RE: [f2fs-dev] [PATCH] f2fs: reduce competition among node page writes

[Chao Yu <chao2.yu@samsung.com>]

Hi Jaegeuk Changman,

> -----Original Message-----
> From: Chao Yu [mailto:chao2.yu@samsung.com]
> Sent: Thursday, July 03, 2014 6:59 PM
> To: Jaegeuk Kim; Changman Lee
> Cc: linux-fsdevel@vger.kernel.org; linux-kernel@vger.kernel.org;
> linux-f2fs-devel@lists.sourceforge.net
> Subject: [f2fs-dev] [PATCH] f2fs: reduce competition among node page writes
> 
> We do not need to block on ->node_write among different node page writers e.g.
> fsync/flush, unless we have a node page writer from write_checkpoint.
> So it's better use rw_semaphore instead of mutex type for ->node_write to
> promote performance.

If you could have time to help explaining the problem of this patch, I will be
appreciated for that.

Another question is what is ->writepages in sbi used for? I'm not quite clear.

Thanks,

> 
> Signed-off-by: Chao Yu <chao2.yu@samsung.com>
> ---
>  fs/f2fs/checkpoint.c |    6 +++---
>  fs/f2fs/f2fs.h       |    2 +-
>  fs/f2fs/node.c       |    4 ++--
>  fs/f2fs/super.c      |    2 +-
>  4 files changed, 7 insertions(+), 7 deletions(-)
> 
> diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
> index 0b4710c..eec406b 100644
> --- a/fs/f2fs/checkpoint.c
> +++ b/fs/f2fs/checkpoint.c
> @@ -714,10 +714,10 @@ retry_flush_dents:
>  	 * until finishing nat/sit flush.
>  	 */
>  retry_flush_nodes:
> -	mutex_lock(&sbi->node_write);
> +	down_write(&sbi->node_write);
> 
>  	if (get_pages(sbi, F2FS_DIRTY_NODES)) {
> -		mutex_unlock(&sbi->node_write);
> +		up_write(&sbi->node_write);
>  		sync_node_pages(sbi, 0, &wbc);
>  		goto retry_flush_nodes;
>  	}
> @@ -726,7 +726,7 @@ retry_flush_nodes:
> 
>  static void unblock_operations(struct f2fs_sb_info *sbi)
>  {
> -	mutex_unlock(&sbi->node_write);
> +	up_write(&sbi->node_write);
>  	f2fs_unlock_all(sbi);
>  }
> 
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> index ae3b4ac..ca30b5a 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -444,7 +444,7 @@ struct f2fs_sb_info {
>  	struct inode *meta_inode;		/* cache meta blocks */
>  	struct mutex cp_mutex;			/* checkpoint procedure lock */
>  	struct rw_semaphore cp_rwsem;		/* blocking FS operations */
> -	struct mutex node_write;		/* locking node writes */
> +	struct rw_semaphore node_write;		/* locking node writes */
>  	struct mutex writepages;		/* mutex for writepages() */
>  	bool por_doing;				/* recovery is doing or not */
>  	wait_queue_head_t cp_wait;
> diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
> index a90f51d..7b5b5de 100644
> --- a/fs/f2fs/node.c
> +++ b/fs/f2fs/node.c
> @@ -1231,12 +1231,12 @@ static int f2fs_write_node_page(struct page *page,
>  	if (wbc->for_reclaim)
>  		goto redirty_out;
> 
> -	mutex_lock(&sbi->node_write);
> +	down_read(&sbi->node_write);
>  	set_page_writeback(page);
>  	write_node_page(sbi, page, &fio, nid, ni.blk_addr, &new_addr);
>  	set_node_addr(sbi, &ni, new_addr, is_fsync_dnode(page));
>  	dec_page_count(sbi, F2FS_DIRTY_NODES);
> -	mutex_unlock(&sbi->node_write);
> +	up_read(&sbi->node_write);
>  	unlock_page(page);
>  	return 0;
> 
> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
> index 8f96d93..bed9413 100644
> --- a/fs/f2fs/super.c
> +++ b/fs/f2fs/super.c
> @@ -947,7 +947,7 @@ static int f2fs_fill_super(struct super_block *sb, void *data, int silent)
>  	mutex_init(&sbi->gc_mutex);
>  	mutex_init(&sbi->writepages);
>  	mutex_init(&sbi->cp_mutex);
> -	mutex_init(&sbi->node_write);
> +	init_rwsem(&sbi->node_write);
>  	sbi->por_doing = false;
>  	spin_lock_init(&sbi->stat_lock);
> 
> --
> 1.7.9.5
> 
> 
> 
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