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

[Chao Yu]

Hi Jaegeuk,

> -----Original Message-----
> From: Jaegeuk Kim [mailto:jaegeuk@xxxxxxxxxx]
> Sent: Friday, January 23, 2015 7:13 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 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?

It's good, this is what I wanted.
Thanks for your work! :)

> 
> From 6b609421e4f9f52de26554300aae62de33e0703a Mon Sep 17 00:00:00 2001
> From: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
> Date: Thu, 22 Jan 2015 14:48:28 -0800
> Subject: [PATCH] f2fs: leave comment for code readability
> 
> During the recovery, any xattr blocks should not be found, since they are
> written into cold log, not the warm node chain.
> 
> Signed-off-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>

Reviewed-by: Chao Yu <chao2.yu@xxxxxxxxxxx>

Thanks,
Yu

> ---
>  fs/f2fs/recovery.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/fs/f2fs/recovery.c b/fs/f2fs/recovery.c
> index c4211a5..57603a7 100644
> --- a/fs/f2fs/recovery.c
> +++ b/fs/f2fs/recovery.c
> @@ -346,6 +346,10 @@ static int do_recover_data(struct f2fs_sb_info *sbi, struct inode *inode,
>  	if (IS_INODE(page)) {
>  		recover_inline_xattr(inode, page);
>  	} else if (f2fs_has_xattr_block(ofs_of_node(page))) {
> +		/*
> +		 * Deprecated; xattr blocks should be found from cold log.
> +		 * But, we should remain this for backward compatibility.
> +		 */
>  		recover_xattr_data(inode, page, blkaddr);
>  		goto out;
>  	}
> --
> 2.1.1

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