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

[Jaegeuk Kim]

Hi Chao,

On Wed, Jan 14, 2015 at 01:01:13PM +0800, Chao Yu wrote:
> Hi Jaegeuk,
> 
> > -----Original Message-----
> > From: Jaegeuk Kim [mailto:jaegeuk@xxxxxxxxxx]
> > Sent: Wednesday, January 14, 2015 8:22 AM
> > To: Chao Yu
> > Cc: 'Changman Lee'; linux-f2fs-devel@xxxxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> > 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@xxxxxxxxxx]
> > > > Sent: Sunday, January 11, 2015 1:32 PM
> > > > To: Chao Yu
> > > > Cc: 'Changman Lee'; linux-f2fs-devel@xxxxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> > > > 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@xxxxxxxxxx]
> > > > > > Sent: Wednesday, January 07, 2015 3:44 AM
> > > > > > To: Chao Yu
> > > > > > Cc: Changman Lee; linux-f2fs-devel@xxxxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> > > > > > 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.

Something like this?