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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Message-id: <008a01d02fb7$3abb2bd0$b0318370$@samsung.com>
Date:	Wed, 14 Jan 2015 13:01:13 +0800
From:	Chao Yu <chao2.yu@...sung.com>
To:	'Jaegeuk Kim' <jaegeuk@...nel.org>
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

Hi Jaegeuk,

> -----Original Message-----
> From: Jaegeuk Kim [mailto:jaegeuk@...nel.org]
> Sent: Wednesday, January 14, 2015 8:22 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
> 
> On Mon, Jan 12, 2015 at 05:40:28PM +0800, Chao Yu wrote:
> > Hi Jaegeuk,
> >
> > > -----Original Message-----
> > > From: Jaegeuk Kim [mailto:jaegeuk@...nel.org]
> > > Sent: Sunday, January 11, 2015 1:32 PM
> > > 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
> > >
> > > 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.
> >
> > Agree, that's a good solution.
> >
> > >
> > > 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.
> >
> > OK, if we keep writing policy and recovery procedure as it is, then, shouldn't our
> > recover_xattr_data be dropped because it will be not used from any call path?
> > How do you think of below patch?
> 
> Hi Chao,
> 
> Nice catch.
> But, IIRC, this code was remained for backward compatibility, since long time
> ago, xattr blocks were written into the warm node chain.

Ah, I got it, thanks for your explanation! :)
How do you think of adding some comments on these codes, because this can help
developers understand it well and not to submit the wrong fix patch like me again.

Thanks,

> So, I couldn't remove this.
> 
> Thanks,


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