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Date:   Thu, 1 Aug 2019 15:27:46 -0700
From:   Jaegeuk Kim <jaegeuk@kernel.org>
To:     Chao Yu <yuchao0@huawei.com>
Cc:     linux-f2fs-devel@lists.sourceforge.net,
        linux-kernel@vger.kernel.org, chao@kernel.org
Subject: Re: [PATCH v2] f2fs: separate NOCoW and pinfile semantics
Message-ID: <20190801222746.GA27597@jaegeuk-macbookpro.roam.corp.google.com>
References: <20190719073903.9138-1-yuchao0@huawei.com>
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On 08/01, Chao Yu wrote:
> 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.

Will be back again tho.

> 
> > 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.

Sometimes it can be large enough for system. If it's from user apps and short
lived, why do we need preallocation?

> 
> > 
> >>
> >> 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
> >>>>>>> .
> >>>>>>>
> >>>>> .
> >>>>>
> >>> .
> >>>
> > .
> >