Re: [PATCH 1/2] f2fs: detect host-managed SMR by feature flag

[Jaegeuk Kim]

On Wed, Jun 15, 2016 at 04:21:13AM +0000, Damien Le Moal wrote:
> Jaegeuk,
> 
> On 6/15/16 03:45, Jaegeuk Kim wrote:
> > If mkfs.f2fs gives a feature flag for host-managed SMR, we can set mode=lfs
> > by default.
> >
> > Signed-off-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
> > ---
> >  fs/f2fs/f2fs.h  | 21 +++++++++++++++++++++
> >  fs/f2fs/super.c | 14 ++++++++------
> >  2 files changed, 29 insertions(+), 6 deletions(-)
> >
> > diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> > index 32be19e..1a19c02 100644
> > --- a/fs/f2fs/f2fs.h
> > +++ b/fs/f2fs/f2fs.h
> > @@ -133,6 +133,7 @@ struct f2fs_mount_info {
> >  };
> >
> >  #define F2FS_FEATURE_ENCRYPT	0x0001
> > +#define F2FS_FEATURE_HMSMR	0x0002
> >
> >  #define F2FS_HAS_FEATURE(sb, mask)					\
> >  	((F2FS_SB(sb)->raw_super->feature & cpu_to_le32(mask)) != 0)
> > @@ -2354,6 +2355,26 @@ static inline int f2fs_sb_has_crypto(struct super_block *sb)
> >  	return F2FS_HAS_FEATURE(sb, F2FS_FEATURE_ENCRYPT);
> >  }
> >
> > +static inline int f2fs_sb_mounted_hmsmr(struct super_block *sb)
> > +{
> > +	return F2FS_HAS_FEATURE(sb, F2FS_FEATURE_HMSMR);
> > +}
> > +
> > +static inline void set_opt_mode(struct f2fs_sb_info *sbi, unsigned int mt)
> > +{
> > +	clear_opt(sbi, ADAPTIVE);
> > +	clear_opt(sbi, LFS);
> > +
> > +	switch (mt) {
> > +	case F2FS_MOUNT_ADAPTIVE:
> > +		set_opt(sbi, ADAPTIVE);
> > +		break;
> > +	case F2FS_MOUNT_LFS:
> > +		set_opt(sbi, LFS);
> > +		break;
> > +	}
> > +}
> > +
> >  static inline bool f2fs_may_encrypt(struct inode *inode)
> >  {
> >  #ifdef CONFIG_F2FS_FS_ENCRYPTION
> > diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
> > index edc736d..71b6066 100644
> > --- a/fs/f2fs/super.c
> > +++ b/fs/f2fs/super.c
> > @@ -515,12 +515,10 @@ static int parse_options(struct super_block *sb, char *options)
> >  				return -ENOMEM;
> >  			if (strlen(name) == 8 &&
> >  					!strncmp(name, "adaptive", 8)) {
> > -				set_opt(sbi, ADAPTIVE);
> > -				clear_opt(sbi, LFS);
> > +				set_opt_mode(sbi, F2FS_MOUNT_ADAPTIVE);
> >  			} else if (strlen(name) == 3 &&
> >  					!strncmp(name, "lfs", 3)) {
> > -				clear_opt(sbi, ADAPTIVE);
> > -				set_opt(sbi, LFS);
> > +				set_opt_mode(sbi, F2FS_MOUNT_LFS);
> >  			} else {
> >  				kfree(name);
> >  				return -EINVAL;
> > @@ -980,7 +978,10 @@ static void default_options(struct f2fs_sb_info *sbi)
> >  	set_opt(sbi, EXTENT_CACHE);
> >  	sbi->sb->s_flags |= MS_LAZYTIME;
> >  	set_opt(sbi, FLUSH_MERGE);
> > -	set_opt(sbi, ADAPTIVE);
> > +	if (f2fs_sb_mounted_hmsmr(sbi->sb))
> > +		set_opt_mode(sbi, F2FS_MOUNT_LFS);
> > +	else
> > +		set_opt_mode(sbi, F2FS_MOUNT_ADAPTIVE);
> 
> Strictly speaking, host-aware drives would not require the LFS mode
> as any zone of the disk can be randomly written and so the occasional 
> in-place updates of the adaptive mode would be OK. However, randomly 
> writing host-aware drives can lead to a lot of background activity on 
> the drive side for internal management of the accumulated random writes, 
> with a potential performance drop over time (this is highly dependent on 
> the drive FW implementation though).
> 
> So I think it would be good to also enable the LFS mode by default for 
> host-aware devices, unless the user has explicitly specified mount with 
> adaptive mode (if the user "knows" that the drive FW handles very 
> efficiently random writes).

Agreed. Would HASMR also provide the same geometry, zone information, in mkfs?
Cause I haven't tested it so far.

IIRC, we discussed about HASMR with Marc Lehmann last year, and he gave the
below link which sums up.

http://comments.gmane.org/gmane.linux.file-systems.f2fs/2854
http://blog.schmorp.de/2015-10-08-smr-archive-drives-fast-now.html

> So how about also introducing a F2FS_FEATURE_HASMR feature flag to 
> handle these different cases ?

Yes, so once I can retrieve the zone information from the device, surely I'll
add that.

> Also, I think that the DISCARD option must be enabled by default for 
> HMSMR disks. Otherwise, zones write pointer will never get reset.
> The same applies to HASMR devices mounted with the LFS mode.
> (In any case, the discard handling does not look like it will always 
> align to the device zone size, which will fail on a zoned disk (discard 
> granularity is the zone size). I may be missing something though. Still 
> checking.)

Yup, will do. BTW, I remember I fixed zone-aligned discard issue before.
Could you please check the latest dev-test branch in f2fs.git?
I'm used to rebase that branch occasionally when I changed the previous patches.

Thanks,

> 
> Best regards.
> 
> -- 
> Damien Le Moal, Ph.D.
> Sr. Manager, System Software Group, HGST Research,
> HGST, a Western Digital company
> Damien.LeMoal@xxxxxxxx
> (+81) 0466-98-3593 (ext. 513593)
> 1 kirihara-cho, Fujisawa,
> Kanagawa, 252-0888 Japan
> www.hgst.com
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