RE: [f2fs-dev] [PATCH 07/11] f2fs: enable in-place-update for fdatasync

[Chao Yu]

Hi Jaegeuk Changman,

> -----Original Message-----
> From: Jaegeuk Kim [mailto:jaegeuk@xxxxxxxxxx]
> Sent: Wednesday, July 30, 2014 9:08 AM
> To: Changman Lee
> Cc: linux-fsdevel@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> linux-f2fs-devel@xxxxxxxxxxxxxxxxxxxxx
> Subject: Re: [f2fs-dev] [PATCH 07/11] f2fs: enable in-place-update for fdatasync
> 
> On Wed, Jul 30, 2014 at 08:54:55AM +0900, Changman Lee wrote:
> > On Tue, Jul 29, 2014 at 05:22:15AM -0700, Jaegeuk Kim wrote:
> > > Hi Changman,
> > >
> > > On Tue, Jul 29, 2014 at 09:41:11AM +0900, Changman Lee wrote:
> > > > Hi Jaegeuk,
> > > >
> > > > On Fri, Jul 25, 2014 at 03:47:21PM -0700, Jaegeuk Kim wrote:
> > > > > This patch enforces in-place-updates only when fdatasync is requested.
> > > > > If we adopt this in-place-updates for the fdatasync, we can skip to write the
> > > > > recovery information.
> > > >
> > > > But, as you know, random write occurs when changing into in-place-updates.
> > > > It will degrade write performance. Is there any case in-place-updates is
> > > > better, except recovery or high utilization?
> > >
> > > As I described, you can easily imagine, if users requested small amount of data
> > > writes with fdatasync, we should do data writes + node writes.
> > > But, if we can do in-place-update, we don't need to write node blocks.
> > > Surely it triggers random writes, however, the amount of data is preety small
> > > and the device handles them very fast by its inside cache, so that it can
> > > enhance the performance.
> > >
> > > Thanks,
> >
> > Partially agree. Sometimes, I see that SSR shows lower performance than
> > IPU. One of the reasons might be node writes.
> 
> What did you mean? That's why I consider IPU eagarly instead of SSR and LFS
> under the very strict cases.
> 
> > Anyway, if so, we should know total dirty pages for fdatasync and it's very
> > tunable according to a random write performance of device.
> 
> Agreed. We can do that either by comparing the number of dirty pages,
> additional data/node writes, and cost of checkpoint at the same time.
> And there is another thing is that we need to consider the number of
> waiting time for end_io.
> I'll look into this at some time.

Agreed, but please additionally consider that the number we got is not highly
accurate because without protection of ->i_mutex writer could generate more
dirty pages.

> 
> Thanks,
> 
> >
> > Thanks,
> >
> > >
> > > >
> > > > Thanks
> > > >
> > > > >
> > > > > Signed-off-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
> > > > > ---
> > > > >  fs/f2fs/f2fs.h    | 1 +
> > > > >  fs/f2fs/file.c    | 7 +++++++
> > > > >  fs/f2fs/segment.h | 4 ++++
> > > > >  3 files changed, 12 insertions(+)
> > > > >
> > > > > diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> > > > > index ab36025..8f8685e 100644
> > > > > --- a/fs/f2fs/f2fs.h
> > > > > +++ b/fs/f2fs/f2fs.h
> > > > > @@ -998,6 +998,7 @@ enum {
> > > > >  	FI_INLINE_DATA,		/* used for inline data*/
> > > > >  	FI_APPEND_WRITE,	/* inode has appended data */
> > > > >  	FI_UPDATE_WRITE,	/* inode has in-place-update data */
> > > > > +	FI_NEED_IPU,		/* used fo ipu for fdatasync */
> > > > >  };
> > > > >
> > > > >  static inline void set_inode_flag(struct f2fs_inode_info *fi, int flag)
> > > > > diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> > > > > index 121689a..e339856 100644
> > > > > --- a/fs/f2fs/file.c
> > > > > +++ b/fs/f2fs/file.c
> > > > > @@ -127,11 +127,18 @@ int f2fs_sync_file(struct file *file, loff_t start, loff_t end,
> int datasync)
> > > > >  		return 0;
> > > > >
> > > > >  	trace_f2fs_sync_file_enter(inode);
> > > > > +
> > > > > +	/* if fdatasync is triggered, let's do in-place-update */
> > > > > +	if (datasync)
> > > > > +		set_inode_flag(fi, FI_NEED_IPU);
> > > > > +
> > > > >  	ret = filemap_write_and_wait_range(inode->i_mapping, start, end);
> > > > >  	if (ret) {
> > > > >  		trace_f2fs_sync_file_exit(inode, need_cp, datasync, ret);
> > > > >  		return ret;
> > > > >  	}
> > > > > +	if (datasync)
> > > > > +		clear_inode_flag(fi, FI_NEED_IPU);
> > > > >
> > > > >  	/*
> > > > >  	 * if there is no written data, don't waste time to write recovery info.
> > > > > diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
> > > > > index ee5c75e..55973f7 100644
> > > > > --- a/fs/f2fs/segment.h
> > > > > +++ b/fs/f2fs/segment.h
> > > > > @@ -486,6 +486,10 @@ static inline bool need_inplace_update(struct inode *inode)
> > > > >  	if (S_ISDIR(inode->i_mode))
> > > > >  		return false;
> > > > >
> > > > > +	/* this is only set during fdatasync */
> > > > > +	if (is_inode_flag_set(F2FS_I(inode), FI_NEED_IPU))
> > > > > +		return true;
> > > > > +
> > > > >  	switch (SM_I(sbi)->ipu_policy) {
> > > > >  	case F2FS_IPU_FORCE:
> > > > >  		return true;
> > > > > --
> > > > > 1.8.5.2 (Apple Git-48)
> > > > >
> > > > >
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