Date:   Wed, 8 Apr 2020 19:25:38 -0700
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Chao Yu <yuchao0@...wei.com>
Cc:     Sahitya Tummala <stummala@...eaurora.org>,
        linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH] f2fs: prevent meta updates while checkpoint
 is in progress

On 04/07, Chao Yu wrote:
> On 2020/4/7 10:58, Jaegeuk Kim wrote:
> > On 04/07, Chao Yu wrote:
> >> On 2020/4/4 1:27, Jaegeuk Kim wrote:
> >>> On 04/03, Jaegeuk Kim wrote:
> >>>> On 04/01, Sahitya Tummala wrote:
> >>>>> Hi Jaegeuk,
> >>>>>
> >>>>> Got it.
> >>>>> The diff below looks good to me.
> >>>>> Would you like me to test it and put a patch for this?
> >>>>
> >>>> Sahitya, Chao,
> >>>>
> >>>> Could you please take a look at this patch and test intensively?
> >>>>
> >>>> Thanks,
> >>>
> >>> v2:
> >>>
> >>> >From 6bf7d5b227d466b0fe90d4957af29bd184fb646e Mon Sep 17 00:00:00 2001
> >>> From: Jaegeuk Kim <jaegeuk@...nel.org>
> >>> Date: Tue, 31 Mar 2020 11:43:07 -0700
> >>> Subject: [PATCH] f2fs: refactor resize_fs to avoid meta updates in progress
> >>>
> >>> Sahitya raised an issue:
> >>> - prevent meta updates while checkpoint is in progress
> >>>
> >>> allocate_segment_for_resize() can cause metapage updates if
> >>> it requires to change the current node/data segments for resizing.
> >>> Stop these meta updates when there is a checkpoint already
> >>> in progress to prevent inconsistent CP data.
> >>>
> >>> Signed-off-by: Sahitya Tummala <stummala@...eaurora.org>
> >>> Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
> >>> ---
> >>>  fs/f2fs/checkpoint.c        |   6 +-
> >>>  fs/f2fs/f2fs.h              |   2 +-
> >>>  fs/f2fs/file.c              |   5 +-
> >>>  fs/f2fs/gc.c                | 107 +++++++++++++++++++-----------------
> >>>  fs/f2fs/super.c             |   1 -
> >>>  include/trace/events/f2fs.h |   4 +-
> >>>  6 files changed, 67 insertions(+), 58 deletions(-)
> >>>
> >>> diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
> >>> index 852890b72d6ac..531995192b714 100644
> >>> --- a/fs/f2fs/checkpoint.c
> >>> +++ b/fs/f2fs/checkpoint.c
> >>> @@ -1553,7 +1553,8 @@ int f2fs_write_checkpoint(struct f2fs_sb_info *sbi, struct cp_control *cpc)
> >>>  			return 0;
> >>>  		f2fs_warn(sbi, "Start checkpoint disabled!");
> >>>  	}
> >>> -	mutex_lock(&sbi->cp_mutex);
> >>> +	if (cpc->reason != CP_RESIZE)
> >>> +		mutex_lock(&sbi->cp_mutex);
> >>>  
> >>>  	if (!is_sbi_flag_set(sbi, SBI_IS_DIRTY) &&
> >>>  		((cpc->reason & CP_FASTBOOT) || (cpc->reason & CP_SYNC) ||
> >>> @@ -1622,7 +1623,8 @@ int f2fs_write_checkpoint(struct f2fs_sb_info *sbi, struct cp_control *cpc)
> >>>  	f2fs_update_time(sbi, CP_TIME);
> >>>  	trace_f2fs_write_checkpoint(sbi->sb, cpc->reason, "finish checkpoint");
> >>>  out:
> >>> -	mutex_unlock(&sbi->cp_mutex);
> >>> +	if (cpc->reason != CP_RESIZE)
> >>> +		mutex_unlock(&sbi->cp_mutex);
> >>>  	return err;
> >>>  }
> >>>  
> >>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> >>> index be02a5cadd944..f9b2caa2135bd 100644
> >>> --- a/fs/f2fs/f2fs.h
> >>> +++ b/fs/f2fs/f2fs.h
> >>> @@ -193,6 +193,7 @@ enum {
> >>>  #define	CP_DISCARD	0x00000010
> >>>  #define CP_TRIMMED	0x00000020
> >>>  #define CP_PAUSE	0x00000040
> >>> +#define CP_RESIZE 	0x00000080
> >>>  
> >>>  #define MAX_DISCARD_BLOCKS(sbi)		BLKS_PER_SEC(sbi)
> >>>  #define DEF_MAX_DISCARD_REQUEST		8	/* issue 8 discards per round */
> >>> @@ -1421,7 +1422,6 @@ struct f2fs_sb_info {
> >>>  	unsigned int segs_per_sec;		/* segments per section */
> >>>  	unsigned int secs_per_zone;		/* sections per zone */
> >>>  	unsigned int total_sections;		/* total section count */
> >>> -	struct mutex resize_mutex;		/* for resize exclusion */
> >>>  	unsigned int total_node_count;		/* total node block count */
> >>>  	unsigned int total_valid_node_count;	/* valid node block count */
> >>>  	loff_t max_file_blocks;			/* max block index of file */
> >>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> >>> index 257e61d0afffb..b4c12370bb3d6 100644
> >>> --- a/fs/f2fs/file.c
> >>> +++ b/fs/f2fs/file.c
> >>> @@ -3305,7 +3305,6 @@ static int f2fs_ioc_resize_fs(struct file *filp, unsigned long arg)
> >>>  {
> >>>  	struct f2fs_sb_info *sbi = F2FS_I_SB(file_inode(filp));
> >>>  	__u64 block_count;
> >>> -	int ret;
> >>>  
> >>>  	if (!capable(CAP_SYS_ADMIN))
> >>>  		return -EPERM;
> >>> @@ -3317,9 +3316,7 @@ static int f2fs_ioc_resize_fs(struct file *filp, unsigned long arg)
> >>>  			   sizeof(block_count)))
> >>>  		return -EFAULT;
> >>>  
> >>> -	ret = f2fs_resize_fs(sbi, block_count);
> >>> -
> >>> -	return ret;
> >>> +	return f2fs_resize_fs(sbi, block_count);
> >>>  }
> >>>  
> >>>  static int f2fs_ioc_enable_verity(struct file *filp, unsigned long arg)
> >>> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
> >>> index 26248c8936db0..46c75ecb64a2e 100644
> >>> --- a/fs/f2fs/gc.c
> >>> +++ b/fs/f2fs/gc.c
> >>> @@ -1399,12 +1399,29 @@ void f2fs_build_gc_manager(struct f2fs_sb_info *sbi)
> >>>  				GET_SEGNO(sbi, FDEV(0).end_blk) + 1;
> >>>  }
> >>>  
> >>> -static int free_segment_range(struct f2fs_sb_info *sbi, unsigned int start,
> >>> -							unsigned int end)
> >>> +static int free_segment_range(struct f2fs_sb_info *sbi,
> >>> +				unsigned int secs, bool gc_only)
> >>>  {
> >>> -	int type;
> >>> -	unsigned int segno, next_inuse;
> >>> +	unsigned int segno, next_inuse, start, end;
> >>> +	struct cp_control cpc = { CP_RESIZE, 0, 0, 0 };
> >>> +	int gc_mode, gc_type;
> >>>  	int err = 0;
> >>> +	int type;
> >>> +
> >>> +	/* Force block allocation for GC */
> >>> +	MAIN_SECS(sbi) -= secs;
> >>> +	start = MAIN_SECS(sbi) * sbi->segs_per_sec;
> >>> +	end = MAIN_SEGS(sbi) - 1;
> >>> +
> >>> +	mutex_lock(&DIRTY_I(sbi)->seglist_lock);
> >>> +	for (gc_mode = 0; gc_mode < MAX_GC_POLICY; gc_mode++)
> >>> +		if (SIT_I(sbi)->last_victim[gc_mode] >= start)
> >>> +			SIT_I(sbi)->last_victim[gc_mode] = 0;
> >>> +
> >>> +	for (gc_type = BG_GC; gc_type <= FG_GC; gc_type++)
> >>> +		if (sbi->next_victim_seg[gc_type] >= start)
> >>> +			sbi->next_victim_seg[gc_type] = NULL_SEGNO;
> >>> +	mutex_unlock(&DIRTY_I(sbi)->seglist_lock);
> >>>  
> >>>  	/* Move out cursegs from the target range */
> >>>  	for (type = CURSEG_HOT_DATA; type < NR_CURSEG_TYPE; type++)
> >>> @@ -1417,18 +1434,20 @@ static int free_segment_range(struct f2fs_sb_info *sbi, unsigned int start,
> >>>  			.iroot = RADIX_TREE_INIT(gc_list.iroot, GFP_NOFS),
> >>>  		};
> >>>  
> >>> -		down_write(&sbi->gc_lock);
> >>>  		do_garbage_collect(sbi, segno, &gc_list, FG_GC);
> >>> -		up_write(&sbi->gc_lock);
> >>>  		put_gc_inode(&gc_list);
> >>>  
> >>> -		if (get_valid_blocks(sbi, segno, true))
> >>> -			return -EAGAIN;
> >>> +		if (!gc_only && get_valid_blocks(sbi, segno, true)) {
> >>> +			err = -EAGAIN;
> >>> +			goto out;
> >>> +		}
> >>>  	}
> >>> +	if (gc_only)
> >>> +		goto out;
> >>>  
> >>> -	err = f2fs_sync_fs(sbi->sb, 1);
> >>> +	err = f2fs_write_checkpoint(sbi, &cpc);
> >>>  	if (err)
> >>> -		return err;
> >>> +		goto out;
> >>>  
> >>>  	next_inuse = find_next_inuse(FREE_I(sbi), end + 1, start);
> >>>  	if (next_inuse <= end) {
> >>> @@ -1436,6 +1455,8 @@ static int free_segment_range(struct f2fs_sb_info *sbi, unsigned int start,
> >>>  			 next_inuse);
> >>>  		f2fs_bug_on(sbi, 1);
> >>>  	}
> >>> +out:
> >>> +	MAIN_SECS(sbi) -= secs;
> >>>  	return err;
> >>>  }
> >>>  
> >>> @@ -1481,6 +1502,7 @@ static void update_fs_metadata(struct f2fs_sb_info *sbi, int secs)
> >>>  
> >>>  	SM_I(sbi)->segment_count = (int)SM_I(sbi)->segment_count + segs;
> >>>  	MAIN_SEGS(sbi) = (int)MAIN_SEGS(sbi) + segs;
> >>> +	MAIN_SECS(sbi) += secs;
> >>>  	FREE_I(sbi)->free_sections = (int)FREE_I(sbi)->free_sections + secs;
> >>>  	FREE_I(sbi)->free_segments = (int)FREE_I(sbi)->free_segments + segs;
> >>>  	F2FS_CKPT(sbi)->user_block_count = cpu_to_le64(user_block_count + blks);
> >>> @@ -1502,8 +1524,8 @@ static void update_fs_metadata(struct f2fs_sb_info *sbi, int secs)
> >>>  int f2fs_resize_fs(struct f2fs_sb_info *sbi, __u64 block_count)
> >>>  {
> >>>  	__u64 old_block_count, shrunk_blocks;
> >>> +	struct cp_control cpc = { CP_RESIZE, 0, 0, 0 };
> >>>  	unsigned int secs;
> >>> -	int gc_mode, gc_type;
> >>>  	int err = 0;
> >>>  	__u32 rem;
> >>>  
> >>> @@ -1538,10 +1560,22 @@ int f2fs_resize_fs(struct f2fs_sb_info *sbi, __u64 block_count)
> >>>  		return -EINVAL;
> >>>  	}
> >>>  
> >>> -	freeze_bdev(sbi->sb->s_bdev);
> >>> -
> >>>  	shrunk_blocks = old_block_count - block_count;
> >>>  	secs = div_u64(shrunk_blocks, BLKS_PER_SEC(sbi));
> >>> +
> >>> +	/* protect MAIN_SEC in free_segment_range */
> >>> +	f2fs_lock_op(sbi);
> >>> +	err = free_segment_range(sbi, secs, true);
> >>
> >> For this path, we break the rule that we need hold gc_lock during
> >> do_garbage_collect().
> > 
> > I don't get the point.
> > In free_segment_range(), gc_lock is held before/after do_garbage_collect().
> 
> @@ -1417,18 +1434,20 @@ static int free_segment_range(struct f2fs_sb_info *sbi, unsigned int start,
>  			.iroot = RADIX_TREE_INIT(gc_list.iroot, GFP_NOFS),
>  		};
> 
> -		down_write(&sbi->gc_lock);
>  		do_garbage_collect(sbi, segno, &gc_list, FG_GC);
> -		up_write(&sbi->gc_lock);
>  		put_gc_inode(&gc_list);
> 
> They were removed, right?

Ah, I messed up the patches. Yes, it seems I removed it.

> 
> > 
> >>
> >> One other concern is that still the granularity of lock_op is too large,
> >> to avoid potential hang if it triggers heavy gc migration, how about using
> >> a timeout mechanism in free_segment_range() like we did in
> >> f2fs_disable_checkpoint()?
> > 
> > We can do first round GC without f2fs_lock_op().
> 
> Yup, that makes sense to me.
> 
> > 
> >>
> >>> +	f2fs_unlock_op(sbi);
> >>> +	if (err)
> >>> +		return err;
> >>> +
> >>> +	set_sbi_flag(sbi, SBI_IS_RESIZEFS);
> >>> +
> >>> +	freeze_super(sbi->sb);
> >>> +	down_write(&sbi->gc_lock);
> >>> +	mutex_lock(&sbi->cp_mutex);
> >>> +
> >>>  	spin_lock(&sbi->stat_lock);
> >>>  	if (shrunk_blocks + valid_user_blocks(sbi) +
> >>>  		sbi->current_reserved_blocks + sbi->unusable_block_count +
> >>> @@ -1550,69 +1584,44 @@ int f2fs_resize_fs(struct f2fs_sb_info *sbi, __u64 block_count)
> >>>  	else
> >>>  		sbi->user_block_count -= shrunk_blocks;
> >>>  	spin_unlock(&sbi->stat_lock);
> >>> -	if (err) {
> >>> -		thaw_bdev(sbi->sb->s_bdev, sbi->sb);
> >>> -		return err;
> >>> -	}
> >>> -
> >>> -	mutex_lock(&sbi->resize_mutex);
> >>> -	set_sbi_flag(sbi, SBI_IS_RESIZEFS);
> >>> -
> >>> -	mutex_lock(&DIRTY_I(sbi)->seglist_lock);
> >>> -
> >>> -	MAIN_SECS(sbi) -= secs;
> >>> -
> >>> -	for (gc_mode = 0; gc_mode < MAX_GC_POLICY; gc_mode++)
> >>> -		if (SIT_I(sbi)->last_victim[gc_mode] >=
> >>> -					MAIN_SECS(sbi) * sbi->segs_per_sec)
> >>> -			SIT_I(sbi)->last_victim[gc_mode] = 0;
> >>> -
> >>> -	for (gc_type = BG_GC; gc_type <= FG_GC; gc_type++)
> >>> -		if (sbi->next_victim_seg[gc_type] >=
> >>> -					MAIN_SECS(sbi) * sbi->segs_per_sec)
> >>> -			sbi->next_victim_seg[gc_type] = NULL_SEGNO;
> >>> -
> >>> -	mutex_unlock(&DIRTY_I(sbi)->seglist_lock);
> >>> +	if (err)
> >>> +		goto out_err;
> >>>  
> >>> -	err = free_segment_range(sbi, MAIN_SECS(sbi) * sbi->segs_per_sec,
> >>> -			MAIN_SEGS(sbi) - 1);
> >>> +	err = free_segment_range(sbi, secs, false);
> >>
> >> Lock coverage is still large here, what about just checking the resize condition
> >> with find_next_inuse(, end + 1, start), if the migration finished, then let's call
> >> write_checkpoint(), otherwise, returning -EAGAIN.
> > 
> > We did GC above, so how much time do you expect to complete here? Basically
> 
> Just to consider handling corner case here, which is in between round 1 and round 2
> GC, there may occur a fair mount of data writes locating in the tail of device.
> 
> > I hesitate to return EAGAIN, since there's no context with respect to how
> > many times user need to retry to get succeess. Disabling checkpoint has
> 
> I think user can accept EAGAIN if we describe clearly about that the interface
> may fail due to concurrent IO on device, if the administrator want to resize
> successfully, concurrent operation on device should be avoided.
> 
> > some ways to get a sense tho. Nevertheless, if we want to return EAGAIN,
> > it'd be better to give # of bytes that it requires to migrate further?
> 
> Hmm.. I don't think there is such number, as resize should be atomic.

I thought we can return roughly # of dirty segments?

> 
> Thanks,
> 
> > 
> >>
> >>>  	if (err)
> >>> -		goto out;
> >>> +		goto recover_out;
> >>>  
> >>>  	update_sb_metadata(sbi, -secs);
> >>>  
> >>>  	err = f2fs_commit_super(sbi, false);
> >>>  	if (err) {
> >>>  		update_sb_metadata(sbi, secs);
> >>> -		goto out;
> >>> +		goto recover_out;
> >>>  	}
> >>>  
> >>> -	mutex_lock(&sbi->cp_mutex);
> >>>  	update_fs_metadata(sbi, -secs);
> >>>  	clear_sbi_flag(sbi, SBI_IS_RESIZEFS);
> >>>  	set_sbi_flag(sbi, SBI_IS_DIRTY);
> >>> -	mutex_unlock(&sbi->cp_mutex);
> >>>  
> >>> -	err = f2fs_sync_fs(sbi->sb, 1);
> >>> +	err = f2fs_write_checkpoint(sbi, &cpc);
> >>>  	if (err) {
> >>> -		mutex_lock(&sbi->cp_mutex);
> >>>  		update_fs_metadata(sbi, secs);
> >>> -		mutex_unlock(&sbi->cp_mutex);
> >>>  		update_sb_metadata(sbi, secs);
> >>>  		f2fs_commit_super(sbi, false);
> >>>  	}
> >>> -out:
> >>> +recover_out:
> >>>  	if (err) {
> >>>  		set_sbi_flag(sbi, SBI_NEED_FSCK);
> >>>  		f2fs_err(sbi, "resize_fs failed, should run fsck to repair!");
> >>>  
> >>> -		MAIN_SECS(sbi) += secs;
> >>>  		spin_lock(&sbi->stat_lock);
> >>>  		sbi->user_block_count += shrunk_blocks;
> >>>  		spin_unlock(&sbi->stat_lock);
> >>>  	}
> >>> +out_err:
> >>> +	mutex_unlock(&sbi->cp_mutex);
> >>> +	up_write(&sbi->gc_lock);
> >>> +	thaw_super(sbi->sb);
> >>>  	clear_sbi_flag(sbi, SBI_IS_RESIZEFS);
> >>> -	mutex_unlock(&sbi->resize_mutex);
> >>> -	thaw_bdev(sbi->sb->s_bdev, sbi->sb);
> >>>  	return err;
> >>>  }
> >>> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
> >>> index b83b17b54a0a6..1e7b1d21d0177 100644
> >>> --- a/fs/f2fs/super.c
> >>> +++ b/fs/f2fs/super.c
> >>> @@ -3412,7 +3412,6 @@ static int f2fs_fill_super(struct super_block *sb, void *data, int silent)
> >>>  	init_rwsem(&sbi->gc_lock);
> >>>  	mutex_init(&sbi->writepages);
> >>>  	mutex_init(&sbi->cp_mutex);
> >>> -	mutex_init(&sbi->resize_mutex);
> >>>  	init_rwsem(&sbi->node_write);
> >>>  	init_rwsem(&sbi->node_change);
> >>>  
> >>> diff --git a/include/trace/events/f2fs.h b/include/trace/events/f2fs.h
> >>> index 4d7d4c391879d..5d1a72001fdb4 100644
> >>> --- a/include/trace/events/f2fs.h
> >>> +++ b/include/trace/events/f2fs.h
> >>> @@ -50,6 +50,7 @@ TRACE_DEFINE_ENUM(CP_RECOVERY);
> >>>  TRACE_DEFINE_ENUM(CP_DISCARD);
> >>>  TRACE_DEFINE_ENUM(CP_TRIMMED);
> >>>  TRACE_DEFINE_ENUM(CP_PAUSE);
> >>> +TRACE_DEFINE_ENUM(CP_RESIZE);
> >>>  
> >>>  #define show_block_type(type)						\
> >>>  	__print_symbolic(type,						\
> >>> @@ -126,7 +127,8 @@ TRACE_DEFINE_ENUM(CP_PAUSE);
> >>>  		{ CP_RECOVERY,	"Recovery" },				\
> >>>  		{ CP_DISCARD,	"Discard" },				\
> >>>  		{ CP_PAUSE,	"Pause" },				\
> >>> -		{ CP_TRIMMED,	"Trimmed" })
> >>> +		{ CP_TRIMMED,	"Trimmed" },				\
> >>> +		{ CP_RESIZE,	"Resize" })
> >>>  
> >>>  #define show_fsync_cpreason(type)					\
> >>>  	__print_symbolic(type,						\
> >>>
> > .
> > 

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