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Date:   Fri, 27 Apr 2018 09:51:36 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     Jaegeuk Kim <jaegeuk@...nel.org>
CC:     <linux-f2fs-devel@...ts.sourceforge.net>,
        <linux-kernel@...r.kernel.org>, <chao@...nel.org>
Subject: Re: [PATCH v2] f2fs: avoid stucking GC due to atomic write

On 2018/4/26 23:54, Jaegeuk Kim wrote:
> On 04/24, Chao Yu wrote:
>> f2fs doesn't allow abuse on atomic write class interface, so except
>> limiting in-mem pages' total memory usage capacity, we need to limit
>> atomic-write usage as well when filesystem is seriously fragmented,
>> otherwise we may run into infinite loop during foreground GC because
>> target blocks in victim segment are belong to atomic opened file for
>> long time.
> 
> How about using fi->i_gc_failure likewise pin_file?

OK, how about changing it to array fi->i_gc_failure[MAX_GC_FAILURE], and change
the type to unsigned long long to avoid overflow?

enum {
	GC_FAILURE_PIN,
	GC_FAILURE_ATOMIC,
	MAX_GC_FAILURE
}

Thanks,

> 
>>
>> Now, we will detect failure due to atomic write in foreground GC, if
>> the count exceeds threshold, we will drop all atomic written data in
>> cache, by this, I expect it can keep our system running safely to
>> prevent Dos attack.
>>
>> In addition, his patch adds to show GC skip information in debugfs,
>> now it just shows count of skipped caused by atomic write.
>>
>> Signed-off-by: Chao Yu <yuchao0@...wei.com>
>> ---
>> v2:
>> - add to show skip info in debugfs.
>>  fs/f2fs/debug.c   |  8 ++++++++
>>  fs/f2fs/f2fs.h    |  2 ++
>>  fs/f2fs/file.c    |  5 +++++
>>  fs/f2fs/gc.c      | 29 +++++++++++++++++++++++++----
>>  fs/f2fs/gc.h      |  3 +++
>>  fs/f2fs/segment.c |  1 +
>>  fs/f2fs/segment.h |  2 ++
>>  7 files changed, 46 insertions(+), 4 deletions(-)
>>
>> diff --git a/fs/f2fs/debug.c b/fs/f2fs/debug.c
>> index 0fbd674c66fb..607b258a9b61 100644
>> --- a/fs/f2fs/debug.c
>> +++ b/fs/f2fs/debug.c
>> @@ -104,6 +104,10 @@ static void update_general_status(struct f2fs_sb_info *sbi)
>>  	si->avail_nids = NM_I(sbi)->available_nids;
>>  	si->alloc_nids = NM_I(sbi)->nid_cnt[PREALLOC_NID];
>>  	si->bg_gc = sbi->bg_gc;
>> +	si->skipped_atomic_files[BG_GC] =
>> +			sbi->gc_thread->skipped_atomic_files[BG_GC];
>> +	si->skipped_atomic_files[FG_GC] =
>> +			sbi->gc_thread->skipped_atomic_files[FG_GC];
>>  	si->util_free = (int)(free_user_blocks(sbi) >> sbi->log_blocks_per_seg)
>>  		* 100 / (int)(sbi->user_block_count >> sbi->log_blocks_per_seg)
>>  		/ 2;
>> @@ -341,6 +345,10 @@ static int stat_show(struct seq_file *s, void *v)
>>  				si->bg_data_blks);
>>  		seq_printf(s, "  - node blocks : %d (%d)\n", si->node_blks,
>>  				si->bg_node_blks);
>> +		seq_printf(s, "Skipped : atomic write %llu (%llu)\n",
>> +				si->skipped_atomic_files[BG_GC] +
>> +				si->skipped_atomic_files[FG_GC],
>> +				si->skipped_atomic_files[BG_GC]);
>>  		seq_puts(s, "\nExtent Cache:\n");
>>  		seq_printf(s, "  - Hit Count: L1-1:%llu L1-2:%llu L2:%llu\n",
>>  				si->hit_largest, si->hit_cached,
>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>> index 75d3b4875429..c2b92cb377c6 100644
>> --- a/fs/f2fs/f2fs.h
>> +++ b/fs/f2fs/f2fs.h
>> @@ -2254,6 +2254,7 @@ enum {
>>  	FI_EXTRA_ATTR,		/* indicate file has extra attribute */
>>  	FI_PROJ_INHERIT,	/* indicate file inherits projectid */
>>  	FI_PIN_FILE,		/* indicate file should not be gced */
>> +	FI_ATOMIC_REVOKE_REQUEST,/* indicate atomic committed data has been dropped */
>>  };
>>  
>>  static inline void __mark_inode_dirty_flag(struct inode *inode,
>> @@ -3010,6 +3011,7 @@ struct f2fs_stat_info {
>>  	int bg_node_segs, bg_data_segs;
>>  	int tot_blks, data_blks, node_blks;
>>  	int bg_data_blks, bg_node_blks;
>> +	unsigned long long skipped_atomic_files[2];
>>  	int curseg[NR_CURSEG_TYPE];
>>  	int cursec[NR_CURSEG_TYPE];
>>  	int curzone[NR_CURSEG_TYPE];
>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
>> index a352804af244..0cfa65c21d3f 100644
>> --- a/fs/f2fs/file.c
>> +++ b/fs/f2fs/file.c
>> @@ -1702,6 +1702,7 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)
>>  skip_flush:
>>  	set_inode_flag(inode, FI_HOT_DATA);
>>  	set_inode_flag(inode, FI_ATOMIC_FILE);
>> +	clear_inode_flag(inode, FI_ATOMIC_REVOKE_REQUEST);
>>  	f2fs_update_time(F2FS_I_SB(inode), REQ_TIME);
>>  
>>  	F2FS_I(inode)->inmem_task = current;
>> @@ -1750,6 +1751,10 @@ static int f2fs_ioc_commit_atomic_write(struct file *filp)
>>  		ret = f2fs_do_sync_file(filp, 0, LLONG_MAX, 1, false);
>>  	}
>>  err_out:
>> +	if (is_inode_flag_set(inode, FI_ATOMIC_REVOKE_REQUEST)) {
>> +		clear_inode_flag(inode, FI_ATOMIC_REVOKE_REQUEST);
>> +		ret = -EINVAL;
>> +	}
>>  	up_write(&F2FS_I(inode)->dio_rwsem[WRITE]);
>>  	inode_unlock(inode);
>>  	mnt_drop_write_file(filp);
>> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
>> index 2febb84b2fd6..ec6cb7b417a1 100644
>> --- a/fs/f2fs/gc.c
>> +++ b/fs/f2fs/gc.c
>> @@ -135,6 +135,9 @@ int init_gc_context(struct f2fs_sb_info *sbi)
>>  
>>  	init_rwsem(&gc_th->gc_rwsem);
>>  
>> +	gc_th->skipped_atomic_files[BG_GC] = 0;
>> +	gc_th->skipped_atomic_files[FG_GC] = 0;
>> +
>>  	sbi->gc_thread = gc_th;
>>  
>>  	return 0;
>> @@ -629,7 +632,7 @@ static bool is_alive(struct f2fs_sb_info *sbi, struct f2fs_summary *sum,
>>   * This can be used to move blocks, aka LBAs, directly on disk.
>>   */
>>  static void move_data_block(struct inode *inode, block_t bidx,
>> -					unsigned int segno, int off)
>> +				int gc_type, unsigned int segno, int off)
>>  {
>>  	struct f2fs_io_info fio = {
>>  		.sbi = F2FS_I_SB(inode),
>> @@ -656,8 +659,10 @@ static void move_data_block(struct inode *inode, block_t bidx,
>>  	if (!check_valid_map(F2FS_I_SB(inode), segno, off))
>>  		goto out;
>>  
>> -	if (f2fs_is_atomic_file(inode))
>> +	if (f2fs_is_atomic_file(inode)) {
>> +		GC_I(F2FS_I_SB(inode))->skipped_atomic_files[gc_type]++;
>>  		goto out;
>> +	}
>>  
>>  	if (f2fs_is_pinned_file(inode)) {
>>  		f2fs_pin_file_control(inode, true);
>> @@ -763,8 +768,10 @@ static void move_data_page(struct inode *inode, block_t bidx, int gc_type,
>>  	if (!check_valid_map(F2FS_I_SB(inode), segno, off))
>>  		goto out;
>>  
>> -	if (f2fs_is_atomic_file(inode))
>> +	if (f2fs_is_atomic_file(inode)) {
>> +		GC_I(F2FS_I_SB(inode))->skipped_atomic_files[gc_type]++;
>>  		goto out;
>> +	}
>>  	if (f2fs_is_pinned_file(inode)) {
>>  		if (gc_type == FG_GC)
>>  			f2fs_pin_file_control(inode, true);
>> @@ -926,7 +933,8 @@ static void gc_data_segment(struct f2fs_sb_info *sbi, struct f2fs_summary *sum,
>>  			start_bidx = start_bidx_of_node(nofs, inode)
>>  								+ ofs_in_node;
>>  			if (f2fs_post_read_required(inode))
>> -				move_data_block(inode, start_bidx, segno, off);
>> +				move_data_block(inode, start_bidx, gc_type,
>> +								segno, off);
>>  			else
>>  				move_data_page(inode, start_bidx, gc_type,
>>  								segno, off);
>> @@ -1043,6 +1051,9 @@ int f2fs_gc(struct f2fs_sb_info *sbi, bool sync,
>>  		.ilist = LIST_HEAD_INIT(gc_list.ilist),
>>  		.iroot = RADIX_TREE_INIT(gc_list.iroot, GFP_NOFS),
>>  	};
>> +	unsigned long long last_skipped =
>> +			GC_I(sbi)->skipped_atomic_files[FG_GC];
>> +	unsigned int skipped_round = 0, round = 0;
>>  
>>  	trace_f2fs_gc_begin(sbi->sb, sync, background,
>>  				get_pages(sbi, F2FS_DIRTY_NODES),
>> @@ -1094,11 +1105,21 @@ int f2fs_gc(struct f2fs_sb_info *sbi, bool sync,
>>  		sec_freed++;
>>  	total_freed += seg_freed;
>>  
>> +	if (gc_type == FG_GC) {
>> +		if (GC_I(sbi)->skipped_atomic_files[FG_GC] > last_skipped)
>> +			skipped_round++;
>> +		last_skipped = GC_I(sbi)->skipped_atomic_files[FG_GC];
>> +		round++;
>> +	}
>> +
>>  	if (gc_type == FG_GC)
>>  		sbi->cur_victim_sec = NULL_SEGNO;
>>  
>>  	if (!sync) {
>>  		if (has_not_enough_free_secs(sbi, sec_freed, 0)) {
>> +			if (skipped_round > MAX_SKIP_ATOMIC_COUNT &&
>> +				skipped_round * 2 >= round)
>> +				drop_inmem_pages_all(sbi);
>>  			segno = NULL_SEGNO;
>>  			goto gc_more;
>>  		}
>> diff --git a/fs/f2fs/gc.h b/fs/f2fs/gc.h
>> index 9a5b273328c2..9aa341cc4347 100644
>> --- a/fs/f2fs/gc.h
>> +++ b/fs/f2fs/gc.h
>> @@ -40,6 +40,9 @@ struct f2fs_gc_kthread {
>>  	unsigned int gc_idle;
>>  	unsigned int gc_urgent;
>>  	unsigned int gc_wake;
>> +
>> +	/* for skip statistic */
>> +	unsigned long long skipped_atomic_files[2];
>>  };
>>  
>>  struct gc_inode_list {
>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
>> index f787eea1b2f6..ce108a909d66 100644
>> --- a/fs/f2fs/segment.c
>> +++ b/fs/f2fs/segment.c
>> @@ -293,6 +293,7 @@ void drop_inmem_pages_all(struct f2fs_sb_info *sbi)
>>  	spin_unlock(&sbi->inode_lock[ATOMIC_FILE]);
>>  
>>  	if (inode) {
>> +		set_inode_flag(inode, FI_ATOMIC_REVOKE_REQUEST);
>>  		drop_inmem_pages(inode);
>>  		iput(inode);
>>  	}
>> diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
>> index 492ad0c86fa9..7702b054689c 100644
>> --- a/fs/f2fs/segment.h
>> +++ b/fs/f2fs/segment.h
>> @@ -215,6 +215,8 @@ struct segment_allocation {
>>  #define IS_DUMMY_WRITTEN_PAGE(page)			\
>>  		(page_private(page) == (unsigned long)DUMMY_WRITTEN_PAGE)
>>  
>> +#define MAX_SKIP_ATOMIC_COUNT			16
>> +
>>  struct inmem_pages {
>>  	struct list_head list;
>>  	struct page *page;
>> -- 
>> 2.15.0.55.gc2ece9dc4de6
> 
> .
> 

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