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Date:   Wed, 31 Jul 2019 21:14:35 -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: <20190801041435.GB84433@jaegeuk-macbookpro.roam.corp.google.com>
References: <20190719073903.9138-1-yuchao0@huawei.com>
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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
to preallocate blocks, but it can eat disk space unnecessarily.

> 
> 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?

> 
> > 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.

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