On 1/2/20 5:12 AM, Anand Jain wrote:
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 read IO 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 wait-queue 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> --- v2: Declare fs_devices::readmirror as u8 instead of atomic_t A small change in comment and change log wordings. 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..e26af766f2b9 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 */ + 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 (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 by_pid instead of failing. + */ + btrfs_warn_rl(fs_info, + "unknown readmirror type %u, fallback to by_pid", + 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..f5f091f3c72b 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; + + u8 readmirror;
The only valid values for this are the enum, so make this enum btrfs_readmirror_policy_type readmirror; Thanks, Josef
