Re: [f2fs-dev] [PATCH v1 04/12] f2fs: cache: introduce writeback thread

On 08/20, Chao Yu via Linux-f2fs-devel wrote:
> This patch introduces a background writeback kthread (f2fs_writeback-x:y)
> to periodically flush dirty metadata cache entries with a default
> interval of 5 seconds.
> 
> It manages thread lifecycle across mount, unmount, and remount (rw/ro)
> transitions, and hooks synchronous flushing into checkpoint commits.
> 
> Signed-off-by: Chao Yu <[email protected]>
> ---
>  fs/f2fs/cache.c      | 54 ++++++++++++++++++++++++++++++++++++++++++++
>  fs/f2fs/cache.h      | 13 +++++++++++
>  fs/f2fs/checkpoint.c |  1 +
>  fs/f2fs/f2fs.h       |  3 +++
>  fs/f2fs/super.c      | 31 ++++++++++++++++++++++++-
>  5 files changed, 101 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/f2fs/cache.c b/fs/f2fs/cache.c
> index c071364822c4..cb5b26046162 100644
> --- a/fs/f2fs/cache.c
> +++ b/fs/f2fs/cache.c
> @@ -611,3 +611,57 @@ unsigned long f2fs_shrink_cache(struct f2fs_sb_info *sbi,
>  {
>  	return f2fs_do_shrink_cache(META_CACHE(sbi), nr_to_scan);
>  }
> +
> +static int f2fs_cache_writeback_kthread(void *data)
> +{
> +	struct f2fs_sb_info *sbi = data;
> +	struct f2fs_cache_kthread *cache_thread = &sbi->cache_thread;
> +	wait_queue_head_t *wq = &cache_thread->cache_wb_wq;
> +	unsigned int interval = DEF_DIRTY_CACHE_TIMEOUT;
> +
> +	set_freezable();
> +
> +	while (!kthread_should_stop()) {
> +		wait_event_freezable_timeout(*wq,
> +				kthread_should_stop() ||
> +				cache_thread->cache_wb_task == NULL,
> +				msecs_to_jiffies(interval));
> +
> +		if (kthread_should_stop())
> +			break;
> +		if (f2fs_cp_error(sbi))
> +			continue;
> +	}
> +	return 0;
> +}
> +
> +int f2fs_start_cache_wb_thread(struct f2fs_sb_info *sbi)
> +{
> +	struct f2fs_cache_kthread *cache_thread = &sbi->cache_thread;
> +	dev_t dev = sbi->sb->s_dev;
> +	char name[36];
> +
> +	if (cache_thread->cache_wb_task)
> +		return 0;
> +
> +	init_waitqueue_head(&cache_thread->cache_wb_wq);
> +	snprintf(name, sizeof(name), "f2fs_writeback-%u:%u",
> +			MAJOR(dev), MINOR(dev));
> +
> +	cache_thread->cache_wb_task = kthread_run(f2fs_cache_writeback_kthread,
> +						sbi, "%s", name);
> +	if (IS_ERR(cache_thread->cache_wb_task))
> +		return PTR_ERR(cache_thread->cache_wb_task);
> +	return 0;
> +}
> +
> +void f2fs_stop_cache_wb_thread(struct f2fs_sb_info *sbi)
> +{
> +	struct f2fs_cache_kthread *cache_thread = &sbi->cache_thread;
> +
> +	if (!cache_thread->cache_wb_task)
> +		return;
> +
> +	kthread_stop(cache_thread->cache_wb_task);
> +	cache_thread->cache_wb_task = NULL;
> +}
> diff --git a/fs/f2fs/cache.h b/fs/f2fs/cache.h
> index d92b6f3ed585..5e9fe8c0b15c 100644
> --- a/fs/f2fs/cache.h
> +++ b/fs/f2fs/cache.h
> @@ -191,4 +191,17 @@ void f2fs_stop_cache_wb_thread(struct f2fs_sb_info *sbi);
>  unsigned long f2fs_shrink_cache(struct f2fs_sb_info *sbi,
>  				unsigned long nr_to_scan);
>  
> +#define DEF_DIRTY_CACHE_TIMEOUT 5000
> +
> +struct f2fs_cache_kthread {
> +	struct task_struct *cache_wb_task;
> +	wait_queue_head_t cache_wb_wq;
> +	atomic_t cache_wb_trigger;
> +	unsigned int cache_wb_interval_ms;
> +};
> +
> +int f2fs_start_cache_wb_thread(struct f2fs_sb_info *sbi);
> +void f2fs_stop_cache_wb_thread(struct f2fs_sb_info *sbi);
> +void f2fs_sync_cache_wb(struct f2fs_sb_info *sbi);
> +
>  #endif /* _LINUX_F2FS_CACHE_H */
> diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
> index f81ba8cc861a..729d19680caf 100644
> --- a/fs/f2fs/checkpoint.c
> +++ b/fs/f2fs/checkpoint.c
> @@ -1596,6 +1596,7 @@ static int block_operations(struct f2fs_sb_info *sbi)
>  	 * sbi->node_change is used only for AIO write_begin path which produces
>  	 * dirty node blocks and some checkpoint values by block allocation.
>  	 */
> +

Unnecessary line.

>  	__prepare_cp_block(sbi);
>  	f2fs_up_write(&sbi->node_change);
>  	return err;
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> index 9b7c60bbb137..6e20b3586f26 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -2108,6 +2108,9 @@ struct f2fs_sb_info {
>  
>  	/* f2fs internal cache */
>  	struct f2fs_cached_block_list meta_blocks;
> +
> +	/* internal cache flush thread */
> +	struct f2fs_cache_kthread cache_thread;
>  };
>  
>  /* Definitions to access f2fs_sb_info */
> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
> index bcfb1f97850e..89affe72f4fc 100644
> --- a/fs/f2fs/super.c
> +++ b/fs/f2fs/super.c
> @@ -1998,6 +1998,7 @@ static void f2fs_put_super(struct super_block *sb)
>  	 * flush all issued checkpoints and stop checkpoint issue thread.
>  	 * after then, all checkpoints should be done by each process context.
>  	 */
> +	f2fs_stop_cache_wb_thread(sbi);
>  	f2fs_stop_ckpt_thread(sbi);
>  
>  	/*
> @@ -2799,6 +2800,7 @@ static int __f2fs_remount(struct fs_context *fc, struct super_block *sb)
>  	unsigned int flags = fc->sb_flags;
>  	int err;
>  	bool need_restart_gc = false, need_stop_gc = false;
> +	bool need_restart_wb = false, need_stop_wb = false;
>  	bool need_restart_flush = false, need_stop_flush = false;
>  	bool need_restart_discard = false, need_stop_discard = false;
>  	bool need_enable_checkpoint = false, need_disable_checkpoint = false;
> @@ -2957,6 +2959,18 @@ static int __f2fs_remount(struct fs_context *fc, struct super_block *sb)
>  		need_stop_gc = true;
>  	}
>  
> +	if (flags & SB_RDONLY) {
> +		if (sbi->cache_thread.cache_wb_task) {
> +			f2fs_stop_cache_wb_thread(sbi);
> +			need_restart_wb = true;
> +		}
> +	} else if (!sbi->cache_thread.cache_wb_task) {
> +		err = f2fs_start_cache_wb_thread(sbi);
> +		if (err)
> +			goto restore_gc;
> +		need_stop_wb = true;
> +	}
> +
>  	if (flags & SB_RDONLY) {
>  		sync_inodes_sb(sb);
>  
> @@ -2979,7 +2993,7 @@ static int __f2fs_remount(struct fs_context *fc, struct super_block *sb)
>  	} else {
>  		err = f2fs_create_flush_cmd_control(sbi);
>  		if (err)
> -			goto restore_gc;
> +			goto restore_wb;
>  		need_stop_flush = true;
>  	}
>  
> @@ -3075,6 +3089,13 @@ static int __f2fs_remount(struct fs_context *fc, struct super_block *sb)
>  		clear_opt(sbi, FLUSH_MERGE);
>  		f2fs_destroy_flush_cmd_control(sbi, false);
>  	}
> +restore_wb:
> +	if (need_restart_wb) {
> +		if (f2fs_start_cache_wb_thread(sbi))
> +			f2fs_warn(sbi, "background cache writeback thread has stopped");
> +	} else if (need_stop_wb) {
> +		f2fs_stop_cache_wb_thread(sbi);
> +	}
>  restore_gc:
>  	if (need_restart_gc) {
>  		if (f2fs_start_gc_thread(sbi))
> @@ -5461,6 +5482,12 @@ static int f2fs_fill_super(struct super_block *sb, struct fs_context *fc)
>  			goto sync_free_meta;
>  	}
>  
> +	if (!f2fs_readonly(sb)) {
> +		err = f2fs_start_cache_wb_thread(sbi);
> +		if (err)
> +			goto stop_gc_thread;
> +	}
> +
>  	/* recover broken superblock */
>  	if (recovery) {
>  		err = f2fs_commit_super(sbi, true);
> @@ -5483,6 +5510,8 @@ static int f2fs_fill_super(struct super_block *sb, struct fs_context *fc)
>  	sbi->umount_lock_holder = NULL;
>  	return 0;
>  
> +stop_gc_thread:
> +	f2fs_stop_gc_thread(sbi);
>  sync_free_meta:
>  	/* safe to flush all the data */
>  	sync_filesystem(sbi->sb);
> -- 
> 2.49.0
> 
> 
> 
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