Re: [PATCH 22/51] writeback: add {CONFIG|BDI_CAP|FS}_CGROUP_WRITEBACK

[Jan Kara]

On Fri 22-05-15 17:13:36, Tejun Heo wrote:
> cgroup writeback requires support from both bdi and filesystem sides.
> Add BDI_CAP_CGROUP_WRITEBACK and FS_CGROUP_WRITEBACK to indicate
> support and enable BDI_CAP_CGROUP_WRITEBACK on block based bdi's by
> default.  Also, define CONFIG_CGROUP_WRITEBACK which is enabled if
> both MEMCG and BLK_CGROUP are enabled.
> 
> inode_cgwb_enabled() which determines whether a given inode's both bdi
> and fs support cgroup writeback is added.
> 
> Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
> Cc: Jens Axboe <axboe@xxxxxxxxx>
> Cc: Jan Kara <jack@xxxxxxx>

Hum, you later changed this to use a per-sb flag instead of a per-fs-type
flag, right? We could do it as well here but OK.

One more question - what does prevent us from supporting CGROUP_WRITEBACK
for all bdis capable of writeback? I guess the reason is that currently
blkcgs are bound to request_queue and we have to have blkcg(s) for
CGROUP_WRITEBACK to work, am I right? But in principle tracking writeback
state and doing writeback per memcg doesn't seem to be bound to any device
properties so we could do that right?

Anyway, this patch looks good. You can add:

Reviewed-by: Jan Kara <jack@xxxxxxxx>

								Honza

> ---
>  block/blk-core.c            |  2 +-
>  include/linux/backing-dev.h | 32 +++++++++++++++++++++++++++++++-
>  include/linux/fs.h          |  1 +
>  init/Kconfig                |  5 +++++
>  4 files changed, 38 insertions(+), 2 deletions(-)
> 
> diff --git a/block/blk-core.c b/block/blk-core.c
> index f46688f..e0f726f 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -620,7 +620,7 @@ struct request_queue *blk_alloc_queue_node(gfp_t gfp_mask, int node_id)
>  
>  	q->backing_dev_info.ra_pages =
>  			(VM_MAX_READAHEAD * 1024) / PAGE_CACHE_SIZE;
> -	q->backing_dev_info.capabilities = 0;
> +	q->backing_dev_info.capabilities = BDI_CAP_CGROUP_WRITEBACK;
>  	q->backing_dev_info.name = "block";
>  	q->node = node_id;
>  
> diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
> index bfdaa18..6bb3123 100644
> --- a/include/linux/backing-dev.h
> +++ b/include/linux/backing-dev.h
> @@ -134,12 +134,15 @@ int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned int max_ratio);
>   * BDI_CAP_NO_WRITEBACK:   Don't write pages back
>   * BDI_CAP_NO_ACCT_WB:     Don't automatically account writeback pages
>   * BDI_CAP_STRICTLIMIT:    Keep number of dirty pages below bdi threshold.
> + *
> + * BDI_CAP_CGROUP_WRITEBACK: Supports cgroup-aware writeback.
>   */
>  #define BDI_CAP_NO_ACCT_DIRTY	0x00000001
>  #define BDI_CAP_NO_WRITEBACK	0x00000002
>  #define BDI_CAP_NO_ACCT_WB	0x00000004
>  #define BDI_CAP_STABLE_WRITES	0x00000008
>  #define BDI_CAP_STRICTLIMIT	0x00000010
> +#define BDI_CAP_CGROUP_WRITEBACK 0x00000020
>  
>  #define BDI_CAP_NO_ACCT_AND_WRITEBACK \
>  	(BDI_CAP_NO_WRITEBACK | BDI_CAP_NO_ACCT_DIRTY | BDI_CAP_NO_ACCT_WB)
> @@ -229,4 +232,31 @@ static inline int bdi_sched_wait(void *word)
>  	return 0;
>  }
>  
> -#endif		/* _LINUX_BACKING_DEV_H */
> +#ifdef CONFIG_CGROUP_WRITEBACK
> +
> +/**
> + * inode_cgwb_enabled - test whether cgroup writeback is enabled on an inode
> + * @inode: inode of interest
> + *
> + * cgroup writeback requires support from both the bdi and filesystem.
> + * Test whether @inode has both.
> + */
> +static inline bool inode_cgwb_enabled(struct inode *inode)
> +{
> +	struct backing_dev_info *bdi = inode_to_bdi(inode);
> +
> +	return bdi_cap_account_dirty(bdi) &&
> +		(bdi->capabilities & BDI_CAP_CGROUP_WRITEBACK) &&
> +		(inode->i_sb->s_type->fs_flags & FS_CGROUP_WRITEBACK);
> +}
> +
> +#else	/* CONFIG_CGROUP_WRITEBACK */
> +
> +static inline bool inode_cgwb_enabled(struct inode *inode)
> +{
> +	return false;
> +}
> +
> +#endif	/* CONFIG_CGROUP_WRITEBACK */
> +
> +#endif	/* _LINUX_BACKING_DEV_H */
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index ce100b87..74e0ae0 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1897,6 +1897,7 @@ struct file_system_type {
>  #define FS_HAS_SUBTYPE		4
>  #define FS_USERNS_MOUNT		8	/* Can be mounted by userns root */
>  #define FS_USERNS_DEV_MOUNT	16 /* A userns mount does not imply MNT_NODEV */
> +#define FS_CGROUP_WRITEBACK	32	/* Supports cgroup-aware writeback */
>  #define FS_RENAME_DOES_D_MOVE	32768	/* FS will handle d_move() during rename() internally. */
>  	struct dentry *(*mount) (struct file_system_type *, int,
>  		       const char *, void *);
> diff --git a/init/Kconfig b/init/Kconfig
> index dc24dec..d4f7633 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -1141,6 +1141,11 @@ config DEBUG_BLK_CGROUP
>  	Enable some debugging help. Currently it exports additional stat
>  	files in a cgroup which can be useful for debugging.
>  
> +config CGROUP_WRITEBACK
> +	bool
> +	depends on MEMCG && BLK_CGROUP
> +	default y
> +
>  endif # CGROUPS
>  
>  config CHECKPOINT_RESTORE
> -- 
> 2.4.0
> 
-- 
Jan Kara <jack@xxxxxxx>
SUSE Labs, CR
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/