* [PATCH 1/2] btrfs: introduce new device-state read_preferred
2022-07-25 15:10 [PATCH 0/2] btrfs: read_policy type device Anand Jain
@ 2022-07-25 15:10 ` Anand Jain
2022-07-25 15:10 ` [PATCH 2/2] btrfs: introduce new read_policy device Anand Jain
1 sibling, 0 replies; 3+ messages in thread
From: Anand Jain @ 2022-07-25 15:10 UTC (permalink / raw)
To: linux-btrfs; +Cc: Josef Bacik
This is a preparatory patch and introduces a new device flag
'read_preferred', RW-able using sysfs interface.
Signed-off-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
---
fs/btrfs/sysfs.c | 53 ++++++++++++++++++++++++++++++++++++++++++++++
fs/btrfs/volumes.h | 1 +
2 files changed, 54 insertions(+)
diff --git a/fs/btrfs/sysfs.c b/fs/btrfs/sysfs.c
index d5d0717fd09a..ca9812cabece 100644
--- a/fs/btrfs/sysfs.c
+++ b/fs/btrfs/sysfs.c
@@ -1785,6 +1785,58 @@ static ssize_t btrfs_devinfo_error_stats_show(struct kobject *kobj,
}
BTRFS_ATTR(devid, error_stats, btrfs_devinfo_error_stats_show);
+static ssize_t btrfs_devinfo_read_pref_show(struct kobject *kobj,
+ struct kobj_attribute *a, char *buf)
+{
+ int val;
+ struct btrfs_device *device = container_of(kobj, struct btrfs_device,
+ devid_kobj);
+
+ val = !!test_bit(BTRFS_DEV_STATE_READ_PREFERRED, &device->dev_state);
+
+ return snprintf(buf, PAGE_SIZE, "%d\n", val);
+}
+
+static ssize_t btrfs_devinfo_read_pref_store(struct kobject *kobj,
+ struct kobj_attribute *a,
+ const char *buf, size_t len)
+{
+ int ret;
+ unsigned long val;
+ struct btrfs_device *device;
+
+ ret = kstrtoul(skip_spaces(buf), 0, &val);
+ if (ret)
+ return ret;
+
+ if (val != 0 && val != 1)
+ return -EINVAL;
+
+ /*
+ * lock is not required, the btrfs_device struct can't be freed while
+ * its kobject btrfs_device::devid_kobj is still open.
+ */
+ device = container_of(kobj, struct btrfs_device, devid_kobj);
+
+ if (val &&
+ !test_bit(BTRFS_DEV_STATE_READ_PREFERRED, &device->dev_state)) {
+ set_bit(BTRFS_DEV_STATE_READ_PREFERRED, &device->dev_state);
+ btrfs_info(device->fs_devices->fs_info,
+ "set read preferred on devid %llu (%d)",
+ device->devid, task_pid_nr(current));
+ } else if (!val &&
+ test_bit(BTRFS_DEV_STATE_READ_PREFERRED, &device->dev_state)) {
+ clear_bit(BTRFS_DEV_STATE_READ_PREFERRED, &device->dev_state);
+ btrfs_info(device->fs_devices->fs_info,
+ "reset read preferred on devid %llu (%d)",
+ device->devid, task_pid_nr(current));
+ }
+
+ return len;
+}
+BTRFS_ATTR_RW(devid, read_preferred, btrfs_devinfo_read_pref_show,
+ btrfs_devinfo_read_pref_store);
+
/*
* Information about one device.
*
@@ -1798,6 +1850,7 @@ static struct attribute *devid_attrs[] = {
BTRFS_ATTR_PTR(devid, replace_target),
BTRFS_ATTR_PTR(devid, scrub_speed_max),
BTRFS_ATTR_PTR(devid, writeable),
+ BTRFS_ATTR_PTR(devid, read_preferred),
NULL
};
ATTRIBUTE_GROUPS(devid);
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index 5639961b3626..f04a177136b5 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -85,6 +85,7 @@ struct btrfs_io_geometry {
#define BTRFS_DEV_STATE_REPLACE_TGT (3)
#define BTRFS_DEV_STATE_FLUSH_SENT (4)
#define BTRFS_DEV_STATE_NO_READA (5)
+#define BTRFS_DEV_STATE_READ_PREFERRED (6)
struct btrfs_zoned_device_info;
--
2.33.1
^ permalink raw reply related [flat|nested] 3+ messages in thread* [PATCH 2/2] btrfs: introduce new read_policy device
2022-07-25 15:10 [PATCH 0/2] btrfs: read_policy type device Anand Jain
2022-07-25 15:10 ` [PATCH 1/2] btrfs: introduce new device-state read_preferred Anand Jain
@ 2022-07-25 15:10 ` Anand Jain
1 sibling, 0 replies; 3+ messages in thread
From: Anand Jain @ 2022-07-25 15:10 UTC (permalink / raw)
To: linux-btrfs; +Cc: Josef Bacik
Read-policy type 'device' and device flag 'read-preferred':
The read-policy type device picks the device(s) flagged as
read-preferred for reading stripes of type raid1, raid10,
raid1c3 and raid1c4.
A system might contain SSD, nvme, iscsi, or san lun, and which are all
a non-rotational device, so it is not a good idea to set the read-preferred
automatically. Instead, device read-policy along with the read-preferred
flag provides an ability to do it manually. This advanced tuning is useful
in more than one situation, for example,
- In heterogeneous-disk volume, it provides an ability to manually choose
the low latency disks for reading.
- Useful for more accurate testing.
- Avoid known problematic device from reading the chunk until it is
replaced (by marking the other good devices as read-preferred).
Note:
If the read-policy type is set to 'device', but there isn't any device
which is flagged as read-preferred, then stripe 0 is used for reading.
The device replacement won't migrate the read-preferred flag to the new
replace the target device.
As of now, this is an in-memory only feature.
It's pointless to set the read-preferred flag on the missing device, as
IOs aren't submitted to the missing device.
If there is more than one read-preferred device in a chunk, the read IO
shall go to the stripe 0 as of now.
Usage example:
Consider a typical two disks raid1.
Configure devid1 for reading.
$ echo 1 > devinfo/1/read_preferred
$ cat devinfo/1/read_preferred
1
$ cat devinfo/2/read_preferred
0
$ pwd
/sys/fs/btrfs/12345678-1234-1234-1234-123456789abc
$ cat read_policy
[pid] device
$ echo device > ./read_policy
$ cat read_policy
pid [device]
Now read IOs are sent to devid 1 (sdb).
$ echo 3 > /proc/sys/vm/drop_caches
$ md5sum /btrfs/YkZI
$ iostat -zy 1 | egrep 'sdb|sdc' (from another terminal)
sdb 50.00 40048.00 0.00 40048 0
Change the read-preferred device from devid 1 to devid 2 (sdc).
$ echo 0 > ./devinfo/1/read_preferred
[ 3343.918658] BTRFS info (device sdb): reset read preferred on devid 1 (1334)
$ echo 1 > ./devinfo/2/read_preferred
[ 3343.919876] BTRFS info (device sdb): set read preferred on devid 2 (1334)
$ echo 3 > /proc/sys/vm/drop_caches
$ md5sum /btrfs/YkZI
Further read ios are sent to devid 2 (sdc).
$ iostat -zy 1 | egrep 'sdb|sdc' (from another terminal)
sdc 49.00 40048.00 0.00 40048 0
Signed-off-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
---
fs/btrfs/sysfs.c | 2 +-
fs/btrfs/volumes.c | 23 +++++++++++++++++++++++
fs/btrfs/volumes.h | 2 ++
3 files changed, 26 insertions(+), 1 deletion(-)
diff --git a/fs/btrfs/sysfs.c b/fs/btrfs/sysfs.c
index ca9812cabece..7c15fa1a8b33 100644
--- a/fs/btrfs/sysfs.c
+++ b/fs/btrfs/sysfs.c
@@ -1169,7 +1169,7 @@ static bool strmatch(const char *buffer, const char *string)
return false;
}
-static const char * const btrfs_read_policy_name[] = { "pid" };
+static const char * const btrfs_read_policy_name[] = { "pid", "device" };
static ssize_t btrfs_read_policy_show(struct kobject *kobj,
struct kobj_attribute *a, char *buf)
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 272901514b0c..cf358926b52a 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -5793,6 +5793,25 @@ int btrfs_is_parity_mirror(struct btrfs_fs_info *fs_info, u64 logical, u64 len)
return ret;
}
+static int btrfs_find_read_preferred(struct map_lookup *map, int first, int num_stripe)
+{
+ int stripe_index;
+ int last = first + num_stripe;
+
+ /*
+ * If there are more than one read preferred devices, then just pick the
+ * first found read preferred device as of now.
+ */
+ for (stripe_index = first; stripe_index < last; stripe_index++) {
+ if (test_bit(BTRFS_DEV_STATE_READ_PREFERRED,
+ &map->stripes[stripe_index].dev->dev_state))
+ return stripe_index;
+ }
+
+ /* If there is no read preferred device then just use the first stripe */
+ return first;
+}
+
static int find_live_mirror(struct btrfs_fs_info *fs_info,
struct map_lookup *map, int first,
int dev_replace_is_ongoing)
@@ -5822,6 +5841,10 @@ static int find_live_mirror(struct btrfs_fs_info *fs_info,
case BTRFS_READ_POLICY_PID:
preferred_mirror = first + (current->pid % num_stripes);
break;
+ case BTRFS_READ_POLICY_DEVICE:
+ preferred_mirror = btrfs_find_read_preferred(map, first,
+ num_stripes);
+ break;
}
if (dev_replace_is_ongoing &&
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index f04a177136b5..e62252061606 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -260,6 +260,8 @@ enum btrfs_chunk_allocation_policy {
enum btrfs_read_policy {
/* Use process PID to choose the stripe */
BTRFS_READ_POLICY_PID,
+ /* Use the device marked with READ_PREFERRED state */
+ BTRFS_READ_POLICY_DEVICE,
BTRFS_NR_READ_POLICY,
};
--
2.33.1
^ permalink raw reply related [flat|nested] 3+ messages in thread