On Wed, Jun 26, 2019 at 04:34:01PM +0800, Anand Jain wrote:
> Function call chain __btrfs_map_block()->find_live_mirror() uses
> thread %pid to determine the %mirror_num for the read when mirror_num=0
> in the argument.
>
> This patch introduces a framework so that readmirror is a configurable
> parameter, with default set to pid.
>
> Signed-off-by: Anand Jain <anand.j...@oracle.com>
> ---
> fs/btrfs/props.c | 41 +++++++++++++++++++++++++++++++++++++++++
> fs/btrfs/volumes.c | 9 ++++++++-
> fs/btrfs/volumes.h | 6 ++++++
> 3 files changed, 55 insertions(+), 1 deletion(-)
>
> diff --git a/fs/btrfs/props.c b/fs/btrfs/props.c
> index f9143f7c006d..0dc26a154a98 100644
> --- a/fs/btrfs/props.c
> +++ b/fs/btrfs/props.c
> @@ -10,6 +10,7 @@
> #include "ctree.h"
> #include "xattr.h"
> #include "compression.h"
> +#include "volumes.h"
>
> #define BTRFS_PROP_HANDLERS_HT_BITS 8
> static DEFINE_HASHTABLE(prop_handlers_ht, BTRFS_PROP_HANDLERS_HT_BITS);
> @@ -312,6 +313,39 @@ static const char *prop_compression_extract(struct inode
> *inode)
> return NULL;
> }
>
> +static int prop_readmirror_validate(struct inode *inode, const char *value,
> + size_t len)
> +{
> + struct btrfs_root *root = BTRFS_I(inode)->root;
> +
> + if (root->root_key.objectid != BTRFS_FS_TREE_OBJECTID)
> + return -EINVAL;
> +
> + if (!len)
> + return 0;
> +
> + return -EINVAL;
> +}
> +
> +static int prop_readmirror_apply(struct inode *inode, const char *value,
> + size_t len)
> +{
> + struct btrfs_fs_devices *fs_devices = btrfs_sb(inode->i_sb)->fs_devices;
> +
> + fs_devices->readmirror_policy = BTRFS_READMIRROR_DEFAULT;
> +
> + return 0;
> +}
> +
> +static const char *prop_readmirror_extract(struct inode *inode)
> +{
> + /*
> + * readmirror policy is applied for the whole FS, inheritance is not
> + * applicable.
> + */
Extract is the 'get' implementation of the property, not inheritance, or
I don't understand what does the comment refer to.
> + return NULL;
The return value should reflect the status of the property, ie.
basically the same value that would set the current state.
> +}
> +
> static struct prop_handler prop_handlers[] = {
> {
> .xattr_name = XATTR_BTRFS_PREFIX "compression",
> @@ -320,6 +354,13 @@ static struct prop_handler prop_handlers[] = {
> .extract = prop_compression_extract,
> .inheritable = 1
> },
> + {
> + .xattr_name = XATTR_BTRFS_PREFIX "readmirror",
> + .validate = prop_readmirror_validate,
> + .apply = prop_readmirror_apply,
> + .extract = prop_readmirror_extract,
> + .inheritable = 0
> + },
> };
>
> static int inherit_props(struct btrfs_trans_handle *trans,
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index a13ddba1ebc3..d72850ed4f88 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -5490,7 +5490,14 @@ 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_policy) {
> + case BTRFS_READMIRROR_DEFAULT:
> + /* fall through */
> + default:
> + /* readmirror as per thread pid */
> + preferred_mirror = first + current->pid % num_stripes;
> + 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 7f6aa1816409..e985d2133c0a 100644
> --- a/fs/btrfs/volumes.h
> +++ b/fs/btrfs/volumes.h
> @@ -219,6 +219,10 @@ BTRFS_DEVICE_GETSET_FUNCS(total_bytes);
> BTRFS_DEVICE_GETSET_FUNCS(disk_total_bytes);
> BTRFS_DEVICE_GETSET_FUNCS(bytes_used);
>
> +enum btrfs_readmirror_policy {
> + BTRFS_READMIRROR_DEFAULT,
> +};
> +
> struct btrfs_fs_devices {
> u8 fsid[BTRFS_FSID_SIZE]; /* FS specific uuid */
> u8 metadata_uuid[BTRFS_FSID_SIZE];
> @@ -269,6 +273,8 @@ struct btrfs_fs_devices {
> struct kobject fsid_kobj;
> struct kobject *device_dir_kobj;
> struct completion kobj_unregister;
> +
> + int readmirror_policy;
> };
>
> #define BTRFS_BIO_INLINE_CSUM_SIZE 64
> --
> 2.20.1 (Apple Git-117)
