Re: [PATCH 4/4] btrfs: add preferred_metadata mode

Goffredo Baroncelli <kreijack@xxxxxxxxx> · Fri, 29 May 2020 18:26:38 +0200

On 5/29/20 12:02 AM, Hans van Kranenburg wrote:
Hi,

On 5/28/20 8:34 PM, Goffredo Baroncelli wrote:
From: Goffredo Baroncelli <kreijack@xxxxxxxxx>

When this mode is enabled,

The commit message does not mention if this is either only a convenience
during development and testing of the feature to be able to quickly turn
it on/off, or if you intend to have this into the final change set.

Good question. IMHO for the initial devel phase I think that it is useful to have
a preferred_metadata disk (opt-in). Then we could reverse the logic and
default to preferred_metadata. Of course then we will have a
no-preferred_metadata flag (opt-out)

the allocation policy of the chunk
is so modified:
- allocation of metadata chunk: priority is given to preferred_metadata
   disks.
- allocation of data chunk: priority is given to a non preferred_metadata
   disk.

When a striped profile is involved (like RAID0,5,6), the logic
is a bit more complex. If there are enough disks, the data profiles
are stored on the non preferred_metadata disks; instead the metadata
profiles are stored on the preferred_metadata disk.
If the disks are not enough, then the profile is allocated on all
the disks.

Example: assuming that sda, sdb, sdc are ssd disks, and sde, sdf are
non preferred_metadata ones.
A data profile raid6, will be stored on sda, sdb, sdc, sde, sdf (sde
and sdf are not enough to host a raid5 profile).
A metadata profile raid6, will be stored on sda, sdb, sdc (these
are enough to host a raid6 profile).

To enable this mode pass -o dedicated_metadata at mount time.

Is it dedicated_metadata or preferred_metadata?

It was an copy&paste error. It should be preferred_metadata

Signed-off-by: Goffredo Baroncelli <kreijack@xxxxxxxxx>
---
  fs/btrfs/ctree.h   |  1 +
  fs/btrfs/super.c   |  8 +++++
  fs/btrfs/volumes.c | 89 ++++++++++++++++++++++++++++++++++++++++++++--
  fs/btrfs/volumes.h |  1 +
  4 files changed, 97 insertions(+), 2 deletions(-)

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 03ea7370aea7..779760fd27b1 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1239,6 +1239,7 @@ static inline u32 BTRFS_MAX_XATTR_SIZE(const struct btrfs_fs_info *info)
  #define BTRFS_MOUNT_NOLOGREPLAY		(1 << 27)
  #define BTRFS_MOUNT_REF_VERIFY		(1 << 28)
  #define BTRFS_MOUNT_DISCARD_ASYNC	(1 << 29)
+#define BTRFS_MOUNT_PREFERRED_METADATA	(1 << 30)
  
  #define BTRFS_DEFAULT_COMMIT_INTERVAL	(30)
  #define BTRFS_DEFAULT_MAX_INLINE	(2048)
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 438ecba26557..80700dc9dcf8 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -359,6 +359,7 @@ enum {
  #ifdef CONFIG_BTRFS_FS_REF_VERIFY
  	Opt_ref_verify,
  #endif
+	Opt_preferred_metadata,
  	Opt_err,
  };
  
@@ -430,6 +431,7 @@ static const match_table_t tokens = {
  #ifdef CONFIG_BTRFS_FS_REF_VERIFY
  	{Opt_ref_verify, "ref_verify"},
  #endif
+	{Opt_preferred_metadata, "preferred_metadata"},
  	{Opt_err, NULL},
  };
  
@@ -881,6 +883,10 @@ int btrfs_parse_options(struct btrfs_fs_info *info, char *options,
  			btrfs_set_opt(info->mount_opt, REF_VERIFY);
  			break;
  #endif
+		case Opt_preferred_metadata:
+			btrfs_set_and_info(info, PREFERRED_METADATA,
+					"enabling preferred_metadata");
+			break;
  		case Opt_err:
  			btrfs_err(info, "unrecognized mount option '%s'", p);
  			ret = -EINVAL;
@@ -1403,6 +1409,8 @@ static int btrfs_show_options(struct seq_file *seq, struct dentry *dentry)
  #endif
  	if (btrfs_test_opt(info, REF_VERIFY))
  		seq_puts(seq, ",ref_verify");
+	if (btrfs_test_opt(info, PREFERRED_METADATA))
+		seq_puts(seq, ",preferred_metadata");
  	seq_printf(seq, ",subvolid=%llu",
  		  BTRFS_I(d_inode(dentry))->root->root_key.objectid);
  	seq_puts(seq, ",subvol=");
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 5265f54c2931..c68efb15e473 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -4770,6 +4770,56 @@ static int btrfs_cmp_device_info(const void *a, const void *b)
  	return 0;
  }
  
+/*
+ * sort the devices in descending order by preferred_metadata,
+ * max_avail, total_avail
+ */
+static int btrfs_cmp_device_info_metadata(const void *a, const void *b)
+{
+	const struct btrfs_device_info *di_a = a;
+	const struct btrfs_device_info *di_b = b;
+
+	/* metadata -> preferred_metadata first */
+	if (di_a->preferred_metadata && !di_b->preferred_metadata)
+		return -1;
+	if (!di_a->preferred_metadata && di_b->preferred_metadata)
+		return 1;
+	if (di_a->max_avail > di_b->max_avail)
+		return -1;
+	if (di_a->max_avail < di_b->max_avail)
+		return 1;
+	if (di_a->total_avail > di_b->total_avail)
+		return -1;
+	if (di_a->total_avail < di_b->total_avail)
+		return 1;
+	return 0;
+}
+
+/*
+ * sort the devices in descending order by !preferred_metadata,
+ * max_avail, total_avail
+ */
+static int btrfs_cmp_device_info_data(const void *a, const void *b)
+{
+	const struct btrfs_device_info *di_a = a;
+	const struct btrfs_device_info *di_b = b;
+
+	/* data -> preferred_metadata last */
+	if (di_a->preferred_metadata && !di_b->preferred_metadata)
+		return 1;
+	if (!di_a->preferred_metadata && di_b->preferred_metadata)
+		return -1;
+	if (di_a->max_avail > di_b->max_avail)
+		return -1;
+	if (di_a->max_avail < di_b->max_avail)
+		return 1;
+	if (di_a->total_avail > di_b->total_avail)
+		return -1;
+	if (di_a->total_avail < di_b->total_avail)
+		return 1;
+	return 0;
+}
+
  static void check_raid56_incompat_flag(struct btrfs_fs_info *info, u64 type)
  {
  	if (!(type & BTRFS_BLOCK_GROUP_RAID56_MASK))
@@ -4885,6 +4935,7 @@ static int gather_device_info(struct btrfs_fs_devices *fs_devices,
  	int ndevs = 0;
  	u64 max_avail;
  	u64 dev_offset;
+	int nr_preferred_metadata = 0;
  
  	/*
  	 * in the first pass through the devices list, we gather information
@@ -4937,15 +4988,49 @@ static int gather_device_info(struct btrfs_fs_devices *fs_devices,
  		devices_info[ndevs].max_avail = max_avail;
  		devices_info[ndevs].total_avail = total_avail;
  		devices_info[ndevs].dev = device;
+		devices_info[ndevs].preferred_metadata = !!(device->type &
+			BTRFS_DEV_PREFERRED_METADATA);
+		if (devices_info[ndevs].preferred_metadata)
+			nr_preferred_metadata++;
  		++ndevs;
  	}
  	ctl->ndevs = ndevs;
  
+	BUG_ON(nr_preferred_metadata > ndevs);
  	/*
  	 * now sort the devices by hole size / available space
  	 */
-	sort(devices_info, ndevs, sizeof(struct btrfs_device_info),
-	     btrfs_cmp_device_info, NULL);
+	if (((ctl->type & BTRFS_BLOCK_GROUP_DATA) &&
+	     (ctl->type & BTRFS_BLOCK_GROUP_METADATA)) ||
+	    !btrfs_test_opt(info, PREFERRED_METADATA)) {
+		/* mixed bg or PREFERRED_METADATA not set */
+		sort(devices_info, ctl->ndevs, sizeof(struct btrfs_device_info),
+			     btrfs_cmp_device_info, NULL);
+	} else {
+		/*
+		 * if PREFERRED_METADATA is set, sort the device considering
+		 * also the kind (preferred_metadata or not). Limit the
+		 * availables devices to the ones of the same kind, to avoid
+		 * that a striped profile, like raid5, spreads to all kind of
+		 * devices.
+		 * It is allowed to use different kinds of devices if the ones
+		 * of the same kind are not enough alone.
+		 */
+		if (ctl->type & BTRFS_BLOCK_GROUP_DATA) {
+			int nr_data = ctl->ndevs - nr_preferred_metadata;
+			sort(devices_info, ctl->ndevs,
+				     sizeof(struct btrfs_device_info),
+				     btrfs_cmp_device_info_data, NULL);
+			if (nr_data >= ctl->devs_min)
+				ctl->ndevs = nr_data;
+		} else { /* non data -> metadata and system */
+			sort(devices_info, ctl->ndevs,
+				     sizeof(struct btrfs_device_info),
+				     btrfs_cmp_device_info_metadata, NULL);
+			if (nr_preferred_metadata >= ctl->devs_min)
+				ctl->ndevs = nr_preferred_metadata;
+		}
+	}
  
  	return 0;
  }
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index 0ac5bf2b95e6..d39c3b0e7569 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -347,6 +347,7 @@ struct btrfs_device_info {
  	u64 dev_offset;
  	u64 max_avail;
  	u64 total_avail;
+	int preferred_metadata:1;
  };
  
  struct btrfs_raid_attr {




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