linux-kernel - Re: [f2fs-dev][PATCH 2/2] f2fs: enable recover_xattr_data to avoid cp when fsync after operating xattr

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Date:	Sat, 10 Jan 2015 21:32:12 -0800
From:	Jaegeuk Kim <jaegeuk@...nel.org>
To:	Chao Yu <chao2.yu@...sung.com>
Cc:	'Changman Lee' <cm224.lee@...sung.com>,
	linux-f2fs-devel@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org
Subject: Re: [f2fs-dev][PATCH 2/2] f2fs: enable recover_xattr_data to avoid
 cp when fsync after operating xattr

On Sat, Jan 10, 2015 at 08:08:33PM +0800, Chao Yu wrote:
> Hi Jaegeuk,
> 
> > -----Original Message-----
> > From: Jaegeuk Kim [mailto:jaegeuk@...nel.org]
> > Sent: Wednesday, January 07, 2015 3:44 AM
> > To: Chao Yu
> > Cc: Changman Lee; linux-f2fs-devel@...ts.sourceforge.net; linux-kernel@...r.kernel.org
> > Subject: Re: [f2fs-dev][PATCH 2/2] f2fs: enable recover_xattr_data to avoid cp when fsync after
> > operating xattr
> > 
> > Hi Chao,
> > 
> > On Tue, Jan 06, 2015 at 02:29:40PM +0800, Chao Yu wrote:
> > > Now if we call fsync() after we update the xattr date belongs to the file, f2fs
> > > will do checkpoint to keep data.
> > > This can cause low performance because checkpoint block most operation and write
> > > lots of blocks. So we'd better to avoid doing checkpoint by writing modified
> > > xattr node page to warm node segment, and then it can be recovered when we mount
> > > this device later on.
> > 
> > You're trying to change the writing policy as xattr blocks are written into
> > WARM_NODE area instead of COLD_NODE area.
> > I don't think xattrs are frequently changed between each fsync calls.
> > 
> > How do you think?
> 
> I'm not sure whether there is a scenario that setxattr and fsync are invoked
> alternately, but if there is, our performance will decrease obviously.
> 
> If you don't want to change writing policy, how about writing xattr node with
> fsync flag into cold node segment when fsync() is called, then try to recover
> it from cold node chain when recovery after abnormally pow-cut, this way can
> avoid cp frequently in above scenario.

Firt of all, I don't think this scenario is frequent enough that we have to
break the exisiting writing and recovery procedures.
Moreover, if xattr entries are covered by inline_xattr, it doesn't trigger
checkpoint.

Let me know, if I'm missing something.

If you try to change the recovery procedure, it needs to think about the
disk full condition. (i.e., space_for_roll_forward())
And, I don't want to search cold node chain.

Thanks,

> 
> Thanks,
> Yu
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