On 30.01.2018 08:30, Anand Jain wrote:
> In case of RAID1 and RAID10 devices are mirror-ed, a read IO can
> pick any device for reading. This choice of picking a device for
> reading should be configurable. In short not one policy would
> satisfy all types of workload and configs.
>
> So before we add more policies, this patch-set makes existing
> $pid policy configurable from the mount option.
>
> For example..
> mount -o read_mirror_policy=pid (which is also default)
>
> Signed-off-by: Anand Jain <anand.j...@oracle.com>
> ---
> fs/btrfs/ctree.h | 2 ++
> fs/btrfs/super.c | 10 ++++++++++
> fs/btrfs/volumes.c | 8 +++++++-
> fs/btrfs/volumes.h | 5 +++++
> 4 files changed, 24 insertions(+), 1 deletion(-)
>
> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
> index 1a462ab85c49..4759e988b0df 100644
> --- a/fs/btrfs/ctree.h
> +++ b/fs/btrfs/ctree.h
> @@ -1100,6 +1100,8 @@ struct btrfs_fs_info {
> spinlock_t ref_verify_lock;
> struct rb_root block_tree;
> #endif
> + /* Policy to balance read across mirrored devices */
> + int read_mirror_policy;
make that member enum btrfs_read_mirror_type
> };
>
> static inline struct btrfs_fs_info *btrfs_sb(struct super_block *sb)
> diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
> index 367ecbf477b9..dfe6b3c67df3 100644
> --- a/fs/btrfs/super.c
> +++ b/fs/btrfs/super.c
> @@ -329,6 +329,7 @@ enum {
> #ifdef CONFIG_BTRFS_FS_REF_VERIFY
> Opt_ref_verify,
> #endif
> + Opt_read_mirror_policy,
> Opt_err,
> };
>
> @@ -393,6 +394,7 @@ static const match_table_t tokens = {
> #ifdef CONFIG_BTRFS_FS_REF_VERIFY
> {Opt_ref_verify, "ref_verify"},
> #endif
> + {Opt_read_mirror_policy, "read_mirror_policy=%s"},
> {Opt_err, NULL},
> };
>
> @@ -839,6 +841,14 @@ int btrfs_parse_options(struct btrfs_fs_info *info, char
> *options,
> btrfs_set_opt(info->mount_opt, REF_VERIFY);
> break;
> #endif
> + case Opt_read_mirror_policy:
> + if (strcmp(args[0].from, "pid") == 0) {
> + info->read_mirror_policy =
> + BTRFS_READ_MIRROR_BY_PID;
> + break;
> + }
> + ret = -EINVAL;
> + goto out;
> case Opt_err:
> btrfs_info(info, "unrecognized mount option '%s'", p);
> ret = -EINVAL;
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index a61715677b67..39ba59832f38 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -5269,7 +5269,13 @@ static int find_live_mirror(struct btrfs_fs_info
> *fs_info,
> else
> num = map->num_stripes;
>
> - optimal = first + current->pid % num;
> + switch(fs_info->read_mirror_policy) {
> + case BTRFS_READ_MIRROR_DEFAULT:
> + case BTRFS_READ_MIRROR_BY_PID:
> + default:
> + optimal = first + current->pid % num;
> + break;
> + }
Why not factor out this code in a separate function with descriptive
name and some documentation. It seems you have plans how to extend this
mechanism further so let's try and make it maintainable from the get-go.
>
> if (dev_replace_is_ongoing &&
> fs_info->dev_replace.cont_reading_from_srcdev_mode ==
> diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
> index 28c28eeadff3..78f35d299a61 100644
> --- a/fs/btrfs/volumes.h
> +++ b/fs/btrfs/volumes.h
> @@ -47,6 +47,11 @@ struct btrfs_pending_bios {
> #define btrfs_device_data_ordered_init(device) do { } while (0)
> #endif
>
> +enum btrfs_read_mirror_type {
> + BTRFS_READ_MIRROR_DEFAULT,
> + BTRFS_READ_MIRROR_BY_PID,
> +};
> +
> #define BTRFS_DEV_STATE_WRITEABLE (0)
> #define BTRFS_DEV_STATE_IN_FS_METADATA (1)
> #define BTRFS_DEV_STATE_MISSING (2)
>
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