dev(struct backing_dev_info *bdi, dev_t dev);
> void bdi_unregister(struct backing_dev_info *bdi);
> int bdi_start_writeback(struct backing_dev_info *bdi, struct super_block *sb,
> - long nr_pages);
> + long nr_pages, enum writeback_sync_modes sync_mode);
> int bdi_writeback_task(struct bdi_writeback *wb);
> -void bdi_writeback_all(struct super_block *sb, long nr_pages);
> +void bdi_writeback_all(struct super_block *sb, long nr_pages,
> + enum writeback_sync_modes sync_mode);
> void bdi_add_default_flusher_task(struct backing_dev_info *bdi);
> void bdi_add_flusher_task(struct backing_dev_info *bdi);
> int bdi_has_dirty_io(struct backing_dev_info *bdi);
>
> -extern spinlock_t bdi_lock;
> +extern struct mutex bdi_lock;
> extern struct list_head bdi_list;
>
> static inline int wb_is_default_task(struct bdi_writeback *wb)
> diff --git a/mm/backing-dev.c b/mm/backing-dev.c
> index 60578bc..3ce3b57 100644
> --- a/mm/backing-dev.c
> +++ b/mm/backing-dev.c
> @@ -26,7 +26,7 @@ struct backing_dev_info default_backing_dev_info = {
> EXPORT_SYMBOL_GPL(default_backing_dev_info);
>
> static struct class *bdi_class;
> -DEFINE_SPINLOCK(bdi_lock);
> +DEFINE_MUTEX(bdi_lock);
> LIST_HEAD(bdi_list);
> LIST_HEAD(bdi_pending_list);
>
> @@ -360,14 +360,15 @@ static int bdi_start_fn(void *ptr)
> * Clear pending bit and wakeup anybody waiting to tear us down
> */
> clear_bit(BDI_pending, &bdi->state);
> + smp_mb__after_clear_bit();
> wake_up_bit(&bdi->state, BDI_pending);
>
> /*
> * Make us discoverable on the bdi_list again
> */
> - spin_lock_bh(&bdi_lock);
> - list_add_tail_rcu(&bdi->bdi_list, &bdi_list);
> - spin_unlock_bh(&bdi_lock);
> + mutex_lock(&bdi_lock);
> + list_add_tail(&bdi->bdi_list, &bdi_list);
> + mutex_unlock(&bdi_lock);
>
> ret = bdi_writeback_task(wb);
>
> @@ -419,15 +420,9 @@ static int bdi_forker_task(void *ptr)
> bdi_task_init(me->bdi, me);
>
> for (;;) {
> - struct backing_dev_info *bdi;
> + struct backing_dev_info *bdi, *tmp;
> struct bdi_writeback *wb;
>
> - prepare_to_wait(&me->wait, &wait, TASK_INTERRUPTIBLE);
> -
> - smp_mb();
> - if (list_empty(&bdi_pending_list))
> - schedule();
> -
> /*
> * Ideally we'd like not to see any dirty inodes on the
> * default_backing_dev_info. Until these are tracked down,
> @@ -438,19 +433,39 @@ static int bdi_forker_task(void *ptr)
> if (wb_has_dirty_io(me) || !list_empty(&me->bdi->work_list))
> wb_do_writeback(me);
>
> + prepare_to_wait(&me->wait, &wait, TASK_INTERRUPTIBLE);
> +
> + mutex_lock(&bdi_lock);
> +
> + /*
> + * Check if any existing bdi's have dirty data without
> + * a thread registered. If so, set that up.
> + */
> + list_for_each_entry_safe(bdi, tmp, &bdi_list, bdi_list) {
> + if (!list_empty(&bdi->wb_list) ||
> + !bdi_has_dirty_io(bdi))
> + continue;
> +
> + bdi_add_default_flusher_task(bdi);
> + }
> +
> + if (list_empty(&bdi_pending_list)) {
> + unsigned long wait;
> +
> + mutex_unlock(&bdi_lock);
> + wait = msecs_to_jiffies(dirty_writeback_interval * 10);
> + schedule_timeout(wait);
> + continue;
> + }
> +
> /*
> * This is our real job - check for pending entries in
> * bdi_pending_list, and create the tasks that got added
> */
> -repeat:
> - bdi = NULL;
> - spin_lock_bh(&bdi_lock);
> - if (!list_empty(&bdi_pending_list)) {
> - bdi = list_entry(bdi_pending_list.next,
> + bdi = list_entry(bdi_pending_list.next,
> struct backing_dev_info, bdi_list);
> - list_del_init(&bdi->bdi_list);
> - }
> - spin_unlock_bh(&bdi_lock);
> + list_del_init(&bdi->bdi_list);
> + mutex_unlock(&bdi_lock);
>
> if (!bdi)
> continue;
> @@ -475,12 +490,11 @@ readd_flush:
> * a chance to flush other bdi's to free
> * memory.
> */
> - spin_lock_bh(&bdi_lock);
> + mutex_lock(&bdi_lock);
> list_add_tail(&bdi->bdi_list, &bdi_pending_list);
> - spin_unlock_bh(&bdi_lock);
> + mutex_unlock(&bdi_lock);
>
> bdi_flush_io(bdi);
> - goto repeat;
> }
> }
>
> @@ -489,25 +503,8 @@ readd_flush:
> }
>
> /*
> - * Grace period has now ended, init bdi->bdi_list and add us to the
> - * list of bdi's that are pending for task creation. Wake up
> - * bdi_forker_task() to finish the job and add us back to the
> - * active bdi_list.
> + * bdi_lock held on entry
> */
> -static void bdi_add_to_pending(struct rcu_head *head)
> -{
> - struct backing_dev_info *bdi;
> -
> - bdi = container_of(head, struct backing_dev_info, rcu_head);
> - INIT_LIST_HEAD(&bdi->bdi_list);
> -
> - spin_lock(&bdi_lock);
> - list_add_tail(&bdi->bdi_list, &bdi_pending_list);
> - spin_unlock(&bdi_lock);
> -
> - wake_up(&default_backing_dev_info.wb.wait);
> -}
> -
> static void bdi_add_one_flusher_task(struct backing_dev_info *bdi,
> int(*func)(struct backing_dev_info *))
> {
> @@ -526,24 +523,22 @@ static void bdi_add_one_flusher_task(struct backing_dev_info *bdi,
> * waiting for previous additions to finish.
> */
> if (!func(bdi)) {
> - spin_lock_bh(&bdi_lock);
> - list_del_rcu(&bdi->bdi_list);
> - spin_unlock_bh(&bdi_lock);
> + list_move_tail(&bdi->bdi_list, &bdi_pending_list);
>
> /*
> - * We need to wait for the current grace period to end,
> - * in case others were browsing the bdi_list as well.
> - * So defer the adding and wakeup to after the RCU
> - * grace period has ended.
> + * We are now on the pending list, wake up bdi_forker_task()
> + * to finish the job and add us abck to the active bdi_list
> */
> - call_rcu(&bdi->rcu_head, bdi_add_to_pending);
> + wake_up(&default_backing_dev_info.wb.wait);
> }
> }
>
> static int flusher_add_helper_block(struct backing_dev_info *bdi)
> {
> + mutex_unlock(&bdi_lock);
> wait_on_bit_lock(&bdi->state, BDI_pending, bdi_sched_wait,
> TASK_UNINTERRUPTIBLE);
> + mutex_lock(&bdi_lock);
> return 0;
> }
>
> @@ -571,7 +566,9 @@ void bdi_add_default_flusher_task(struct backing_dev_info *bdi)
> */
> void bdi_add_flusher_task(struct backing_dev_info *bdi)
> {
> + mutex_lock(&bdi_lock);
> bdi_add_one_flusher_task(bdi, flusher_add_helper_block);
> + mutex_unlock(&bdi_lock);
> }
> EXPORT_SYMBOL(bdi_add_flusher_task);
>
> @@ -593,6 +590,14 @@ int bdi_register(struct backing_dev_info *bdi, struct device *parent,
> goto exit;
> }
>
> + mutex_lock(&bdi_lock);
> + list_add_tail(&bdi->bdi_list, &bdi_list);
> + mutex_unlock(&bdi_lock);
> +
> + bdi->dev = dev;
> + bdi_debug_register(bdi, dev_name(dev));
> + set_bit(BDI_registered, &bdi->state);
> +
> /*
> * Just start the forker thread for our default backing_dev_info,
> * and add other bdi's to the list. They will get a thread created
> @@ -616,14 +621,6 @@ int bdi_register(struct backing_dev_info *bdi, struct device *parent,
> }
> }
>
> - spin_lock_bh(&bdi_lock);
> - list_add_tail_rcu(&bdi->bdi_list, &bdi_list);
> - spin_unlock_bh(&bdi_lock);
> -
> - bdi->dev = dev;
> - bdi_debug_register(bdi, dev_name(dev));
> - set_bit(BDI_registered, &bdi->state);
> -
> exit:
> return ret;
> }
> @@ -655,15 +652,9 @@ static void bdi_wb_shutdown(struct backing_dev_info *bdi)
> /*
> * Make sure nobody finds us on the bdi_list anymore
> */
> - spin_lock_bh(&bdi_lock);
> - list_del_rcu(&bdi->bdi_list);
> - spin_unlock_bh(&bdi_lock);
> -
> - /*
> - * Now make sure that anybody who is currently looking at us from
> - * the bdi_list iteration have exited.
> - */
> - synchronize_rcu();
> + mutex_lock(&bdi_lock);
> + list_del(&bdi->bdi_list);
> + mutex_unlock(&bdi_lock);
>
> /*
> * Finally, kill the kernel threads. We don't need to be RCU
> @@ -689,7 +680,6 @@ int bdi_init(struct backing_dev_info *bdi)
> {
> int i, err;
>
> - INIT_RCU_HEAD(&bdi->rcu_head);
> bdi->dev = NULL;
>
> bdi->min_ratio = 0;
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index de3178a..7dd7de7 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -313,9 +313,8 @@ static unsigned int bdi_min_ratio;
> int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
> {
> int ret = 0;
> - unsigned long flags;
>
> - spin_lock_irqsave(&bdi_lock, flags);
> + mutex_lock(&bdi_lock);
> if (min_ratio > bdi->max_ratio) {
> ret = -EINVAL;
> } else {
> @@ -327,27 +326,26 @@ int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
> ret = -EINVAL;
> }
> }
> - spin_unlock_irqrestore(&bdi_lock, flags);
> + mutex_unlock(&bdi_lock);
>
> return ret;
> }
>
> int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio)
> {
> - unsigned long flags;
> int ret = 0;
>
> if (max_ratio > 100)
> return -EINVAL;
>
> - spin_lock_irqsave(&bdi_lock, flags);
> + mutex_lock(&bdi_lock);
> if (bdi->min_ratio > max_ratio) {
> ret = -EINVAL;
> } else {
> bdi->max_ratio = max_ratio;
> bdi->max_prop_frac = (PROP_FRAC_BASE * max_ratio) / 100;
> }
> - spin_unlock_irqrestore(&bdi_lock, flags);
> + mutex_unlock(&bdi_lock);
>
> return ret;
> }
> @@ -581,7 +579,7 @@ static void balance_dirty_pages(struct address_space *mapping)
> (!laptop_mode && (global_page_state(NR_FILE_DIRTY)
> + global_page_state(NR_UNSTABLE_NFS)
> > background_thresh)))
> - bdi_start_writeback(bdi, NULL, 0);
> + bdi_start_writeback(bdi, NULL, 0, WB_SYNC_NONE);
> }
>
> void set_page_dirty_balance(struct page *page, int page_mkwrite)
> @@ -674,7 +672,7 @@ void wakeup_flusher_threads(long nr_pages)
> if (nr_pages == 0)
> nr_pages = global_page_state(NR_FILE_DIRTY) +
> global_page_state(NR_UNSTABLE_NFS);
> - bdi_writeback_all(NULL, nr_pages);
> + bdi_writeback_all(NULL, nr_pages, WB_SYNC_NONE);
> }
>
> static void laptop_timer_fn(unsigned long unused);
>
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