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Subject: Re: [PATCH v2] f2fs: separate NOCoW and pinfile semantics
To:     Jaegeuk Kim <jaegeuk@kernel.org>
CC:     <linux-f2fs-devel@lists.sourceforge.net>,
        <linux-kernel@vger.kernel.org>, <chao@kernel.org>
References: <20190719073903.9138-1-yuchao0@huawei.com>
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 <20190729055738.GA95664@jaegeuk-macbookpro.roam.corp.google.com>
 <07cd3aba-3516-9ba5-286e-277abb98e244@huawei.com>
 <20190730180231.GB76478@jaegeuk-macbookpro.roam.corp.google.com>
 <00e70eb1-c4fa-a6c9-69d7-71ff995c7d6c@huawei.com>
 <20190801041435.GB84433@jaegeuk-macbookpro.roam.corp.google.com>
From:   Chao Yu <yuchao0@huawei.com>
Message-ID: <d35d5ad7-5622-fbf5-5853-e541f8c26670@huawei.com>
Date:   Thu, 1 Aug 2019 15:08:39 +0800
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On 2019/8/1 12:14, Jaegeuk Kim wrote:
> On 07/31, Chao Yu wrote:
>> On 2019/7/31 2:02, Jaegeuk Kim wrote:
>>> On 07/29, Chao Yu wrote:
>>>> On 2019/7/29 13:57, Jaegeuk Kim wrote:
>>>>> On 07/23, Chao Yu wrote:
>>>>>> On 2019/7/23 10:36, Jaegeuk Kim wrote:
>>>>>>> On 07/19, Chao Yu wrote:
>>>>>>>> Pinning a file is heavy, because skipping pinned files make GC
>>>>>>>> running with heavy load or no effect.
>>>>>>>
>>>>>>> Pinned file is a part of NOCOW files, so I don't think we can simply drop it
>>>>>>> for backward compatibility.
>>>>>>
>>>>>> Yes,
>>>>>>
>>>>>> But what I concerned is that pin file is too heavy, so in order to satisfy below
>>>>>> demand, how about introducing pin_file_2 flag to triggering IPU only during
>>>>>> flush/writeback.
>>>>>
>>>>> That can be done by cold files?
>>>>
>>>> Then it may inherit property of cold type file, e.g. a) goes into cold area; b)
>>>> update with very low frequency.
>>>>
>>>> Actually pin_file_2 could be used by db-wal/log file, which are updated
>>>> frequently, and should go to hot/warm area, it does not match above two property.
>>>
>>> How about considering another name like "IPU-only mode"?
>>>
>>>               fallocate         write    Flag         GC
>>> Pin_file:     preallocate       IPU      FS_NOCOW_FL  Not allowed
>>> IPU_file:     Not preallocate   IPU      N/A          Default by temperature
>>
>> One question, do we need preallocate physical block address for IPU_file as
>> Pin_file? since it can enhance db file's sequential read performance, not sure,
>> db can handle random data in preallocated blocks.
> 
> db file will do atomic writes, which can not be used with this. -wal may be able

Now WAL mode were set by default in Android, so most of db file are -wal type now.

> to preallocate blocks, but it can eat disk space unnecessarily.

I meant .db-wal file rather than .db.

Yes, that's ext4 style, that would bring better performance due to less holes in
block distribution.

I don't think we need to worry about space issue for db-wal file. I tracked
.db-wal file's update before:
- there are very frequently truncation and deletion, that means the preallocated
blocks won't exist for long time.
- and also there are very frequently append writes, I suspect there almost very
few preallocate block are not written.
- total db-wal file number is less.

> 
>>
>> Other behaviors looks good to me. :)
>>
>> I plan to use last bit in inode.i_inline to store this flag.
> 
> Why not using i_flag like FS_NOCOW_FL?

Oops, as you listed in last email, I can see you don't want to break
FS_NOCOW_FL's semantics for backward compatibility.

			Flag
IPU_file		N/A			

If we plan to use FS_NOCOW_FL, that's what this patch has already did, you can
merge it directly... :P

> 
>>
>>> Cold_file:    Not preallocate   IPU      N/A          Move in cold area
>>> Hot_file:     Not preallocate   IPU/OPU  N/A          Move in hot area
>>
>> Should hot file be gced to hot area? That would mix new hot data with old 'hot'
>> data which actually become cold.
> 
> But, user explicitly specified this is hot.

With current implementation, GC will migrate data from hot/warm/cold area to
cold area.

Thanks,

> 
>>
>> Thanks,
>>
>>>
>>>>
>>>> Thank,
>>>>
>>>>>
>>>>>>
>>>>>>>
>>>>>>>>
>>>>>>>> So that this patch propose to separate nocow and pinfile semantics:
>>>>>>>> - NOCoW flag can only be set on regular file.
>>>>>>>> - NOCoW file will only trigger IPU at common writeback/flush.
>>>>>>>> - NOCow file will do OPU during GC.
>>>>>>>>
>>>>>>>> For the demand of 1) avoid fragment of file's physical block and
>>>>>>>> 2) userspace don't care about file's specific physical address,
>>>>>>>> tagging file as NOCoW will be cheaper than pinned one.
>>>>>>
>>>>>> ^^^
>>>>>>
>>>>>> Thanks,
>>>>>>
>>>>>>>>
>>>>>>>> Signed-off-by: Chao Yu <yuchao0@huawei.com>
>>>>>>>> ---
>>>>>>>> v2:
>>>>>>>> - rebase code to fix compile error.
>>>>>>>>  fs/f2fs/data.c |  3 ++-
>>>>>>>>  fs/f2fs/f2fs.h |  1 +
>>>>>>>>  fs/f2fs/file.c | 22 +++++++++++++++++++---
>>>>>>>>  3 files changed, 22 insertions(+), 4 deletions(-)
>>>>>>>>
>>>>>>>> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
>>>>>>>> index a2a28bb269bf..15fb8954c363 100644
>>>>>>>> --- a/fs/f2fs/data.c
>>>>>>>> +++ b/fs/f2fs/data.c
>>>>>>>> @@ -1884,7 +1884,8 @@ static inline bool check_inplace_update_policy(struct inode *inode,
>>>>>>>>  
>>>>>>>>  bool f2fs_should_update_inplace(struct inode *inode, struct f2fs_io_info *fio)
>>>>>>>>  {
>>>>>>>> -	if (f2fs_is_pinned_file(inode))
>>>>>>>> +	if (f2fs_is_pinned_file(inode) ||
>>>>>>>> +			F2FS_I(inode)->i_flags & F2FS_NOCOW_FL)
>>>>>>>>  		return true;
>>>>>>>>  
>>>>>>>>  	/* if this is cold file, we should overwrite to avoid fragmentation */
>>>>>>>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>>>>>>>> index 596ab3e1dd7b..f6c5a3d2e659 100644
>>>>>>>> --- a/fs/f2fs/f2fs.h
>>>>>>>> +++ b/fs/f2fs/f2fs.h
>>>>>>>> @@ -2374,6 +2374,7 @@ static inline void f2fs_change_bit(unsigned int nr, char *addr)
>>>>>>>>  #define F2FS_NOATIME_FL			0x00000080 /* do not update atime */
>>>>>>>>  #define F2FS_INDEX_FL			0x00001000 /* hash-indexed directory */
>>>>>>>>  #define F2FS_DIRSYNC_FL			0x00010000 /* dirsync behaviour (directories only) */
>>>>>>>> +#define F2FS_NOCOW_FL			0x00800000 /* Do not cow file */
>>>>>>>>  #define F2FS_PROJINHERIT_FL		0x20000000 /* Create with parents projid */
>>>>>>>>  
>>>>>>>>  /* Flags that should be inherited by new inodes from their parent. */
>>>>>>>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
>>>>>>>> index 7ca545874060..ae0fec54cac6 100644
>>>>>>>> --- a/fs/f2fs/file.c
>>>>>>>> +++ b/fs/f2fs/file.c
>>>>>>>> @@ -1692,6 +1692,7 @@ static const struct {
>>>>>>>>  	{ F2FS_NOATIME_FL,	FS_NOATIME_FL },
>>>>>>>>  	{ F2FS_INDEX_FL,	FS_INDEX_FL },
>>>>>>>>  	{ F2FS_DIRSYNC_FL,	FS_DIRSYNC_FL },
>>>>>>>> +	{ F2FS_NOCOW_FL,	FS_NOCOW_FL },
>>>>>>>>  	{ F2FS_PROJINHERIT_FL,	FS_PROJINHERIT_FL },
>>>>>>>>  };
>>>>>>>>  
>>>>>>>> @@ -1715,7 +1716,8 @@ static const struct {
>>>>>>>>  		FS_NODUMP_FL |		\
>>>>>>>>  		FS_NOATIME_FL |		\
>>>>>>>>  		FS_DIRSYNC_FL |		\
>>>>>>>> -		FS_PROJINHERIT_FL)
>>>>>>>> +		FS_PROJINHERIT_FL |	\
>>>>>>>> +		FS_NOCOW_FL)
>>>>>>>>  
>>>>>>>>  /* Convert f2fs on-disk i_flags to FS_IOC_{GET,SET}FLAGS flags */
>>>>>>>>  static inline u32 f2fs_iflags_to_fsflags(u32 iflags)
>>>>>>>> @@ -1753,8 +1755,6 @@ static int f2fs_ioc_getflags(struct file *filp, unsigned long arg)
>>>>>>>>  		fsflags |= FS_ENCRYPT_FL;
>>>>>>>>  	if (f2fs_has_inline_data(inode) || f2fs_has_inline_dentry(inode))
>>>>>>>>  		fsflags |= FS_INLINE_DATA_FL;
>>>>>>>> -	if (is_inode_flag_set(inode, FI_PIN_FILE))
>>>>>>>> -		fsflags |= FS_NOCOW_FL;
>>>>>>>>  
>>>>>>>>  	fsflags &= F2FS_GETTABLE_FS_FL;
>>>>>>>>  
>>>>>>>> @@ -1794,6 +1794,22 @@ static int f2fs_ioc_setflags(struct file *filp, unsigned long arg)
>>>>>>>>  	if (ret)
>>>>>>>>  		goto out;
>>>>>>>>  
>>>>>>>> +	if ((fsflags ^ old_fsflags) & FS_NOCOW_FL) {
>>>>>>>> +		if (!S_ISREG(inode->i_mode)) {
>>>>>>>> +			ret = -EINVAL;
>>>>>>>> +			goto out;
>>>>>>>> +		}
>>>>>>>> +
>>>>>>>> +		if (f2fs_should_update_outplace(inode, NULL)) {
>>>>>>>> +			ret = -EINVAL;
>>>>>>>> +			goto out;
>>>>>>>> +		}
>>>>>>>> +
>>>>>>>> +		ret = f2fs_convert_inline_inode(inode);
>>>>>>>> +		if (ret)
>>>>>>>> +			goto out;
>>>>>>>> +	}
>>>>>>>> +
>>>>>>>>  	ret = f2fs_setflags_common(inode, iflags,
>>>>>>>>  			f2fs_fsflags_to_iflags(F2FS_SETTABLE_FS_FL));
>>>>>>>>  out:
>>>>>>>> -- 
>>>>>>>> 2.18.0.rc1
>>>>>>> .
>>>>>>>
>>>>> .
>>>>>
>>> .
>>>
> .
>