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Date:	Mon, 10 Mar 2014 13:09:48 +0900
From:	Changman Lee <cm224.lee@...sung.com>
To:	Gu Zheng <guz.fnst@...fujitsu.com>
Cc:	Kim <jaegeuk.kim@...sung.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	f2fs <linux-f2fs-devel@...ts.sourceforge.net>
Subject: Re: [f2fs-dev] [PATCH 5/5] f2fs: add a wait queue to avoid
 unnecessary, build_free_nid

On 금, 2014-03-07 at 18:43 +0800, Gu Zheng wrote:
> Previously, when we try to alloc free nid while the build free nid
> is going, the allocer will be run into the flow that waiting for
> "nm_i->build_lock", see following:
> 	/* We should not use stale free nids created by build_free_nids */
> ---->	if (nm_i->fcnt && !on_build_free_nids(nm_i)) {
> 		f2fs_bug_on(list_empty(&nm_i->free_nid_list));
> 		list_for_each(this, &nm_i->free_nid_list) {
> 			i = list_entry(this, struct free_nid, list);
> 			if (i->state == NID_NEW)
> 				break;
> 		}
> 
> 		f2fs_bug_on(i->state != NID_NEW);
> 		*nid = i->nid;
> 		i->state = NID_ALLOC;
> 		nm_i->fcnt--;
> 		spin_unlock(&nm_i->free_nid_list_lock);
> 		return true;
> 	}
> 	spin_unlock(&nm_i->free_nid_list_lock);
> 
> 	/* Let's scan nat pages and its caches to get free nids */
> ---->	mutex_lock(&nm_i->build_lock);
> 	build_free_nids(sbi);
> 	mutex_unlock(&nm_i->build_lock);
> and this will cause another unnecessary building free nid if the current
> building free nid job is done.
> So here we introduce a wait_queue to avoid this issue.
> 
> Signed-off-by: Gu Zheng <guz.fnst@...fujitsu.com>
> ---
>  fs/f2fs/f2fs.h |    1 +
>  fs/f2fs/node.c |   10 +++++++++-
>  2 files changed, 10 insertions(+), 1 deletions(-)
> 
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> index f845e92..7ae193e 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -256,6 +256,7 @@ struct f2fs_nm_info {
>  	spinlock_t free_nid_list_lock;	/* protect free nid list */
>  	unsigned int fcnt;		/* the number of free node id */
>  	struct mutex build_lock;	/* lock for build free nids */
> +	wait_queue_head_t build_wq;	/* wait queue for build free nids */
>  
>  	/* for checkpoint */
>  	char *nat_bitmap;		/* NAT bitmap pointer */
> diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
> index 4b7861d..ab44711 100644
> --- a/fs/f2fs/node.c
> +++ b/fs/f2fs/node.c
> @@ -1422,7 +1422,13 @@ retry:
>  	spin_lock(&nm_i->free_nid_list_lock);
>  
>  	/* We should not use stale free nids created by build_free_nids */
> -	if (nm_i->fcnt && !on_build_free_nids(nm_i)) {
> +	if (on_build_free_nids(nm_i)) {
> +		spin_unlock(&nm_i->free_nid_list_lock);
> +		wait_event(nm_i->build_wq, !on_build_free_nids(nm_i));
> +		goto retry;
> +	}
> +

It would be better moving spin_lock(free_nid_list_lock) here after
removing above spin_unlock().

> +	if (nm_i->fcnt) {
>  		f2fs_bug_on(list_empty(&nm_i->free_nid_list));
>  		list_for_each(this, &nm_i->free_nid_list) {
>  			i = list_entry(this, struct free_nid, list);
> @@ -1443,6 +1449,7 @@ retry:
>  	mutex_lock(&nm_i->build_lock);
>  	build_free_nids(sbi);
>  	mutex_unlock(&nm_i->build_lock);
> +	wake_up_all(&nm_i->build_wq);
>  	goto retry;
>  }
>  
> @@ -1813,6 +1820,7 @@ static int init_node_manager(struct f2fs_sb_info *sbi)
>  	INIT_LIST_HEAD(&nm_i->dirty_nat_entries);
>  
>  	mutex_init(&nm_i->build_lock);
> +	init_waitqueue_head(&nm_i->build_wq);
>  	spin_lock_init(&nm_i->free_nid_list_lock);
>  	rwlock_init(&nm_i->nat_tree_lock);
>  


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