Re: [PATCH 1/3] bdi: Track users that require stable page writes

[Jan Kara]

On Thu 01-11-12 00:58:13, Darrick J. Wong wrote:
> This creates a per-backing-device counter that tracks the number of users which
> require pages to be held immutable during writeout.  Eventually it will be used
> to waive wait_for_page_writeback() if nobody requires stable pages.
  As I wrote in another mail, maybe a combination of bdi and sb flag would
make things simpler (less chances for errors). But I can live with this as
well...

								Honza
> 
> Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> ---
>  Documentation/ABI/testing/sysfs-class-bdi |    7 +++++
>  block/blk-integrity.c                     |    4 +++
>  include/linux/backing-dev.h               |   16 ++++++++++++
>  include/linux/blkdev.h                    |   10 ++++++++
>  mm/backing-dev.c                          |   38 +++++++++++++++++++++++++++++
>  5 files changed, 75 insertions(+)
> 
> 
> diff --git a/Documentation/ABI/testing/sysfs-class-bdi b/Documentation/ABI/testing/sysfs-class-bdi
> index 5f50097..218a618 100644
> --- a/Documentation/ABI/testing/sysfs-class-bdi
> +++ b/Documentation/ABI/testing/sysfs-class-bdi
> @@ -48,3 +48,10 @@ max_ratio (read-write)
>  	most of the write-back cache.  For example in case of an NFS
>  	mount that is prone to get stuck, or a FUSE mount which cannot
>  	be trusted to play fair.
> +
> +stable_pages_required (read-write)
> +
> +	If set, the backing device requires that all pages comprising a write
> +	request must not be changed until writeout is complete.  The system
> +	administrator can turn this on if the hardware does not do so already.
> +	However, once enabled, this flag cannot be disabled.
> diff --git a/block/blk-integrity.c b/block/blk-integrity.c
> index da2a818..cf2dd95 100644
> --- a/block/blk-integrity.c
> +++ b/block/blk-integrity.c
> @@ -420,6 +420,8 @@ int blk_integrity_register(struct gendisk *disk, struct blk_integrity *template)
>  	} else
>  		bi->name = bi_unsupported_name;
>  
> +	queue_require_stable_pages(disk->queue);
> +
>  	return 0;
>  }
>  EXPORT_SYMBOL(blk_integrity_register);
> @@ -438,6 +440,8 @@ void blk_integrity_unregister(struct gendisk *disk)
>  	if (!disk || !disk->integrity)
>  		return;
>  
> +	queue_unrequire_stable_pages(disk->queue);
> +
>  	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..0554f5d 100644
> --- a/include/linux/backing-dev.h
> +++ b/include/linux/backing-dev.h
> @@ -109,6 +109,7 @@ struct backing_dev_info {
>  	struct dentry *debug_dir;
>  	struct dentry *debug_stats;
>  #endif
> +	atomic_t stable_page_users;
>  };
>  
>  int bdi_init(struct backing_dev_info *bdi);
> @@ -307,6 +308,21 @@ 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 void bdi_require_stable_pages(struct backing_dev_info *bdi)
> +{
> +	atomic_inc(&bdi->stable_page_users);
> +}
> +
> +static inline void bdi_unrequire_stable_pages(struct backing_dev_info *bdi)
> +{
> +	atomic_dec(&bdi->stable_page_users);
> +}
> +
> +static inline bool bdi_cap_stable_pages_required(struct backing_dev_info *bdi)
> +{
> +	return atomic_read(&bdi->stable_page_users) > 0;
> +}
> +
>  static inline bool bdi_cap_writeback_dirty(struct backing_dev_info *bdi)
>  {
>  	return !(bdi->capabilities & BDI_CAP_NO_WRITEBACK);
> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index 1756001..bf927c0 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -458,6 +458,16 @@ struct request_queue {
>  				 (1 << QUEUE_FLAG_SAME_COMP)	|	\
>  				 (1 << QUEUE_FLAG_ADD_RANDOM))
>  
> +static inline void queue_require_stable_pages(struct request_queue *q)
> +{
> +	bdi_require_stable_pages(&q->backing_dev_info);
> +}
> +
> +static inline void queue_unrequire_stable_pages(struct request_queue *q)
> +{
> +	bdi_unrequire_stable_pages(&q->backing_dev_info);
> +}
> +
>  static inline void queue_lockdep_assert_held(struct request_queue *q)
>  {
>  	if (q->queue_lock)
> diff --git a/mm/backing-dev.c b/mm/backing-dev.c
> index d3ca2b3..dd9f5ed 100644
> --- a/mm/backing-dev.c
> +++ b/mm/backing-dev.c
> @@ -221,12 +221,48 @@ static ssize_t max_ratio_store(struct device *dev,
>  }
>  BDI_SHOW(max_ratio, bdi->max_ratio)
>  
> +static ssize_t stable_pages_required_store(struct device *dev,
> +					   struct device_attribute *attr,
> +					   const char *buf, size_t count)
> +{
> +	struct backing_dev_info *bdi = dev_get_drvdata(dev);
> +	unsigned int spw;
> +	ssize_t ret;
> +
> +	ret = kstrtouint(buf, 10, &spw);
> +	if (ret < 0)
> +		return ret;
> +
> +	/*
> +	 * SPW could be enabled due to hw requirement, so don't
> +	 * let users disable it.
> +	 */
> +	if (bdi_cap_stable_pages_required(bdi) && spw == 0)
> +		return -EINVAL;
> +
> +	if (spw != 0)
> +		atomic_inc(&bdi->stable_page_users);
> +
> +	return count;
> +}
> +
> +static ssize_t stable_pages_required_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_cap_stable_pages_required(bdi) ? 1 : 0);
> +}
> +
>  #define __ATTR_RW(attr) __ATTR(attr, 0644, attr##_show, attr##_store)
>  
>  static struct device_attribute bdi_dev_attrs[] = {
>  	__ATTR_RW(read_ahead_kb),
>  	__ATTR_RW(min_ratio),
>  	__ATTR_RW(max_ratio),
> +	__ATTR_RW(stable_pages_required),
>  	__ATTR_NULL,
>  };
>  
> @@ -650,6 +686,8 @@ int bdi_init(struct backing_dev_info *bdi)
>  	bdi->write_bandwidth = INIT_BW;
>  	bdi->avg_write_bandwidth = INIT_BW;
>  
> +	atomic_set(&bdi->stable_page_users, 0);
> +
>  	err = fprop_local_init_percpu(&bdi->completions);
>  
>  	if (err) {
> 
> --
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-- 
Jan Kara <jack@xxxxxxx>
SUSE Labs, CR
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