Re: [PATCH v2] f2fs: avoid stucking GC due to atomic write

[Jaegeuk Kim]

On 04/27, Chao Yu wrote:
> 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?

It'd be enough to share i_gc_failure between the types, IMO.

> 
> 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@xxxxxxxxxx>
> >> ---
> >> 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
> > 
> > .
> >