Re: [PATCH] f2fs: provide f2fs_balance_fs to __write_data_page for dentry pages

[Chao Yu]

Hi Jaegeuk,

On 2017/7/30 15:31, Jaegeuk Kim wrote:
> On 07/29, Yunlong Song wrote:
>> f2fs_balance_fs of dentry pages is skipped in __write_data_page due to deadlock
>> of gc_mutex in write_checkpoint flow. This patch enables f2fs_balance_fs for
>> normal dentry page writeback to ensure there are always enough free segments.
> 
> Sorry, by the way, why do we need to do this? I subtly thought that dirty node
> pages can be produce by redirtied inodes from what we've not covered through
> filesystem calls. But, in dentry pages, we're controlling the number of dirty
> pages, and calling f2fs_balance_fs in each directory operations.

IMO, writebacking dentry page can redirty dnode page which may be clean previously,
so it will be more safe to call f2fs_balance_fs to make sure dirty metadatas of
filesystem didn't exceed the threshold.

Thanks,

> 
> Chao?
> 
> Thanks,
> 
>>
>> Reported-by: Chao Yu <yuchao0@xxxxxxxxxx>
>> Signed-off-by: Yunlong Song <yunlong.song@xxxxxxxxxx>
>> ---
>>  fs/f2fs/checkpoint.c |  2 +-
>>  fs/f2fs/data.c       | 67 +++++++++++++++++++++++++++++++++++++++++++++-------
>>  fs/f2fs/f2fs.h       |  1 +
>>  3 files changed, 61 insertions(+), 9 deletions(-)
>>
>> diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
>> index 3c84a25..2882878 100644
>> --- a/fs/f2fs/checkpoint.c
>> +++ b/fs/f2fs/checkpoint.c
>> @@ -904,7 +904,7 @@ int sync_dirty_inodes(struct f2fs_sb_info *sbi, enum inode_type type)
>>  	if (inode) {
>>  		unsigned long cur_ino = inode->i_ino;
>>  
>> -		filemap_fdatawrite(inode->i_mapping);
>> +		f2fs_filemap_fdatawrite(inode->i_mapping, is_dir);
>>  		iput(inode);
>>  		/* We need to give cpu to another writers. */
>>  		if (ino == cur_ino) {
>> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
>> index aefc2a5..ed7efa5 100644
>> --- a/fs/f2fs/data.c
>> +++ b/fs/f2fs/data.c
>> @@ -1475,7 +1475,7 @@ int do_write_data_page(struct f2fs_io_info *fio)
>>  }
>>  
>>  static int __write_data_page(struct page *page, bool *submitted,
>> -				struct writeback_control *wbc)
>> +				struct writeback_control *wbc, bool do_balance)
>>  {
>>  	struct inode *inode = page->mapping->host;
>>  	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
>> @@ -1578,7 +1578,7 @@ static int __write_data_page(struct page *page, bool *submitted,
>>  	}
>>  
>>  	unlock_page(page);
>> -	if (!S_ISDIR(inode->i_mode))
>> +	if (do_balance)
>>  		f2fs_balance_fs(sbi, need_balance_fs);
>>  
>>  	if (unlikely(f2fs_cp_error(sbi))) {
>> @@ -1602,7 +1602,7 @@ static int __write_data_page(struct page *page, bool *submitted,
>>  static int f2fs_write_data_page(struct page *page,
>>  					struct writeback_control *wbc)
>>  {
>> -	return __write_data_page(page, NULL, wbc);
>> +	return __write_data_page(page, NULL, wbc, true);
>>  }
>>  
>>  /*
>> @@ -1611,7 +1611,7 @@ static int f2fs_write_data_page(struct page *page,
>>   * warm/hot data page.
>>   */
>>  static int f2fs_write_cache_pages(struct address_space *mapping,
>> -					struct writeback_control *wbc)
>> +					struct writeback_control *wbc, bool do_balance)
>>  {
>>  	int ret = 0;
>>  	int done = 0;
>> @@ -1701,7 +1701,7 @@ static int f2fs_write_cache_pages(struct address_space *mapping,
>>  			if (!clear_page_dirty_for_io(page))
>>  				goto continue_unlock;
>>  
>> -			ret = __write_data_page(page, &submitted, wbc);
>> +			ret = __write_data_page(page, &submitted, wbc, do_balance);
>>  			if (unlikely(ret)) {
>>  				/*
>>  				 * keep nr_to_write, since vfs uses this to
>> @@ -1756,8 +1756,8 @@ static int f2fs_write_cache_pages(struct address_space *mapping,
>>  	return ret;
>>  }
>>  
>> -static int f2fs_write_data_pages(struct address_space *mapping,
>> -			    struct writeback_control *wbc)
>> +static int _f2fs_write_data_pages(struct address_space *mapping,
>> +			    struct writeback_control *wbc, bool do_balance)
>>  {
>>  	struct inode *inode = mapping->host;
>>  	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
>> @@ -1794,7 +1794,7 @@ static int f2fs_write_data_pages(struct address_space *mapping,
>>  		goto skip_write;
>>  
>>  	blk_start_plug(&plug);
>> -	ret = f2fs_write_cache_pages(mapping, wbc);
>> +	ret = f2fs_write_cache_pages(mapping, wbc, do_balance);
>>  	blk_finish_plug(&plug);
>>  
>>  	if (wbc->sync_mode == WB_SYNC_ALL)
>> @@ -1813,6 +1813,57 @@ static int f2fs_write_data_pages(struct address_space *mapping,
>>  	return 0;
>>  }
>>  
>> +static int f2fs_write_data_pages(struct address_space *mapping,
>> +			    struct writeback_control *wbc)
>> +{
>> +	return	_f2fs_write_data_pages(mapping, wbc, true);
>> +}
>> +
>> +/*
>> + * This function was copied from do_writepages from mm/page-writeback.c.
>> + * The major change is changing writepages to _f2fs_write_data_pages.
>> + */
>> +static int f2fs_do_writepages(struct address_space *mapping,
>> +				struct writeback_control *wbc, bool is_dir)
>> +{
>> +	int ret;
>> +
>> +	if (wbc->nr_to_write <= 0)
>> +		return 0;
>> +	while (1) {
>> +		ret = _f2fs_write_data_pages(mapping, wbc, !is_dir);
>> +		if ((ret != -ENOMEM) || (wbc->sync_mode != WB_SYNC_ALL))
>> +			break;
>> +		cond_resched();
>> +		congestion_wait(BLK_RW_ASYNC, HZ/50);
>> +	}
>> +	return ret;
>> +}
>> +
>> +/*
>> + * This function was copied from __filemap_fdatawrite_range from
>> + * mm/filemap.c. The major change is changing do_writepages to
>> + * f2fs_do_writepages.
>> + */
>> +int f2fs_filemap_fdatawrite(struct address_space *mapping, bool is_dir)
>> +{
>> +	int ret;
>> +	struct writeback_control wbc = {
>> +		.sync_mode = WB_SYNC_ALL,
>> +		.nr_to_write = LONG_MAX,
>> +		.range_start = 0,
>> +		.range_end = LLONG_MAX,
>> +	};
>> +
>> +	if (!mapping_cap_writeback_dirty(mapping))
>> +		return 0;
>> +
>> +	wbc_attach_fdatawrite_inode(&wbc, mapping->host);
>> +	ret = f2fs_do_writepages(mapping, &wbc, is_dir);
>> +	wbc_detach_inode(&wbc);
>> +	return ret;
>> +}
>> +
>>  static void f2fs_write_failed(struct address_space *mapping, loff_t to)
>>  {
>>  	struct inode *inode = mapping->host;
>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>> index 9280283..ea9bebb 100644
>> --- a/fs/f2fs/f2fs.h
>> +++ b/fs/f2fs/f2fs.h
>> @@ -2572,6 +2572,7 @@ void f2fs_invalidate_page(struct page *page, unsigned int offset,
>>  int f2fs_migrate_page(struct address_space *mapping, struct page *newpage,
>>  			struct page *page, enum migrate_mode mode);
>>  #endif
>> +int f2fs_filemap_fdatawrite(struct address_space *mapping, bool is_dir);
>>  
>>  /*
>>   * gc.c
>> -- 
>> 1.8.5.2