linux-kernel - Re: [RFC v2 PATCH 0/6] Btrfs: Add hot data relocation functionality

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Date:	Mon, 30 Aug 2010 09:05:29 +0800
From:	Shaohua Li <shaohua.li@...el.com>
To:	Hubert Kario <hka@....com.pl>
Cc:	"bchociej@...il.com" <bchociej@...il.com>,
	"chris.mason@...cle.com" <chris.mason@...cle.com>,
	"linux-btrfs@...r.kernel.org" <linux-btrfs@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"cmm@...ibm.com" <cmm@...ibm.com>,
	"bcchocie@...ibm.com" <bcchocie@...ibm.com>,
	"mrlupfer@...ibm.com" <mrlupfer@...ibm.com>,
	"crscott@...ibm.com" <crscott@...ibm.com>,
	"mlupfer@...il.com" <mlupfer@...il.com>,
	"conscott@...edu" <conscott@...edu>
Subject: Re: [RFC v2 PATCH 0/6] Btrfs: Add hot data relocation functionality

On Mon, 2010-08-30 at 08:42 +0800, Hubert Kario wrote:
> On Thursday 26 of August 2010 04:13:43 Shaohua Li wrote:
> > On Fri, Aug 13, 2010 at 06:22:00AM +0800, bchociej@...il.com wrote:
> > > - Hooks in existing Btrfs functions to track data access frequency
> > > 
> > >   (btrfs_direct_IO, btrfs_readpages, and extent_write_cache_pages)
> > > 
> > > - New rbtrees for tracking access frequency of inodes and sub-file
> > > 
> > >   ranges (hotdata_map.c)
> > > 
> > > - A hash list for indexing data by its temperature (hotdata_hash.c)
> > > 
> > > - A debugfs interface for dumping data from the rbtrees (debugfs.c)
> > > 
> > > - A background kthread for relocating data to faster media based on
> > > 
> > >   temperature
> > 
> > Hi,
> > I'm wondering if the temperature info can be exported to userspace, and
> > let a daemon to do the relocation (by ioctl). A userspace daemon is more
> > flexible.
> 
> Flexibility of userspace daemon is one thing, the ability to let the admin 
> precisely control on which drive data is placed could be really beneficial in 
> some scenarios is another thing.
> 
> This would also allow online defragmentation, together with access to 
> statistics, one that (for quick runs) has really good time/performance benefit 
> ratio.
Agreed, I'm thinking of the online defragmentation based on hot access
too. Btrfs usually has more fragment.

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