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;
};
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;
+ }
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)
--
2.7.0
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