Re: [RFC PATCH 1/2] bdi: Create a flag to indicate that a backing device needs stable page writes

[Jan Kara <jack@suse.cz>]

On Mon 29-10-12 19:13:58, Jan Kara wrote:
> On Fri 26-10-12 18:35:24, Darrick J. Wong wrote:
> > This creates BDI_CAP_STABLE_WRITES, which indicates that a device requires
> > stable page writes.  It also plumbs in a sysfs attribute so that admins can
> > check the device status.
> > 
> > Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
>   I guess Jens Axboe <axboe@kernel.dk> would be the best target for this
> patch (so that he can merge it). The patch looks OK to me. You can add:
>   Reviewed-by: Jan Kara <jack@suse.cz>
  One more thing popped up in my mind: What about NFS, Ceph or md RAID5?
These could (at least theoretically) care about stable writes as well. I'm
not sure if they really started to use them but it would be good to at
least let them know.

								Honza

> > ---
> > 
> >  block/blk-integrity.c       |    8 ++++++++
> >  include/linux/backing-dev.h |    6 ++++++
> >  mm/backing-dev.c            |   11 +++++++++++
> >  3 files changed, 25 insertions(+)
> > 
> > diff --git a/block/blk-integrity.c b/block/blk-integrity.c
> > index da2a818..d05d7b3 100644
> > --- a/block/blk-integrity.c
> > +++ b/block/blk-integrity.c
> > @@ -384,6 +384,7 @@ EXPORT_SYMBOL(blk_integrity_is_initialized);
> >  int blk_integrity_register(struct gendisk *disk, struct blk_integrity *template)
> >  {
> >  	struct blk_integrity *bi;
> > +	struct backing_dev_info *bdi;
> >  
> >  	BUG_ON(disk == NULL);
> >  
> > @@ -420,6 +421,9 @@ int blk_integrity_register(struct gendisk *disk, struct blk_integrity *template)
> >  	} else
> >  		bi->name = bi_unsupported_name;
> >  
> > +	bdi = &disk->queue->backing_dev_info;
> > +	bdi->capabilities |= BDI_CAP_STABLE_WRITES;
> > +
> >  	return 0;
> >  }
> >  EXPORT_SYMBOL(blk_integrity_register);
> > @@ -434,10 +438,14 @@ EXPORT_SYMBOL(blk_integrity_register);
> >  void blk_integrity_unregister(struct gendisk *disk)
> >  {
> >  	struct blk_integrity *bi;
> > +	struct backing_dev_info *bdi;
> >  
> >  	if (!disk || !disk->integrity)
> >  		return;
> >  
> > +	bdi = &disk->queue->backing_dev_info;
> > +	bdi->capabilities &= ~BDI_CAP_STABLE_WRITES;
> > +
> >  	bi = disk->integrity;
> >  
> >  	kobject_uevent(&bi->kobj, KOBJ_REMOVE);
> > diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
> > index 2a9a9ab..b82a8bb 100644
> > --- a/include/linux/backing-dev.h
> > +++ b/include/linux/backing-dev.h
> > @@ -253,6 +253,7 @@ int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned int max_ratio);
> >  #define BDI_CAP_EXEC_MAP	0x00000040
> >  #define BDI_CAP_NO_ACCT_WB	0x00000080
> >  #define BDI_CAP_SWAP_BACKED	0x00000100
> > +#define BDI_CAP_STABLE_WRITES	0x00000200
> >  
> >  #define BDI_CAP_VMFLAGS \
> >  	(BDI_CAP_READ_MAP | BDI_CAP_WRITE_MAP | BDI_CAP_EXEC_MAP)
> > @@ -307,6 +308,11 @@ long wait_iff_congested(struct zone *zone, int sync, long timeout);
> >  int pdflush_proc_obsolete(struct ctl_table *table, int write,
> >  		void __user *buffer, size_t *lenp, loff_t *ppos);
> >  
> > +static inline bool bdi_cap_stable_writes(struct backing_dev_info *bdi)
> > +{
> > +	return bdi->capabilities & BDI_CAP_STABLE_WRITES;
> > +}
> > +
> >  static inline bool bdi_cap_writeback_dirty(struct backing_dev_info *bdi)
> >  {
> >  	return !(bdi->capabilities & BDI_CAP_NO_WRITEBACK);
> > diff --git a/mm/backing-dev.c b/mm/backing-dev.c
> > index d3ca2b3..a2f4c08 100644
> > --- a/mm/backing-dev.c
> > +++ b/mm/backing-dev.c
> > @@ -221,12 +221,23 @@ static ssize_t max_ratio_store(struct device *dev,
> >  }
> >  BDI_SHOW(max_ratio, bdi->max_ratio)
> >  
> > +static ssize_t stable_page_writes_show(struct device *dev,
> > +	struct device_attribute *attr, char *page)
> > +{
> > +	struct backing_dev_info *bdi = dev_get_drvdata(dev);
> > +
> > +	return snprintf(page, PAGE_SIZE-1, "%d\n",
> > +			bdi->capabilities & BDI_CAP_STABLE_WRITES ? 1 : 0);
> > +}
> > +
> >  #define __ATTR_RW(attr) __ATTR(attr, 0644, attr##_show, attr##_store)
> > +#define __ATTR_RO(attr) __ATTR(attr, 0444, attr##_show, NULL)
> >  
> >  static struct device_attribute bdi_dev_attrs[] = {
> >  	__ATTR_RW(read_ahead_kb),
> >  	__ATTR_RW(min_ratio),
> >  	__ATTR_RW(max_ratio),
> > +	__ATTR_RO(stable_page_writes),
> >  	__ATTR_NULL,
> >  };
> >  
> > --
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> -- 
> Jan Kara <jack@suse.cz>
> SUSE Labs, CR
> --
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-- 
Jan Kara <jack@suse.cz>
SUSE Labs, CR