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Subject: Re: [f2fs-dev] [PATCH] f2fs: remove a waiter for checkpoint
 completion
To:     Jaegeuk Kim <jaegeuk@kernel.org>, <linux-kernel@vger.kernel.org>,
        <linux-f2fs-devel@lists.sourceforge.net>, <kernel-team@android.com>
CC:     Eric Biggers <ebiggers@kernel.org>
References: <20200803172825.4077289-1-jaegeuk@kernel.org>
From:   Chao Yu <yuchao0@huawei.com>
Message-ID: <9638d2c5-cfd0-359f-187a-8e23bc6d822d@huawei.com>
Date:   Tue, 4 Aug 2020 08:55:55 +0800
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On 2020/8/4 1:28, Jaegeuk Kim wrote:
> It doesn't need to wait for checkpoint being completed triggered by end_io.
> 
> [   20.157753] ------------[ cut here ]------------
> [   20.158393] do not call blocking ops when !TASK_RUNNING; state=2 set at [<0000000096354225>] prepare_to_wait+0xcd/0x430
> [   20.159858] WARNING: CPU: 1 PID: 1152 at kernel/sched/core.c:7142 __might_sleep+0x149/0x1a0
> ...
> [   20.176110]  __submit_merged_write_cond+0x191/0x310
> [   20.176739]  f2fs_submit_merged_write+0x18/0x20
> [   20.177323]  f2fs_wait_on_all_pages+0x269/0x2d0
> [   20.177899]  ? block_operations+0x980/0x980
> [   20.178441]  ? __kasan_check_read+0x11/0x20
> [   20.178975]  ? finish_wait+0x260/0x260
> [   20.179488]  ? percpu_counter_set+0x147/0x230
> [   20.180049]  do_checkpoint+0x1757/0x2a50
> [   20.180558]  f2fs_write_checkpoint+0x840/0xaf0
> [   20.181126]  f2fs_sync_fs+0x287/0x4a0
> 
> Reported-by: Eric Biggers <ebiggers@kernel.org>
> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
> ---
>   fs/f2fs/checkpoint.c | 6 +-----
>   fs/f2fs/data.c       | 4 ----
>   fs/f2fs/f2fs.h       | 1 -
>   fs/f2fs/super.c      | 1 -
>   4 files changed, 1 insertion(+), 11 deletions(-)
> 
> diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
> index 99c8061da55b9..2bdddc725e677 100644
> --- a/fs/f2fs/checkpoint.c
> +++ b/fs/f2fs/checkpoint.c
> @@ -1255,11 +1255,7 @@ static void unblock_operations(struct f2fs_sb_info *sbi)
>   
>   void f2fs_wait_on_all_pages(struct f2fs_sb_info *sbi, int type)
>   {
> -	DEFINE_WAIT(wait);
> -
>   	for (;;) {
> -		prepare_to_wait(&sbi->cp_wait, &wait, TASK_UNINTERRUPTIBLE);

Wouldn't that case high cpu usage before io end?

> -
>   		if (!get_pages(sbi, type))
>   			break;
>   
> @@ -1271,9 +1267,9 @@ void f2fs_wait_on_all_pages(struct f2fs_sb_info *sbi, int type)
>   							FS_CP_META_IO);
>   		else if (type == F2FS_WB_CP_DATA)
>   			f2fs_submit_merged_write(sbi, DATA);
> +
>   		io_schedule_timeout(DEFAULT_IO_TIMEOUT);
>   	}
> -	finish_wait(&sbi->cp_wait, &wait);
>   }
>   
>   static void update_ckpt_flags(struct f2fs_sb_info *sbi, struct cp_control *cpc)
> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> index c1b676be67b9a..588d2871bbe69 100644
> --- a/fs/f2fs/data.c
> +++ b/fs/f2fs/data.c
> @@ -383,10 +383,6 @@ static void f2fs_write_end_io(struct bio *bio)
>   		clear_cold_data(page);
>   		end_page_writeback(page);
>   	}
> -	if (!get_pages(sbi, F2FS_WB_CP_DATA) &&
> -				wq_has_sleeper(&sbi->cp_wait))
> -		wake_up(&sbi->cp_wait);
> -
>   	bio_put(bio);
>   }
>   
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> index 02811ce15059b..a036539363030 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -1437,7 +1437,6 @@ struct f2fs_sb_info {
>   	struct rw_semaphore cp_rwsem;		/* blocking FS operations */
>   	struct rw_semaphore node_write;		/* locking node writes */
>   	struct rw_semaphore node_change;	/* locking node change */
> -	wait_queue_head_t cp_wait;
>   	unsigned long last_time[MAX_TIME];	/* to store time in jiffies */
>   	long interval_time[MAX_TIME];		/* to store thresholds */
>   
> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
> index 83bf9a02f83f2..5f4d9abc079d6 100644
> --- a/fs/f2fs/super.c
> +++ b/fs/f2fs/super.c
> @@ -3540,7 +3540,6 @@ static int f2fs_fill_super(struct super_block *sb, void *data, int silent)
>   
>   	init_rwsem(&sbi->cp_rwsem);
>   	init_rwsem(&sbi->quota_sem);
> -	init_waitqueue_head(&sbi->cp_wait);
>   	init_sb_info(sbi);
>   
>   	err = init_percpu_info(sbi);
>