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Date:   Thu, 11 May 2017 11:36:00 -0700
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Chao Yu <chao@...nel.org>
Cc:     linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, Chao Yu <yuchao0@...wei.com>
Subject: Re: [PATCH 3/3] f2fs: introduce io_list for serialize data/node IOs

Hi Chao,

On 05/09, Chao Yu wrote:
> From: Chao Yu <yuchao0@...wei.com>
> 
> Serialize data/node IOs by using fifo list instead of mutex lock,
> it will help to enhance concurrency of f2fs, meanwhile keeping LFS
> IO semantics.

I'm not against to give it a try, but not sure how much we can get a benefit
from this approach frankly. Have you got a trouble on any lock contention from
the below io_rwsem or mutex?

Thanks,

> 
> Signed-off-by: Chao Yu <yuchao0@...wei.com>
> ---
>  fs/f2fs/checkpoint.c |  1 +
>  fs/f2fs/data.c       | 28 ++++++++++++++++++++++++----
>  fs/f2fs/f2fs.h       |  5 ++++-
>  fs/f2fs/gc.c         |  3 ++-
>  fs/f2fs/segment.c    | 20 ++++++++++++++------
>  fs/f2fs/segment.h    |  3 ++-
>  6 files changed, 47 insertions(+), 13 deletions(-)
> 
> diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
> index 2a475e83a092..7b3393474f6b 100644
> --- a/fs/f2fs/checkpoint.c
> +++ b/fs/f2fs/checkpoint.c
> @@ -162,6 +162,7 @@ int ra_meta_pages(struct f2fs_sb_info *sbi, block_t start, int nrpages,
>  		.op = REQ_OP_READ,
>  		.op_flags = sync ? (REQ_META | REQ_PRIO) : REQ_RAHEAD,
>  		.encrypted_page = NULL,
> +		.in_list = false,
>  	};
>  	struct blk_plug plug;
>  
> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> index 5f001b471252..89eaa8aaa97b 100644
> --- a/fs/f2fs/data.c
> +++ b/fs/f2fs/data.c
> @@ -393,10 +393,28 @@ int f2fs_submit_page_mbio(struct f2fs_io_info *fio)
>  	struct f2fs_bio_info *io;
>  	bool is_read = is_read_io(fio->op);
>  	struct page *bio_page;
> +	struct curseg_info *curseg;
>  	int err = 0;
>  
> +	if (fio->in_list)
> +		curseg = CURSEG_I(sbi, fio->seg_type);
> +
>  	io = __get_bio_info(sbi, fio->op, fio->type, fio->seg_type);
>  
> +	down_write(&io->io_rwsem);
> +next:
> +	if (fio->in_list) {
> +		spin_lock(&curseg->io_lock);
> +		if (list_empty(&curseg->io_list)) {
> +			spin_unlock(&curseg->io_lock);
> +			goto out_fail;
> +		}
> +		fio = list_first_entry(&curseg->io_list,
> +						struct f2fs_io_info, list);
> +		list_del(&fio->list);
> +		spin_unlock(&curseg->io_lock);
> +	}
> +
>  	if (fio->old_blkaddr != NEW_ADDR)
>  		verify_block_addr(sbi, fio->old_blkaddr);
>  	verify_block_addr(sbi, fio->new_blkaddr);
> @@ -409,8 +427,6 @@ int f2fs_submit_page_mbio(struct f2fs_io_info *fio)
>  	if (!is_read)
>  		inc_page_count(sbi, WB_DATA_TYPE(bio_page));
>  
> -	down_write(&io->io_rwsem);
> -
>  	if (io->bio && (io->last_block_in_bio != fio->new_blkaddr - 1 ||
>  	    (io->fio.op != fio->op || io->fio.op_flags != fio->op_flags) ||
>  			!__same_bdev(sbi, fio->new_blkaddr, io->bio)))
> @@ -437,9 +453,13 @@ int f2fs_submit_page_mbio(struct f2fs_io_info *fio)
>  
>  	io->last_block_in_bio = fio->new_blkaddr;
>  	f2fs_trace_ios(fio, 0);
> +
> +	trace_f2fs_submit_page_mbio(fio->page, fio);
> +
> +	if (fio->in_list)
> +		goto next;
>  out_fail:
>  	up_write(&io->io_rwsem);
> -	trace_f2fs_submit_page_mbio(fio->page, fio);
>  	return err;
>  }
>  
> @@ -752,7 +772,7 @@ static int __allocate_data_block(struct dnode_of_data *dn)
>  	set_summary(&sum, dn->nid, dn->ofs_in_node, ni.version);
>  
>  	allocate_data_block(sbi, NULL, dn->data_blkaddr, &dn->data_blkaddr,
> -						&sum, CURSEG_WARM_DATA);
> +					&sum, CURSEG_WARM_DATA, NULL, false);
>  	set_data_blkaddr(dn);
>  
>  	/* update i_size */
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> index 9129a6229bc8..6b8e9f051aa2 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -802,8 +802,10 @@ struct f2fs_io_info {
>  	block_t old_blkaddr;	/* old block address before Cow */
>  	struct page *page;	/* page to be written */
>  	struct page *encrypted_page;	/* encrypted page */
> +	struct list_head list;		/* serialize IOs */
>  	bool submitted;		/* indicate IO submission */
>  	bool need_lock;		/* indicate we need to lock cp_rwsem */
> +	bool in_list;		/* indicate fio is in io_list */
>  };
>  
>  #define is_read_io(rw) ((rw) == READ)
> @@ -2274,7 +2276,8 @@ void f2fs_replace_block(struct f2fs_sb_info *sbi, struct dnode_of_data *dn,
>  			bool recover_newaddr);
>  void allocate_data_block(struct f2fs_sb_info *sbi, struct page *page,
>  			block_t old_blkaddr, block_t *new_blkaddr,
> -			struct f2fs_summary *sum, int type);
> +			struct f2fs_summary *sum, int type,
> +			struct f2fs_io_info *fio, bool add_list);
>  void f2fs_wait_on_page_writeback(struct page *page,
>  			enum page_type type, bool ordered);
>  void f2fs_wait_on_encrypted_page_writeback(struct f2fs_sb_info *sbi,
> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
> index 8b267ca30926..ac2f74e40eea 100644
> --- a/fs/f2fs/gc.c
> +++ b/fs/f2fs/gc.c
> @@ -590,6 +590,7 @@ static void move_encrypted_block(struct inode *inode, block_t bidx,
>  		.op = REQ_OP_READ,
>  		.op_flags = 0,
>  		.encrypted_page = NULL,
> +		.in_list = false,
>  	};
>  	struct dnode_of_data dn;
>  	struct f2fs_summary sum;
> @@ -633,7 +634,7 @@ static void move_encrypted_block(struct inode *inode, block_t bidx,
>  	fio.new_blkaddr = fio.old_blkaddr = dn.data_blkaddr;
>  
>  	allocate_data_block(fio.sbi, NULL, fio.old_blkaddr, &newaddr,
> -							&sum, fio.seg_type);
> +					&sum, fio.seg_type, NULL, false);
>  
>  	fio.encrypted_page = pagecache_get_page(META_MAPPING(fio.sbi), newaddr,
>  					FGP_LOCK | FGP_CREAT, GFP_NOFS);
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index c047b5d8b9d3..d4975b8f4620 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -2100,7 +2100,8 @@ static int __get_segment_type(struct page *page, enum page_type p_type)
>  
>  void allocate_data_block(struct f2fs_sb_info *sbi, struct page *page,
>  		block_t old_blkaddr, block_t *new_blkaddr,
> -		struct f2fs_summary *sum, int type)
> +		struct f2fs_summary *sum, int type,
> +		struct f2fs_io_info *fio, bool add_list)
>  {
>  	struct sit_info *sit_i = SIT_I(sbi);
>  	struct curseg_info *curseg = CURSEG_I(sbi, type);
> @@ -2136,6 +2137,14 @@ void allocate_data_block(struct f2fs_sb_info *sbi, struct page *page,
>  	if (page && IS_NODESEG(type))
>  		fill_node_footer_blkaddr(page, NEXT_FREE_BLKADDR(sbi, curseg));
>  
> +	if (add_list) {
> +		INIT_LIST_HEAD(&fio->list);
> +		fio->in_list = true;
> +		spin_lock(&curseg->io_lock);
> +		list_add_tail(&fio->list, &curseg->io_list);
> +		spin_unlock(&curseg->io_lock);
> +	}
> +
>  	mutex_unlock(&curseg->curseg_mutex);
>  }
>  
> @@ -2145,10 +2154,9 @@ static void do_write_page(struct f2fs_summary *sum, struct f2fs_io_info *fio)
>  
>  	fio->seg_type = __get_segment_type(fio->page, fio->type);
>  
> -	mutex_lock(&CURSEG_I(fio->sbi, fio->seg_type)->wio_mutex);
>  reallocate:
>  	allocate_data_block(fio->sbi, fio->page, fio->old_blkaddr,
> -					&fio->new_blkaddr, sum, fio->seg_type);
> +			&fio->new_blkaddr, sum, fio->seg_type, fio, true);
>  
>  	/* writeout dirty page into bdev */
>  	err = f2fs_submit_page_mbio(fio);
> @@ -2156,8 +2164,6 @@ static void do_write_page(struct f2fs_summary *sum, struct f2fs_io_info *fio)
>  		fio->old_blkaddr = fio->new_blkaddr;
>  		goto reallocate;
>  	}
> -
> -	mutex_unlock(&CURSEG_I(fio->sbi, fio->seg_type)->wio_mutex);
>  }
>  
>  void write_meta_page(struct f2fs_sb_info *sbi, struct page *page)
> @@ -2171,6 +2177,7 @@ void write_meta_page(struct f2fs_sb_info *sbi, struct page *page)
>  		.new_blkaddr = page->index,
>  		.page = page,
>  		.encrypted_page = NULL,
> +		.in_list = false,
>  	};
>  
>  	if (unlikely(page->index >= MAIN_BLKADDR(sbi)))
> @@ -2978,7 +2985,8 @@ static int build_curseg(struct f2fs_sb_info *sbi)
>  		array[i].bio_info.sbi = sbi;
>  		array[i].bio_info.bio = NULL;
>  
> -		mutex_init(&array[i].wio_mutex);
> +		spin_lock_init(&array[i].io_lock);
> +		INIT_LIST_HEAD(&array[i].io_list);
>  	}
>  	return restore_curseg_summaries(sbi);
>  }
> diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
> index 701944b462cd..b6f5dffeaa61 100644
> --- a/fs/f2fs/segment.h
> +++ b/fs/f2fs/segment.h
> @@ -283,7 +283,8 @@ struct curseg_info {
>  	struct rw_semaphore journal_rwsem;	/* protect journal area */
>  	struct f2fs_journal *journal;		/* cached journal info */
>  	struct f2fs_bio_info bio_info;		/* for log bios */
> -	struct mutex wio_mutex;			/* serialize DATA/NODE IOs */
> +	spinlock_t io_lock;			/* serialize DATA/NODE IOs */
> +	struct list_head io_list;		/* tracking fios */
>  	unsigned char alloc_type;		/* current allocation type */
>  	unsigned int segno;			/* current segment number */
>  	unsigned short next_blkoff;		/* next block offset to write */
> -- 
> 2.12.2.575.gb14f27f

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