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 20:08:33 +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 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.

Thanks,
Yu


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