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

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

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.

> 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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