On Wed, Jun 26, 2019 at 04:34:02PM +0800, Anand Jain wrote:
> Introduces devid readmirror property, to direct read IO to the specified
> device(s).
>
> The readmirror property is stored as extended attribute on the root
> inode.
So this is permanently stored on the filesystem, is the policy applied
at mount time?
> The readmirror input format is devid1,2,3.. etc. And for the
> each devid provided, a new flag BTRFS_DEV_STATE_READ_OPTIMISED is set.
I'd say it should be called PREFERRED, and the format specifier could
add ":" between devid and the numbers, like "devid:1,2,3", we'll
probably want more types in the future.
This is the first whole-filesystem property so we can't follow a naming
scheme, so we'll have to decide if we go with flat or hierarchical
naming with more generic categories like policy.mirror.read and similar.
> As of now readmirror by devid supports only raid1s. Raid10 support has
> to leverage device grouping feature, which is yet to be implemented.
>
> Signed-off-by: Anand Jain <anand.j...@oracle.com>
> ---
> fs/btrfs/props.c | 69 +++++++++++++++++++++++++++++++++++++++++++++-
> fs/btrfs/volumes.c | 16 +++++++++++
> fs/btrfs/volumes.h | 2 ++
> 3 files changed, 86 insertions(+), 1 deletion(-)
>
> diff --git a/fs/btrfs/props.c b/fs/btrfs/props.c
> index 0dc26a154a98..6a789e1c150c 100644
> --- a/fs/btrfs/props.c
> +++ b/fs/btrfs/props.c
> @@ -316,7 +316,10 @@ static const char *prop_compression_extract(struct inode
> *inode)
> static int prop_readmirror_validate(struct inode *inode, const char *value,
> size_t len)
> {
> + char *value_dup;
> + char *devid_str;
> struct btrfs_root *root = BTRFS_I(inode)->root;
> + struct btrfs_fs_devices *fs_devices = root->fs_info->fs_devices;
>
> if (root->root_key.objectid != BTRFS_FS_TREE_OBJECTID)
> return -EINVAL;
> @@ -324,16 +327,80 @@ static int prop_readmirror_validate(struct inode
> *inode, const char *value,
> if (!len)
> return 0;
>
> - return -EINVAL;
> + if (len <= 5 || strncmp("devid", value, 5))
> + return -EINVAL;
> +
> + value_dup = kstrndup(value + 5, len - 5, GFP_KERNEL);
> + if (!value_dup)
> + return -ENOMEM;
> +
> + while ((devid_str = strsep(&value_dup, ",")) != NULL) {
> + u64 devid;
> + struct btrfs_device *device;
> +
> + if (kstrtoull(devid_str, 10, &devid)) {
> + kfree(value_dup);
> + return -EINVAL;
> + }
> +
> + device = btrfs_find_device(fs_devices, devid, NULL, NULL,
> false);
Doesn't this need locking?
> + if (!device) {
> + kfree(value_dup);
> + return -EINVAL;
> + }
> + }
> +
> + return 0;
> }
>
> static int prop_readmirror_apply(struct inode *inode, const char *value,
> size_t len)
> {
> + char *value_dup;
> + char *devid_str;
> + struct btrfs_device *device;
> struct btrfs_fs_devices *fs_devices = btrfs_sb(inode->i_sb)->fs_devices;
>
> + if (value) {
> + value_dup = kstrndup(value + 5, len - 5, GFP_KERNEL);
> + if (!value_dup)
> + return -ENOMEM;
> + }
> +
> + /* Both set and reset has to clear the exisiting values */
> + list_for_each_entry(device, &fs_devices->devices, dev_list) {
> + if (test_bit(BTRFS_DEV_STATE_READ_OPTIMISED,
> + &device->dev_state)) {
> + clear_bit(BTRFS_DEV_STATE_READ_OPTIMISED,
> + &device->dev_state);
> + }
> + }
And this one too.
> fs_devices->readmirror_policy = BTRFS_READMIRROR_DEFAULT;
>
> + /* Its only reset so just return */
> + if (!value)
> + return 0;
> +
> + while ((devid_str = strsep(&value_dup, ",")) != NULL) {
> + u64 devid;
> +
> + /* Has been verified in validate() this will not fail */
> + if (kstrtoull(devid_str, 10, &devid)) {
> + kfree(value_dup);
> + return -EINVAL;
> + }
> +
> + device = btrfs_find_device(fs_devices, devid, NULL, NULL,
> false);
> + if (!device) {
> + kfree(value_dup);
> + return -EINVAL;
> + }
> +
> + set_bit(BTRFS_DEV_STATE_READ_OPTIMISED, &device->dev_state);
> + fs_devices->readmirror_policy = BTRFS_READMIRROR_DEVID;
> + }
> +
> + kfree(value_dup);
> return 0;
> }
>
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index d72850ed4f88..993645f4b5f6 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -5481,6 +5481,7 @@ static int find_live_mirror(struct btrfs_fs_info
> *fs_info,
> int preferred_mirror;
> int tolerance;
> struct btrfs_device *srcdev;
> + bool found = false;
>
> ASSERT((map->type &
> (BTRFS_BLOCK_GROUP_RAID1_MASK | BTRFS_BLOCK_GROUP_RAID10)));
> @@ -5491,6 +5492,21 @@ static int find_live_mirror(struct btrfs_fs_info
> *fs_info,
> num_stripes = map->num_stripes;
>
> switch(fs_info->fs_devices->readmirror_policy) {
> + case BTRFS_READMIRROR_DEVID:
> + /* skip raid10 for now */
> + if (map->type & BTRFS_BLOCK_GROUP_RAID1) {
> + for (i = first; i < first + num_stripes; i++) {
> + if (test_bit(BTRFS_DEV_STATE_READ_OPTIMISED,
> + &map->stripes[i].dev->dev_state)) {
> + preferred_mirror = i;
> + found = true;
> + break;
> + }
> + }
> + if (found)
> + break;
> + }
> + /* fall through */
> case BTRFS_READMIRROR_DEFAULT:
> /* fall through */
> default:
> diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
> index e985d2133c0a..55b0f3b28595 100644
> --- a/fs/btrfs/volumes.h
> +++ b/fs/btrfs/volumes.h
> @@ -56,6 +56,7 @@ struct btrfs_io_geometry {
> #define BTRFS_DEV_STATE_MISSING (2)
> #define BTRFS_DEV_STATE_REPLACE_TGT (3)
> #define BTRFS_DEV_STATE_FLUSH_SENT (4)
> +#define BTRFS_DEV_STATE_READ_OPTIMISED (5)
>
> struct btrfs_device {
> struct list_head dev_list; /* device_list_mutex */
> @@ -221,6 +222,7 @@ BTRFS_DEVICE_GETSET_FUNCS(bytes_used);
>
> enum btrfs_readmirror_policy {
> BTRFS_READMIRROR_DEFAULT,
> + BTRFS_READMIRROR_DEVID,
> };
>
> struct btrfs_fs_devices {
> --
> 2.20.1 (Apple Git-117)
