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From: Chao Yu <yuchao0@huawei.com>
To: Jaegeuk Kim <jaegeuk@kernel.org>
Cc: <linux-kernel@vger.kernel.org>, <linux-f2fs-devel@lists.sourceforge.net>
Subject: Re: [PATCH] f2fs: avoid fi->i_gc_rwsem[WRITE] lock in f2fs_gc
Date: Mon, 30 Jul 2018 17:28:12 +0800
Message-ID: <171084b5-acd5-97fa-205e-202b752baaf0@huawei.com> (raw)
In-Reply-To: <20180730090849.GA22089@jaegeuk-macbookpro.roam.corp.google.com>

On 2018/7/30 17:08, Jaegeuk Kim wrote:
> On 07/30, Chao Yu wrote:
>> On 2018/7/30 12:18, Jaegeuk Kim wrote:
>>> On 07/30, Chao Yu wrote:
>>>> On 2018/7/30 9:32, 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>
>>>>> ---
>>>>>  fs/f2fs/f2fs.h    |  1 +
>>>>>  fs/f2fs/file.c    | 62 ++++++++++++++++++++++-------------------------
>>>>>  fs/f2fs/gc.c      | 22 ++++++++++++-----
>>>>>  fs/f2fs/segment.c |  5 +++-
>>>>>  fs/f2fs/segment.h |  2 +-
>>>>>  5 files changed, 51 insertions(+), 41 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..2b7d26ebb294 100644
>>>>> --- a/fs/f2fs/file.c
>>>>> +++ b/fs/f2fs/file.c
>>>>> @@ -1179,10 +1179,12 @@ 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);
>>>>> @@ -1190,14 +1192,18 @@ static int f2fs_do_collapse(struct inode *inode, pgoff_t start, pgoff_t end)
>>>>>  
>>>>>  	f2fs_drop_extent_tree(inode);
>>>>>  
>>>>> +	/* avoid gc operation during block exchange */
>>>>> +	down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
>>>>> +	truncate_pagecache(inode, offset);
>>>>>  	ret = __exchange_data_block(inode, inode, end, start, nrpages - end, true);
>>>>> +	up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
>>>>> +
>>>>>  	f2fs_unlock_op(sbi);
>>>>>  	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]);
>>>>
>>>> After removing lock here, how can we handle below condition:
>>>>
>>>> commit 27319ba4044c0c67d62ae39e53c0118c89f0a029
>>>> Author: Chao Yu <yuchao0@huawei.com>
>>>> Date:   Tue Apr 17 17:51:28 2018 +0800
>>>>
>>>>     f2fs: fix race in between GC and atomic open
>>>>
>>>>     Thread                                  GC thread
>>>>     - f2fs_ioc_start_atomic_write
>>>>      - get_dirty_pages
>>>>      - filemap_write_and_wait_range
>>>>                                             - f2fs_gc
>>>>                                              - do_garbage_collect
>>>>                                               - gc_data_segment
>>>>                                                - move_data_page
>>>>                                                 - f2fs_is_atomic_file
>>>>                                                 - set_page_dirty
>>>>      - set_inode_flag(, FI_ATOMIC_FILE)
>>>>
>>>>     Dirty data page can still be generated by GC in race condition as
>>>>     above call stack.
>>>>
>>>>     This patch adds fi->dio_rwsem[WRITE] in f2fs_ioc_start_atomic_write
>>>>     to avoid such race.
>>>
>>> "f2fs: don't allow any writes on aborted atomic writes" disallows any writes
>>> on atomic file which has the revoking flag. So, this won't happen. In GC,
>>
>> Hmmm... In above condition, it's not related to FI_ATOMIC_REVOKE_REQUEST flag
>> since we do not drop any inmem pages for atomic file.
>>
>> That patch was trying to eliminate a hole which exists in between
>> filemap_write_and_wait_range and set_inode_flag(, FI_ATOMIC_FILE), where GC can
>> still dirty page in the inode, it can pollute isolation of database transaction,
>> so that is why we need this lock.
> 
> Ah, GC can generate any dirty pages of atomic_written data before starting
> another transaction, right?

Yes,

> 
> I think we can do
>  - set_inode_flag() first, followed by
>  - filemap_write_and_wait_range().

If there is redirty flow during filemap_write_and_wait_range, the page can be
register as inmem one?

f2fs_set_data_page_dirty()
...
	if (f2fs_is_atomic_file(inode) && !f2fs_is_commit_atomic_write(inode)) {
		if (!IS_ATOMIC_WRITTEN_PAGE(page)) {
			f2fs_register_inmem_page(inode, page);
			return 1;
		}

Another concern is set_inode_flag and filemap_write_and_wait_range can be
reorder by CPU pipeline, so the serial should be?

set_inode_flag(, FI_ATOMIC_COMMIT)
smp_mb()
set_inode_flag(, FI_ATOMIC_FILE)
smp_mb()

ret = filemap_write_and_wait_range
if (ret)
	goto err_out;

clear_inode_flag(, FI_ATOMIC_COMMIT)

Is that right?

Thanks,

> 
> Thoughts?
> 
>>
>> Thanks,
>>
>>> f2fs_is_atomic_file won't make the page dirty. WDYT?
>>>
>>> Thanks,
>>>
>>>
>>>>
>>>> Thanks,
>>>>
>>>>> -
>>>>>  	if (f2fs_is_atomic_file(inode)) {
>>>>>  		if (is_inode_flag_set(inode, FI_ATOMIC_REVOKE_REQUEST))
>>>>>  			ret = -EINVAL;
>>>>> @@ -1736,7 +1730,6 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)
>>>>>  	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 +1747,9 @@ 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 +1775,6 @@ 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 +2370,10 @@ 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;
>>>>> @@ -2432,6 +2419,14 @@ static int f2fs_move_file_range(struct file *file_in, loff_t pos_in,
>>>>>  
>>>>>  	f2fs_balance_fs(sbi, true);
>>>>>  	f2fs_lock_op(sbi);
>>>>> +
>>>>> +	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;
>>>>> +	}
>>>>> +
>>>>>  	ret = __exchange_data_block(src, dst, pos_in >> F2FS_BLKSIZE_BITS,
>>>>>  				pos_out >> F2FS_BLKSIZE_BITS,
>>>>>  				len >> F2FS_BLKSIZE_BITS, false);
>>>>> @@ -2442,14 +2437,15 @@ static int f2fs_move_file_range(struct file *file_in, loff_t pos_in,
>>>>>  		else if (dst_osize != dst->i_size)
>>>>>  			f2fs_i_size_write(dst, dst_osize);
>>>>>  	}
>>>>> +	if (src != dst)
>>>>> +		up_write(&F2FS_I(dst)->i_gc_rwsem[WRITE]);
>>>>> +out_src:
>>>>> +	up_write(&F2FS_I(src)->i_gc_rwsem[WRITE]);
>>>>>  	f2fs_unlock_op(sbi);
>>>>>  out_unlock:
>>>>> -	if (src != dst) {
>>>>> -		up_write(&F2FS_I(dst)->i_gc_rwsem[WRITE]);
>>>>> +	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)
>>>>>  			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);
>>>>> +
>>>>>  	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: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-07-30  1:32 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 [this message]
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
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
  -- strict thread matches above, loose matches on Subject: below --
2018-07-25  3:22 [PATCH] " Jaegeuk Kim

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	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-kernel


AGPL code for this site: git clone https://public-inbox.org/ public-inbox