[Devel] [RFC PATCH vz9 v6 33/62] dm-ploop: convert wb_batch_list to lockless variant

[Andrey Zhadchenko]

This should be merged with other writeback patches

On 12/5/24 22:56, Alexander Atanasov wrote:
> Merging required to back this change, so do it again.
> 
> Signed-off-by: Alexander Atanasov <alexander.atanasov at virtuozzo.com>
> ---
>   drivers/md/dm-ploop-map.c    | 49 ++++++++++++++++++------------------
>   drivers/md/dm-ploop-target.c |  1 -
>   drivers/md/dm-ploop.h        |  1 -
>   3 files changed, 25 insertions(+), 26 deletions(-)
> 
> diff --git a/drivers/md/dm-ploop-map.c b/drivers/md/dm-ploop-map.c
> index ad4fb84e913f..722a1fbf499e 100644
> --- a/drivers/md/dm-ploop-map.c
> +++ b/drivers/md/dm-ploop-map.c
> @@ -559,7 +559,7 @@ static bool ploop_md_make_dirty(struct ploop *ploop, struct md_page *md)
>   	WARN_ON_ONCE(test_bit(MD_WRITEBACK, &md->status));
>   	md->dirty_time = ktime_get();
>   	if (!test_and_set_bit(MD_DIRTY, &md->status)) {
> -		list_add(&md->wb_link, &ploop->wb_batch_list);
> +		llist_add((struct llist_node *)&md->wb_link, &ploop->wb_batch_llist);
>   		new = true;
>   	}
>   	write_unlock_irqrestore(&ploop->bat_rwlock, flags);
> @@ -1829,36 +1829,36 @@ static void ploop_submit_metadata_writeback(struct ploop *ploop)
>   {
>   	ktime_t ktime, ktimeout;
>   	LIST_HEAD(ll_skipped);
> -	struct md_page *md, *mtmp;
> +	struct md_page *md;
> +	struct llist_node *pos, *t;
> +	struct llist_node *ll_wb_batch;
>   
>   	ktime = ktime_get();
>   	ktimeout = ktime_add_ms(ktime, ploop->md_submit_delay_ms);
> +	/* Lock here to protect against md_inflight counting */
> +	write_lock_irq(&ploop->bat_rwlock);
> +	ll_wb_batch = llist_del_all(&ploop->wb_batch_llist);
> +	write_unlock_irq(&ploop->bat_rwlock);
>   	/*
>   	 * Pages are set dirty so no one must touch lists
>   	 * if new md entries are dirtied they are added at the start of the list
>   	 */
> -	list_for_each_entry_safe(md, mtmp, &ploop->wb_batch_list, wb_link) {
> -		write_lock_irq(&ploop->bat_rwlock);
> -		list_del_init(&md->wb_link);
> +	llist_for_each_safe(pos, t, ll_wb_batch) {
> +		md = list_entry((struct list_head *)pos, typeof(*md), wb_link);
> +		INIT_LIST_HEAD(&md->wb_link);
>   		if (md->high_prio || ktime_after(md->dirty_time, ktimeout)
>   		    || ploop->force_md_writeback) {
>   			/* L1L2 mustn't be redirtyed, when wb in-flight! */
>   			WARN_ON_ONCE(!test_bit(MD_DIRTY, &md->status));
>   			WARN_ON_ONCE(test_bit(MD_WRITEBACK, &md->status));
> +			md->high_prio = false;
>   			set_bit(MD_WRITEBACK, &md->status);
>   			clear_bit(MD_DIRTY, &md->status);
> -			md->high_prio = false;
> -			write_unlock_irq(&ploop->bat_rwlock);
>   			ploop_index_wb_submit(ploop, md->piwb);
>   		} else {
> -			list_add_tail(&md->wb_link, &ll_skipped);
> -			write_unlock_irq(&ploop->bat_rwlock);
> +			llist_add((struct llist_node *)&md->wb_link, &ploop->wb_batch_llist);
>   		}
>   	}
> -	write_lock_irq(&ploop->bat_rwlock);
> -	list_splice(&ll_skipped, &ploop->wb_batch_list);
> -	write_unlock_irq(&ploop->bat_rwlock);
> -
>   }
>   
>   static void process_ploop_fsync_work(struct ploop *ploop, struct llist_node *llflush_pios)
> @@ -1991,18 +1991,19 @@ static void ploop_preflush_endio(struct pio *pio, void *orig_pio_ptr,
>   	}
>   }
>   
> -static void ploop_prepare_flush(struct ploop *ploop, struct pio *pio)
> +static int ploop_prepare_flush(struct ploop *ploop, struct pio *pio)
>   {
>   	struct pio *flush_pio = pio;
>   	struct md_page *md, *n;
>   	int md_inflight = 0;
> +	struct llist_node *pos, *t;
>   
>   	if (pio->bi_op & REQ_PREFLUSH && (pio->bi_op & REQ_OP_MASK) != REQ_OP_FLUSH) {
>   		flush_pio = ploop_alloc_pio(ploop, GFP_NOIO);
>   		if (!flush_pio) {
>   			pio->bi_status = BLK_STS_RESOURCE;
>   			ploop_pio_endio(pio);
> -			return;
> +			return -1;
>   		}
>   
>   		ploop_init_pio(ploop, REQ_OP_FLUSH, flush_pio);
> @@ -2013,21 +2014,17 @@ static void ploop_prepare_flush(struct ploop *ploop, struct pio *pio)
>   	}
>   
>   	write_lock_irq(&ploop->bat_rwlock);
> -
> -	list_for_each_entry_safe(md, n, &ploop->wb_batch_list, wb_link) {
> +	llist_for_each_safe(pos, t, ploop->wb_batch_llist.first) {
> +		md = list_entry((struct list_head *)pos, typeof(*md), wb_link);
>   		md_inflight++;
>   		md->piwb->flush_pio = flush_pio;
>   		md->high_prio = true;
>   	}
>   
>   	atomic_set(&flush_pio->md_inflight, md_inflight);
> -
>   	write_unlock_irq(&ploop->bat_rwlock);
>   
> -	if (md_inflight)
> -		ploop_schedule_work(ploop);
> -	else
> -		ploop_dispatch_pios(ploop, flush_pio, NULL);
> +	return md_inflight;
>   }
>   
>   static void ploop_submit_embedded_pio(struct ploop *ploop, struct pio *pio)
> @@ -2056,8 +2053,12 @@ static void ploop_submit_embedded_pio(struct ploop *ploop, struct pio *pio)
>   	ploop_inc_nr_inflight(ploop, pio);
>   
>   	if ((pio->bi_op & REQ_OP_MASK) == REQ_OP_FLUSH || pio->bi_op & REQ_PREFLUSH) {
> -		ploop_prepare_flush(ploop, pio);
> -		return;
> +		ret = ploop_prepare_flush(ploop, pio);
> +		if (ret < 0)
> +			return;
> +		if (ret > 0)
> +			goto out;
> +		/* Will add to prepare list and schedule work */
>   	}
>   
>   	if (pio->queue_list_id == PLOOP_LIST_FLUSH) {
> diff --git a/drivers/md/dm-ploop-target.c b/drivers/md/dm-ploop-target.c
> index 0b691ff031e2..6c60043c0487 100644
> --- a/drivers/md/dm-ploop-target.c
> +++ b/drivers/md/dm-ploop-target.c
> @@ -437,7 +437,6 @@ static int ploop_ctr(struct dm_target *ti, unsigned int argc, char **argv)
>   
>   	INIT_LIST_HEAD(&ploop->cluster_lk_list);
>   	init_llist_head(&ploop->wb_batch_llist);
> -	INIT_LIST_HEAD(&ploop->wb_batch_list);
>   	ploop->last_md_submit = 0;
>   	ploop->md_submit_delay_ms = PLOOP_DEFAULT_METADATA_SUBMIT_DELAY;
>   
> diff --git a/drivers/md/dm-ploop.h b/drivers/md/dm-ploop.h
> index cdc1f9709a34..1ecd51f2ac3a 100644
> --- a/drivers/md/dm-ploop.h
> +++ b/drivers/md/dm-ploop.h
> @@ -179,7 +179,6 @@ struct ploop {
>   	rwlock_t bat_rwlock;
>   
>   	struct llist_head wb_batch_llist;
> -	struct list_head wb_batch_list;
>   
>   	ktime_t last_md_submit;
>   	bool	force_md_writeback;