As of now we use %pid method to read stripped mirrored data. So
application's process id determines the stripe id to be read. This type
of routing typically helps in a system with many small independent
applications tying to read random data. On the other hand the %pid
based read IO distribution policy is inefficient if there is a single
application trying to read large data and the overall disk bandwidth
remains under utilized.
So this patch introduces a framework where we could add more readmirror
policies, such as routing the IO based on device's waitqueue or manual
when we have a read-preferred device or a policy based on the target
storage caching.
Signed-off-by: Anand Jain <anand.jain@xxxxxxxxxx>
---
fs/btrfs/volumes.c | 16 +++++++++++++++-
fs/btrfs/volumes.h | 8 ++++++++
2 files changed, 23 insertions(+), 1 deletion(-)
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index c95e47aa84f8..0c6caae29248 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -1162,6 +1162,8 @@ static int open_fs_devices(struct btrfs_fs_devices *fs_devices,
fs_devices->opened = 1;
fs_devices->latest_bdev = latest_dev->bdev;
fs_devices->total_rw_bytes = 0;
+ /* Set the default readmirror policy */
+ atomic_set(&fs_devices->readmirror, BTRFS_READMIRROR_DEFAULT);
out:
return ret;
}
@@ -5300,7 +5302,19 @@ static int find_live_mirror(struct btrfs_fs_info *fs_info,
else
num_stripes = map->num_stripes;
- preferred_mirror = first + current->pid % num_stripes;
+ switch (atomic_read(&fs_info->fs_devices->readmirror)) {
+ case BTRFS_READMIRROR_BY_PID:
+ preferred_mirror = first + current->pid % num_stripes;
+ break;
+ default:
+ /*
+ * Shouln't happen, just warn and use default instead of failing.
+ */
+ btrfs_warn_rl(fs_info,
+ "unknown readmirror type %u, fallback to by_pid",
+ atomic_read(&fs_info->fs_devices->readmirror));
+ preferred_mirror = first + current->pid % num_stripes;
+ }
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 68021d1ee216..d9c4c4e1dbc2 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -209,6 +209,12 @@ struct btrfs_device {
BTRFS_DEVICE_GETSET_FUNCS(disk_total_bytes);
BTRFS_DEVICE_GETSET_FUNCS(bytes_used);
+/* readmirror_policy types */
+#define BTRFS_READMIRROR_DEFAULT BTRFS_READMIRROR_BY_PID
+enum btrfs_readmirror_policy_type {
+ BTRFS_READMIRROR_BY_PID,
+};
+
struct btrfs_fs_devices {
u8 fsid[BTRFS_FSID_SIZE]; /* FS specific uuid */
u8 metadata_uuid[BTRFS_FSID_SIZE];
@@ -260,6 +266,8 @@ struct btrfs_fs_devices {
struct kobject *devices_kobj;
struct kobject *devinfo_kobj;
struct completion kobj_unregister;
+
+ atomic_t readmirror;
};
#define BTRFS_BIO_INLINE_CSUM_SIZE 64
--
1.8.3.1
