[PATCH] btrfs: sysfs: set / query btrfs stripe size

[Stefan Roesch <shr@fb.com>]

Motivation:
The btrfs allocator is currently not ideal for all workloads. It tends
to suffer from overallocating data block groups and underallocating
metadata block groups. This results in filesystems becoming read-only
even though there is plenty of "free" space.
This is naturally confusing and distressing to users.

Changes:
  - Increase the default chunk size allocation for metadata to 5GB
    for devices with > 50GB storage space.

  - Add a new sysfs setting to control the stripe size
      /sys/fs/btrfs/<UUID>/allocation/<block_type>/stripe_size

  - For testing add a new sysfs setting to force a chunk allocation.
    This setting is only available if the kernel is compiled with
    CONFIG_BTRFS_DEBUG.
      /sys/fs/btrfs/<UUID>/allocation/<block_type>/force_chunk_alloc

Testing:
  A new test is being added to the xfstest suite. For reference the
  corresponding patch has the title:
    [PATCH] btrfs: Test chunk allocation with different sizes

  In addition also manual testing has been performed.
    - Run xfstests with the changes and the new test. It does not
      show new diffs.
    - Test with storage devices 10G, 20G, 30G, 50G, 60G
      - Default allocation
      - Increase of chunk size
      - If the stripe size is > the free space, it allocates
        free space - 1MB. The 1MB is left as free space.
      - If the device has a storage size > 50G, it uses a 5GB
        chunk size for new allocations.

Signed-off-by: Stefan Roesch <shr@fb.com>
---
 fs/btrfs/space-info.c |  52 +++++++++++++++
 fs/btrfs/space-info.h |   4 ++
 fs/btrfs/sysfs.c      | 145 ++++++++++++++++++++++++++++++++++++++++++
 fs/btrfs/volumes.c    |  30 ++++-----
 4 files changed, 212 insertions(+), 19 deletions(-)

diff --git a/fs/btrfs/space-info.c b/fs/btrfs/space-info.c
index 48d77f360a24..e082654c85f1 100644
--- a/fs/btrfs/space-info.c
+++ b/fs/btrfs/space-info.c
@@ -181,6 +181,54 @@ void btrfs_clear_space_info_full(struct btrfs_fs_info *info)
 		found->full = 0;
 }
 
+/*
+ * Compute stripe size depending on block type.
+ */
+static u64 compute_stripe_size(struct btrfs_fs_info *info, u64 flags)
+{
+	if (flags & BTRFS_BLOCK_GROUP_DATA) {
+		return SZ_1G;
+	} else if (flags & BTRFS_BLOCK_GROUP_METADATA) {
+		/* For larger filesystems, use larger metadata chunks */
+		return info->fs_devices->total_rw_bytes > 50ULL * SZ_1G
+			? 5ULL * SZ_1G
+			: SZ_256M;
+	} else if (flags & BTRFS_BLOCK_GROUP_SYSTEM) {
+		return SZ_32M;
+	}
+
+	BUG();
+}
+
+/*
+ * Compute chunk size depending on block type and stripe size.
+ */
+static u64 compute_chunk_size(u64 flags, u64 max_stripe_size)
+{
+	if (flags & BTRFS_BLOCK_GROUP_DATA)
+		return BTRFS_MAX_DATA_CHUNK_SIZE;
+	else if (flags & BTRFS_BLOCK_GROUP_METADATA)
+		return max_stripe_size;
+	else if (flags & BTRFS_BLOCK_GROUP_SYSTEM)
+		return 2 * max_stripe_size;
+
+	BUG();
+}
+
+/*
+ * Update maximum stripe size and chunk size.
+ *
+ */
+void btrfs_update_space_info_max_alloc_sizes(struct btrfs_space_info *space_info,
+					     u64 flags, u64 max_stripe_size)
+{
+	spin_lock(&space_info->lock);
+	space_info->max_stripe_size = max_stripe_size;
+	space_info->max_chunk_size = compute_chunk_size(flags,
+						space_info->max_stripe_size);
+	spin_unlock(&space_info->lock);
+}
+
 static int create_space_info(struct btrfs_fs_info *info, u64 flags)
 {
 
@@ -203,6 +251,10 @@ static int create_space_info(struct btrfs_fs_info *info, u64 flags)
 	INIT_LIST_HEAD(&space_info->priority_tickets);
 	space_info->clamp = 1;
 
+	space_info->max_stripe_size = compute_stripe_size(info, flags);
+	space_info->max_chunk_size = compute_chunk_size(flags,
+						space_info->max_stripe_size);
+
 	ret = btrfs_sysfs_add_space_info_type(info, space_info);
 	if (ret)
 		return ret;
diff --git a/fs/btrfs/space-info.h b/fs/btrfs/space-info.h
index cb5056472e79..5ee3e381de38 100644
--- a/fs/btrfs/space-info.h
+++ b/fs/btrfs/space-info.h
@@ -23,6 +23,8 @@ struct btrfs_space_info {
 	u64 max_extent_size;	/* This will hold the maximum extent size of
 				   the space info if we had an ENOSPC in the
 				   allocator. */
+	u64 max_chunk_size; /* maximum chunk size in bytes */
+	u64 max_stripe_size; /* maximum stripe size in bytes */
 
 	int clamp;		/* Used to scale our threshold for preemptive
 				   flushing. The value is >> clamp, so turns
@@ -115,6 +117,8 @@ void btrfs_update_space_info(struct btrfs_fs_info *info, u64 flags,
 			     u64 total_bytes, u64 bytes_used,
 			     u64 bytes_readonly, u64 bytes_zone_unusable,
 			     struct btrfs_space_info **space_info);
+void btrfs_update_space_info_max_alloc_sizes(struct btrfs_space_info *space_info,
+			     u64 flags, u64 max_stripe_size);
 struct btrfs_space_info *btrfs_find_space_info(struct btrfs_fs_info *info,
 					       u64 flags);
 u64 __pure btrfs_space_info_used(struct btrfs_space_info *s_info,
diff --git a/fs/btrfs/sysfs.c b/fs/btrfs/sysfs.c
index 25a6f587852b..df3913027df9 100644
--- a/fs/btrfs/sysfs.c
+++ b/fs/btrfs/sysfs.c
@@ -21,6 +21,7 @@
 #include "space-info.h"
 #include "block-group.h"
 #include "qgroup.h"
+#include "misc.h"
 
 /*
  * Structure name                       Path
@@ -92,6 +93,7 @@ static struct btrfs_feature_attr btrfs_attr_features_##_name = {	     \
 
 static inline struct btrfs_fs_info *to_fs_info(struct kobject *kobj);
 static inline struct btrfs_fs_devices *to_fs_devs(struct kobject *kobj);
+static inline struct kobject *get_btrfs_kobj(struct kobject *kobj);
 
 static struct btrfs_feature_attr *to_btrfs_feature_attr(struct kobj_attribute *a)
 {
@@ -709,6 +711,125 @@ static ssize_t btrfs_space_info_show_##field(struct kobject *kobj,	\
 }									\
 BTRFS_ATTR(space_info, field, btrfs_space_info_show_##field)
 
+/*
+ * Return space info stripe size.
+ */
+static ssize_t btrfs_stripe_size_show(struct kobject *kobj,
+				      struct kobj_attribute *a, char *buf)
+{
+	struct btrfs_space_info *sinfo = to_space_info(kobj);
+
+	return btrfs_show_u64(&sinfo->max_stripe_size, &sinfo->lock, buf);
+}
+
+/*
+ * Store new user supplied stripe size in space info.
+ *
+ * Note: If the new stripe size value is larger than 10% of free space it is
+ *       reduced to match that limit.
+ */
+static ssize_t btrfs_stripe_size_store(struct kobject *kobj,
+				       struct kobj_attribute *a,
+				       const char *buf, size_t len)
+{
+	struct btrfs_space_info *space_info = to_space_info(kobj);
+	struct btrfs_fs_info *fs_info = to_fs_info(get_btrfs_kobj(kobj));
+	u64 val;
+	int ret;
+
+	if (!capable(CAP_SYS_ADMIN))
+		return -EPERM;
+
+	if (!fs_info) {
+		pr_err("couldn't get fs_info\n");
+		return -EPERM;
+	}
+
+	if (sb_rdonly(fs_info->sb))
+		return -EROFS;
+
+	if (!fs_info->fs_devices)
+		return -EINVAL;
+
+	if (fs_info->fs_devices->chunk_alloc_policy == BTRFS_CHUNK_ALLOC_ZONED)
+		return -EINVAL;
+
+	if (!space_info) {
+		btrfs_err(fs_info, "couldn't get space_info\n");
+		return -EPERM;
+	}
+
+	ret = kstrtoull(buf, 10, &val);
+	if (ret)
+		return ret;
+
+	/*
+	 * Limit stripe size to 10% of available space.
+	 */
+	val = min(div_factor(fs_info->fs_devices->total_rw_bytes, 1), val);
+	btrfs_update_space_info_max_alloc_sizes(space_info, space_info->flags, val);
+
+	return val;
+}
+
+#ifdef CONFIG_BTRFS_DEBUG
+/*
+ * Return if space info force allocation chunk flag is set.
+ */
+static ssize_t btrfs_force_chunk_alloc_show(struct kobject *kobj,
+					    struct kobj_attribute *a,
+					    char *buf)
+{
+	return snprintf(buf, PAGE_SIZE, "0\n");
+}
+
+/*
+ * Request chunk allocation with current chunk size.
+ */
+static ssize_t btrfs_force_chunk_alloc_store(struct kobject *kobj,
+					     struct kobj_attribute *a,
+					     const char *buf, size_t len)
+{
+	struct btrfs_space_info *space_info = to_space_info(kobj);
+	struct btrfs_fs_info *fs_info = to_fs_info(get_btrfs_kobj(kobj));
+	struct btrfs_trans_handle *trans;
+	unsigned long val;
+	int ret;
+
+	if (!fs_info) {
+		pr_err("couldn't get fs_info\n");
+		return -EPERM;
+	}
+
+	if (!capable(CAP_SYS_ADMIN))
+		return -EPERM;
+
+	if (sb_rdonly(fs_info->sb))
+		return -EROFS;
+
+	ret = kstrtoul(buf, 10, &val);
+	if (ret)
+		return ret;
+
+	if (val == 0)
+		return -EINVAL;
+
+	/*
+	 * Allocate new chunk.
+	 */
+	trans = btrfs_start_transaction(fs_info->extent_root, 0);
+	if (!trans)
+		return PTR_ERR(trans);
+	ret = btrfs_force_chunk_alloc(trans, space_info->flags);
+	btrfs_end_transaction(trans);
+
+	if (ret == 1)
+		return len;
+
+	return -ENOSPC;
+}
+#endif
+
 SPACE_INFO_ATTR(flags);
 SPACE_INFO_ATTR(total_bytes);
 SPACE_INFO_ATTR(bytes_used);
@@ -719,6 +840,12 @@ SPACE_INFO_ATTR(bytes_readonly);
 SPACE_INFO_ATTR(bytes_zone_unusable);
 SPACE_INFO_ATTR(disk_used);
 SPACE_INFO_ATTR(disk_total);
+BTRFS_ATTR_RW(space_info, stripe_size, btrfs_stripe_size_show,
+	      btrfs_stripe_size_store);
+#ifdef CONFIG_BTRFS_DEBUG
+BTRFS_ATTR_RW(space_info, force_chunk_alloc, btrfs_force_chunk_alloc_show,
+	      btrfs_force_chunk_alloc_store);
+#endif
 
 /*
  * Allocation information about block group types.
@@ -736,6 +863,10 @@ static struct attribute *space_info_attrs[] = {
 	BTRFS_ATTR_PTR(space_info, bytes_zone_unusable),
 	BTRFS_ATTR_PTR(space_info, disk_used),
 	BTRFS_ATTR_PTR(space_info, disk_total),
+	BTRFS_ATTR_PTR(space_info, stripe_size),
+#ifdef CONFIG_BTRFS_DEBUG
+	BTRFS_ATTR_PTR(space_info, force_chunk_alloc),
+#endif
 	NULL,
 };
 ATTRIBUTE_GROUPS(space_info);
@@ -1103,6 +1234,20 @@ static inline struct btrfs_fs_info *to_fs_info(struct kobject *kobj)
 	return to_fs_devs(kobj)->fs_info;
 }
 
+/*
+ * Get btrfs sysfs kobject.
+ */
+static inline struct kobject *get_btrfs_kobj(struct kobject *kobj)
+{
+	while (kobj) {
+		if (kobj->ktype == &btrfs_ktype)
+			return kobj;
+		kobj = kobj->parent;
+	}
+
+	return NULL;
+}
+
 #define NUM_FEATURE_BITS 64
 #define BTRFS_FEATURE_NAME_MAX 13
 static char btrfs_unknown_feature_names[FEAT_MAX][NUM_FEATURE_BITS][BTRFS_FEATURE_NAME_MAX];
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 6031e2f4c6bc..4ab581c03cda 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -4990,7 +4990,9 @@ struct alloc_chunk_ctl {
 	int ncopies;
 	/* Number of stripes worth of bytes to store parity information */
 	int nparity;
+	/* Maximum stripe size */
 	u64 max_stripe_size;
+	/* Maximum chunk size */
 	u64 max_chunk_size;
 	u64 dev_extent_min;
 	u64 stripe_size;
@@ -5002,26 +5004,16 @@ static void init_alloc_chunk_ctl_policy_regular(
 				struct btrfs_fs_devices *fs_devices,
 				struct alloc_chunk_ctl *ctl)
 {
-	u64 type = ctl->type;
+	struct btrfs_space_info *space_info;
 
-	if (type & BTRFS_BLOCK_GROUP_DATA) {
-		ctl->max_stripe_size = SZ_1G;
-		ctl->max_chunk_size = BTRFS_MAX_DATA_CHUNK_SIZE;
-	} else if (type & BTRFS_BLOCK_GROUP_METADATA) {
-		/* For larger filesystems, use larger metadata chunks */
-		if (fs_devices->total_rw_bytes > 50ULL * SZ_1G)
-			ctl->max_stripe_size = SZ_1G;
-		else
-			ctl->max_stripe_size = SZ_256M;
-		ctl->max_chunk_size = ctl->max_stripe_size;
-	} else if (type & BTRFS_BLOCK_GROUP_SYSTEM) {
-		ctl->max_stripe_size = SZ_32M;
-		ctl->max_chunk_size = 2 * ctl->max_stripe_size;
-		ctl->devs_max = min_t(int, ctl->devs_max,
-				      BTRFS_MAX_DEVS_SYS_CHUNK);
-	} else {
-		BUG();
-	}
+	space_info = btrfs_find_space_info(fs_devices->fs_info, ctl->type);
+	ASSERT(space_info);
+
+	ctl->max_stripe_size = space_info->max_stripe_size;
+	ctl->max_chunk_size = space_info->max_chunk_size;
+
+	if (ctl->type & BTRFS_BLOCK_GROUP_SYSTEM)
+		ctl->devs_max = min_t(int, ctl->devs_max, BTRFS_MAX_DEVS_SYS_CHUNK);
 
 	/* We don't want a chunk larger than 10% of writable space */
 	ctl->max_chunk_size = min(div_factor(fs_devices->total_rw_bytes, 1),
-- 
2.30.2