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From: Jaegeuk Kim <jaegeuk@kernel.org>
To: Chao Yu <chao@kernel.org>
Cc: linux-kernel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH v2] f2fs: avoid fi->i_gc_rwsem[WRITE] lock in f2fs_gc
Date: Sun, 5 Aug 2018 09:08:42 -0700
Message-ID: <20180805160842.GA55836@jaegeuk-macbookpro.roam.corp.google.com> (raw)
In-Reply-To: <4ab08c78-4a3a-4161-9c6f-2835829c95c3@kernel.org>

On 08/05, Chao Yu wrote:
> On 2018/8/5 6:29, Jaegeuk Kim wrote:
> > The f2fs_gc() called by f2fs_balance_fs() requires to be called outside of
> > fi->i_gc_rwsem[WRITE], since f2fs_gc() can try to grab it in a loop.
> > 
> > If it hits the miximum retrials in GC, let's give a chance to release
> > gc_mutex for a short time in order not to go into live lock in the worst
> > case.
> > 
> > Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
> > ---
> > v2 log from v1:
> >  - keep lock order: i_gc_rwsem -> lock_op
> > 
> >  fs/f2fs/f2fs.h    |  1 +
> >  fs/f2fs/file.c    | 76 ++++++++++++++++++++++++-----------------------
> >  fs/f2fs/gc.c      | 22 ++++++++++----
> >  fs/f2fs/segment.c |  5 +++-
> >  fs/f2fs/segment.h |  2 +-
> >  5 files changed, 61 insertions(+), 45 deletions(-)
> > 
> > diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> > index a9447c7d6570..50349780001b 100644
> > --- a/fs/f2fs/f2fs.h
> > +++ b/fs/f2fs/f2fs.h
> > @@ -1223,6 +1223,7 @@ struct f2fs_sb_info {
> >  	unsigned int gc_mode;			/* current GC state */
> >  	/* for skip statistic */
> >  	unsigned long long skipped_atomic_files[2];	/* FG_GC and BG_GC */
> > +	unsigned long long skipped_gc_rwsem;		/* FG_GC only */
> >  
> >  	/* threshold for gc trials on pinned files */
> >  	u64 gc_pin_file_threshold;
> > diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> > index 78c1bd6b8497..7bcf47f41ef1 100644
> > --- a/fs/f2fs/file.c
> > +++ b/fs/f2fs/file.c
> > @@ -1179,25 +1179,31 @@ static int __exchange_data_block(struct inode *src_inode,
> >  	return ret;
> >  }
> >  
> > -static int f2fs_do_collapse(struct inode *inode, pgoff_t start, pgoff_t end)
> > +static int f2fs_do_collapse(struct inode *inode, loff_t offset, loff_t len)
> >  {
> >  	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
> >  	pgoff_t nrpages = (i_size_read(inode) + PAGE_SIZE - 1) / PAGE_SIZE;
> > +	pgoff_t start = offset >> PAGE_SHIFT;
> > +	pgoff_t end = (offset + len) >> PAGE_SHIFT;
> >  	int ret;
> >  
> >  	f2fs_balance_fs(sbi, true);
> > -	f2fs_lock_op(sbi);
> >  
> > -	f2fs_drop_extent_tree(inode);
> > +	/* avoid gc operation during block exchange */
> > +	down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> >  
> > +	f2fs_lock_op(sbi);
> > +	f2fs_drop_extent_tree(inode);
> > +	truncate_pagecache(inode, offset);
> >  	ret = __exchange_data_block(inode, inode, end, start, nrpages - end, true);
> >  	f2fs_unlock_op(sbi);
> > +
> > +	up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> >  	return ret;
> >  }
> >  
> >  static int f2fs_collapse_range(struct inode *inode, loff_t offset, loff_t len)
> >  {
> > -	pgoff_t pg_start, pg_end;
> >  	loff_t new_size;
> >  	int ret;
> >  
> > @@ -1212,21 +1218,13 @@ static int f2fs_collapse_range(struct inode *inode, loff_t offset, loff_t len)
> >  	if (ret)
> >  		return ret;
> >  
> > -	pg_start = offset >> PAGE_SHIFT;
> > -	pg_end = (offset + len) >> PAGE_SHIFT;
> > -
> > -	/* avoid gc operation during block exchange */
> > -	down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> > -
> >  	down_write(&F2FS_I(inode)->i_mmap_sem);
> >  	/* write out all dirty pages from offset */
> >  	ret = filemap_write_and_wait_range(inode->i_mapping, offset, LLONG_MAX);
> >  	if (ret)
> >  		goto out_unlock;
> >  
> > -	truncate_pagecache(inode, offset);
> > -
> > -	ret = f2fs_do_collapse(inode, pg_start, pg_end);
> > +	ret = f2fs_do_collapse(inode, offset, len);
> >  	if (ret)
> >  		goto out_unlock;
> >  
> > @@ -1242,7 +1240,6 @@ static int f2fs_collapse_range(struct inode *inode, loff_t offset, loff_t len)
> >  		f2fs_i_size_write(inode, new_size);
> >  out_unlock:
> >  	up_write(&F2FS_I(inode)->i_mmap_sem);
> > -	up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> >  	return ret;
> >  }
> >  
> > @@ -1417,9 +1414,6 @@ static int f2fs_insert_range(struct inode *inode, loff_t offset, loff_t len)
> >  
> >  	f2fs_balance_fs(sbi, true);
> >  
> > -	/* avoid gc operation during block exchange */
> > -	down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> > -
> >  	down_write(&F2FS_I(inode)->i_mmap_sem);
> >  	ret = f2fs_truncate_blocks(inode, i_size_read(inode), true);
> >  	if (ret)
> > @@ -1430,13 +1424,15 @@ static int f2fs_insert_range(struct inode *inode, loff_t offset, loff_t len)
> >  	if (ret)
> >  		goto out;
> >  
> > -	truncate_pagecache(inode, offset);
> > -
> >  	pg_start = offset >> PAGE_SHIFT;
> >  	pg_end = (offset + len) >> PAGE_SHIFT;
> >  	delta = pg_end - pg_start;
> >  	idx = (i_size_read(inode) + PAGE_SIZE - 1) / PAGE_SIZE;
> >  
> > +	/* avoid gc operation during block exchange */
> > +	down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> > +	truncate_pagecache(inode, offset);
> > +
> >  	while (!ret && idx > pg_start) {
> >  		nr = idx - pg_start;
> >  		if (nr > delta)
> > @@ -1450,6 +1446,7 @@ static int f2fs_insert_range(struct inode *inode, loff_t offset, loff_t len)
> >  					idx + delta, nr, false);
> >  		f2fs_unlock_op(sbi);
> >  	}
> > +	up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> >  
> >  	/* write out all moved pages, if possible */
> >  	filemap_write_and_wait_range(inode->i_mapping, offset, LLONG_MAX);
> > @@ -1459,7 +1456,6 @@ static int f2fs_insert_range(struct inode *inode, loff_t offset, loff_t len)
> >  		f2fs_i_size_write(inode, new_size);
> >  out:
> >  	up_write(&F2FS_I(inode)->i_mmap_sem);
> > -	up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> >  	return ret;
> >  }
> >  
> > @@ -1706,8 +1702,6 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)
> >  
> >  	inode_lock(inode);
> >  
> > -	down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> > -
> >  	if (f2fs_is_atomic_file(inode)) {
> >  		if (is_inode_flag_set(inode, FI_ATOMIC_REVOKE_REQUEST))
> >  			ret = -EINVAL;
> > @@ -1718,6 +1712,8 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)
> >  	if (ret)
> >  		goto out;
> >  
> > +	down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> > +
> >  	if (!get_dirty_pages(inode))
> >  		goto skip_flush;
> >  
> > @@ -1725,18 +1721,20 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)
> >  		"Unexpected flush for atomic writes: ino=%lu, npages=%u",
> >  					inode->i_ino, get_dirty_pages(inode));
> >  	ret = filemap_write_and_wait_range(inode->i_mapping, 0, LLONG_MAX);
> > -	if (ret)
> > +	if (ret) {
> > +		up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> >  		goto out;
> > +	}
> >  skip_flush:
> >  	set_inode_flag(inode, FI_ATOMIC_FILE);
> >  	clear_inode_flag(inode, FI_ATOMIC_REVOKE_REQUEST);
> > -	f2fs_update_time(F2FS_I_SB(inode), REQ_TIME);
> > +	up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> >  
> > +	f2fs_update_time(F2FS_I_SB(inode), REQ_TIME);
> >  	F2FS_I(inode)->inmem_task = current;
> >  	stat_inc_atomic_write(inode);
> >  	stat_update_max_atomic_write(inode);
> >  out:
> > -	up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> >  	inode_unlock(inode);
> >  	mnt_drop_write_file(filp);
> >  	return ret;
> > @@ -1754,9 +1752,9 @@ static int f2fs_ioc_commit_atomic_write(struct file *filp)
> >  	if (ret)
> >  		return ret;
> >  
> > -	inode_lock(inode);
> > +	f2fs_balance_fs(F2FS_I_SB(inode), true);
> >  
> > -	down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> > +	inode_lock(inode);
> >  
> >  	if (f2fs_is_volatile_file(inode)) {
> >  		ret = -EINVAL;
> > @@ -1782,7 +1780,6 @@ static int f2fs_ioc_commit_atomic_write(struct file *filp)
> >  		clear_inode_flag(inode, FI_ATOMIC_REVOKE_REQUEST);
> >  		ret = -EINVAL;
> >  	}
> > -	up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> >  	inode_unlock(inode);
> >  	mnt_drop_write_file(filp);
> >  	return ret;
> > @@ -2378,15 +2375,10 @@ static int f2fs_move_file_range(struct file *file_in, loff_t pos_in,
> >  	}
> >  
> >  	inode_lock(src);
> > -	down_write(&F2FS_I(src)->i_gc_rwsem[WRITE]);
> >  	if (src != dst) {
> >  		ret = -EBUSY;
> >  		if (!inode_trylock(dst))
> >  			goto out;
> > -		if (!down_write_trylock(&F2FS_I(dst)->i_gc_rwsem[WRITE])) {
> > -			inode_unlock(dst);
> > -			goto out;
> > -		}
> >  	}
> >  
> >  	ret = -EINVAL;
> > @@ -2431,6 +2423,14 @@ static int f2fs_move_file_range(struct file *file_in, loff_t pos_in,
> >  		goto out_unlock;
> >  
> >  	f2fs_balance_fs(sbi, true);
> > +
> > +	down_write(&F2FS_I(src)->i_gc_rwsem[WRITE]);
> > +	if (src != dst) {
> > +		ret = -EBUSY;
> > +		if (!down_write_trylock(&F2FS_I(dst)->i_gc_rwsem[WRITE]))
> > +			goto out_src;
> > +	}
> > +
> >  	f2fs_lock_op(sbi);
> >  	ret = __exchange_data_block(src, dst, pos_in >> F2FS_BLKSIZE_BITS,
> >  				pos_out >> F2FS_BLKSIZE_BITS,
> > @@ -2443,13 +2443,15 @@ static int f2fs_move_file_range(struct file *file_in, loff_t pos_in,
> >  			f2fs_i_size_write(dst, dst_osize);
> >  	}
> >  	f2fs_unlock_op(sbi);
> > -out_unlock:
> > -	if (src != dst) {
> > +
> > +	if (src != dst)
> >  		up_write(&F2FS_I(dst)->i_gc_rwsem[WRITE]);
> > +out_src:
> > +	up_write(&F2FS_I(src)->i_gc_rwsem[WRITE]);
> > +out_unlock:
> > +	if (src != dst)
> >  		inode_unlock(dst);
> > -	}
> >  out:
> > -	up_write(&F2FS_I(src)->i_gc_rwsem[WRITE]);
> >  	inode_unlock(src);
> >  	return ret;
> >  }
> > diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
> > index e352fbd33848..cac317e37306 100644
> > --- a/fs/f2fs/gc.c
> > +++ b/fs/f2fs/gc.c
> > @@ -884,6 +884,7 @@ static void gc_data_segment(struct f2fs_sb_info *sbi, struct f2fs_summary *sum,
> >  			if (!down_write_trylock(
> >  				&F2FS_I(inode)->i_gc_rwsem[WRITE])) {
> >  				iput(inode);
> > +				sbi->skipped_gc_rwsem++;
> >  				continue;
> >  			}
> >  
> > @@ -913,6 +914,7 @@ static void gc_data_segment(struct f2fs_sb_info *sbi, struct f2fs_summary *sum,
> >  					continue;
> >  				if (!down_write_trylock(
> >  						&fi->i_gc_rwsem[WRITE])) {
> > +					sbi->skipped_gc_rwsem++;
> >  					up_write(&fi->i_gc_rwsem[READ]);
> >  					continue;
> >  				}
> > @@ -1062,6 +1064,7 @@ int f2fs_gc(struct f2fs_sb_info *sbi, bool sync,
> >  				prefree_segments(sbi));
> >  
> >  	cpc.reason = __get_cp_reason(sbi);
> > +	sbi->skipped_gc_rwsem = 0;
> >  gc_more:
> >  	if (unlikely(!(sbi->sb->s_flags & SB_ACTIVE))) {
> >  		ret = -EINVAL;
> > @@ -1103,7 +1106,8 @@ int f2fs_gc(struct f2fs_sb_info *sbi, bool sync,
> >  	total_freed += seg_freed;
> >  
> >  	if (gc_type == FG_GC) {
> > -		if (sbi->skipped_atomic_files[FG_GC] > last_skipped)
> > +		if (sbi->skipped_atomic_files[FG_GC] > last_skipped ||
> > +						sbi->skipped_gc_rwsem)
> 
> There should be other foreground ops like DIO can race with GC, in such case, if
> we increase sbi->skipped_gc_rwsem, and call f2fs_drop_inmem_pages_all() to drop
> inmem pages later, it doesn't help?

Let me add a condition to decide that.

> 
> >  			skipped_round++;
> >  		last_skipped = sbi->skipped_atomic_files[FG_GC];
> >  		round++;
> > @@ -1112,15 +1116,21 @@ int f2fs_gc(struct f2fs_sb_info *sbi, bool sync,
> >  	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)
> > -				f2fs_drop_inmem_pages_all(sbi, true);
> > +	if (sync)
> > +		goto stop;
> > +
> > +	if (has_not_enough_free_secs(sbi, sec_freed, 0)) {
> > +		if (skipped_round <= MAX_SKIP_GC_COUNT ||
> > +					skipped_round * 2 < round) {
> >  			segno = NULL_SEGNO;
> >  			goto gc_more;
> >  		}
> >  
> > +		if (sbi->skipped_atomic_files[FG_GC] == last_skipped) {
> > +			f2fs_drop_inmem_pages_all(sbi, true);
> > +			segno = NULL_SEGNO;
> > +			goto gc_more;
> > +		}
> >  		if (gc_type == FG_GC)
> >  			ret = f2fs_write_checkpoint(sbi, &cpc);
> >  	}
> > diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> > index 3662e1f429b4..15b3b095fd58 100644
> > --- a/fs/f2fs/segment.c
> > +++ b/fs/f2fs/segment.c
> > @@ -444,10 +444,12 @@ int f2fs_commit_inmem_pages(struct inode *inode)
> >  	struct f2fs_inode_info *fi = F2FS_I(inode);
> >  	int err;
> >  
> > -	f2fs_balance_fs(sbi, true);
> > +	f2fs_balance_fs(F2FS_I_SB(inode), true);
> 
> We don't need to change sbi to F2FS_I_SB(inode).
> 
> down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);

Done.

> 
> Thanks,
> 
> > +
> >  	f2fs_lock_op(sbi);
> >  
> >  	set_inode_flag(inode, FI_ATOMIC_COMMIT);
> > +	down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> >  
> >  	mutex_lock(&fi->inmem_lock);
> >  	err = __f2fs_commit_inmem_pages(inode);
> > @@ -458,6 +460,7 @@ int f2fs_commit_inmem_pages(struct inode *inode)
> >  	spin_unlock(&sbi->inode_lock[ATOMIC_FILE]);
> >  	mutex_unlock(&fi->inmem_lock);
> >  
> > +	up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> >  	clear_inode_flag(inode, FI_ATOMIC_COMMIT);
> >  
> >  	f2fs_unlock_op(sbi);
> > diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
> > index 50495515f0a0..b3d9e317ff0c 100644
> > --- a/fs/f2fs/segment.h
> > +++ b/fs/f2fs/segment.h
> > @@ -215,7 +215,7 @@ struct segment_allocation {
> >  #define IS_DUMMY_WRITTEN_PAGE(page)			\
> >  		(page_private(page) == (unsigned long)DUMMY_WRITTEN_PAGE)
> >  
> > -#define MAX_SKIP_ATOMIC_COUNT			16
> > +#define MAX_SKIP_GC_COUNT			16
> >  
> >  struct inmem_pages {
> >  	struct list_head list;
> > 

  reply index

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-07-30  1:32 [PATCH] " Jaegeuk Kim
2018-07-30  3:29 ` Chao Yu
2018-07-30  4:18   ` Jaegeuk Kim
2018-07-30  6:36     ` Chao Yu
2018-07-30  9:08       ` Jaegeuk Kim
2018-07-30  9:28         ` Chao Yu
2018-07-30 10:00           ` Jaegeuk Kim
2018-08-04  2:31             ` [f2fs-dev] " Chao Yu
2018-08-12 10:24               ` Chao Yu
2018-08-13 20:12                 ` Jaegeuk Kim
2018-08-14  6:21                   ` Chao Yu
2018-08-04 22:29 ` [PATCH v2] " Jaegeuk Kim
2018-08-05 14:42   ` [f2fs-dev] " Chao Yu
2018-08-05 16:08     ` Jaegeuk Kim [this message]
2018-08-05 16:34   ` [f2fs-dev] [PATCH v3] " Jaegeuk Kim
2018-08-09  1:44     ` Chao Yu
2018-08-09 19:59       ` Jaegeuk Kim
2018-08-10  1:36         ` Chao Yu
2018-08-10  1:46           ` Jaegeuk Kim
2018-08-20  7:13             ` Chao Yu

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