Re: [f2fs-dev] [PATCH] f2fs: add cleancache support

[Changman Lee <cm224.lee@samsung.com>]

On Fri, Nov 14, 2014 at 02:53:02PM +0900, Changman Lee wrote:
> On Thu, Nov 13, 2014 at 05:27:51PM -0800, Jaegeuk Kim wrote:
> > Hi Changman,
> > 
> > On Thu, Nov 13, 2014 at 02:34:50PM +0900, Changman Lee wrote:
> > > To use cleancache, fs must explicitly enable cleancache by calling
> > > cleancache_init_fs.
> > 
> > Good catch!
> > 
> > Prior to merge this patch, can you share any testing results or performance
> > numbers?
> > 
> Not yet, I'll try to get numbers.
> 

Hi,

This is the result of kernel compile on xen-4.4 enabled tmem
: cleancache and frontswap.
I'm afraid that there is little difference by cleancache.
The cleancache shows a few cache hits but the effect through it doesn't
show. I don't know best benchmark to testify it yet.
Finally, I couldn't discover any bug during test.

[before patch]
		1		2		3
Elapsed time	25:00.67	25:07.09	25:00.38
Major fault	31100		31410		31333
Minor fault	276869398	276869318	276871144

[after patch]
		1		2		3
Elapsed time	25:12.34	25:13.29	25:11.99
Major fault	31559		32069		31801
Minor fault	276870283	276868046	276869251

[cleancache] - diff between start and end
		1		2		3
failed_gets	1277980		1296355		1300368
invalidates	2588227		2651722		2655285
puts		1289970		1323685		1320623
*succ_gets*	111111		121299		114310

Thanks,
Changman

> > What condition will be the best way to exploit f2fs and cleancache?
> > 
> Not clear.
> I think we can make a cleancache client for f2fs so that can compenstate
> a penalty of node pages which are read mostly.
> 
> > Can we confirm that f2fs satisfies most of requirements described by
> > cleancache.txt below?
> 
> Good point.
> At a quick glance, F2FS seems to satisfy most of requirements.
> Through a experimental, I'll try to check side effect.
> 
> > 
> > Some points for a filesystem to consider:
> > 
> > - The FS should be block-device-based (e.g. a ram-based FS such
> >   as tmpfs should not enable cleancache)
> > - To ensure coherency/correctness, the FS must ensure that all
> >   file removal or truncation operations either go through VFS or
> >   add hooks to do the equivalent cleancache "invalidate" operations
> > - To ensure coherency/correctness, either inode numbers must
> >   be unique across the lifetime of the on-disk file OR the
> >   FS must provide an "encode_fh" function.
> > - The FS must call the VFS superblock alloc and deactivate routines
> >   or add hooks to do the equivalent cleancache calls done there.
> > - To maximize performance, all pages fetched from the FS should
> >   go through the do_mpag_readpage routine or the FS should add
> >   hooks to do the equivalent (cf. btrfs)
> > - Currently, the FS blocksize must be the same as PAGESIZE.  This
> >   is not an architectural restriction, but no backends currently
> >   support anything different.
> > - A clustered FS should invoke the "shared_init_fs" cleancache
> >   hook to get best performance for some backends.
> > 
> > Thanks,
> > 
> > > 
> > > Signed-off-by: Changman Lee <cm224.lee@samsung.com>
> > > ---
> > >  fs/f2fs/super.c | 3 +++
> > >  1 file changed, 3 insertions(+)
> > > 
> > > diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
> > > index 512ffd8..2ebb960 100644
> > > --- a/fs/f2fs/super.c
> > > +++ b/fs/f2fs/super.c
> > > @@ -24,6 +24,7 @@
> > >  #include <linux/blkdev.h>
> > >  #include <linux/f2fs_fs.h>
> > >  #include <linux/sysfs.h>
> > > +#include <linux/cleancache.h>
> > >  
> > >  #include "f2fs.h"
> > >  #include "node.h"
> > > @@ -1144,6 +1145,8 @@ try_onemore:
> > >  		if (err)
> > >  			goto free_kobj;
> > >  	}
> > > +
> > > +	cleancache_init_fs(sb);
> > >  	return 0;
> > >  
> > >  free_kobj:
> > > -- 
> > > 1.9.1
> > > 
> > > 
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