[RFC] Btrfs: Allow the compressed extent size limit to be modified v2

[Mitch Harder <mitch.harder@sabayonlinux.org>]

Provide for modification of the limit of compressed extent size
utilizing mount-time configuration settings.

The size of compressed extents was limited to 128K, which
leads to fragmentation of the extents (although the extents
themselves may still be located contiguously).  This limit is
put in place to ease the RAM required when spreading compression
across several CPUs, and to make sure the amount of IO required
to do a random read is reasonably small.

Signed-off-by: Mitch Harder <mitch.harder@sabayonlinux.org>
---
Changelog v1 -> v2:
- Use more self-documenting variable name:
  compressed_extent_size -> max_compressed_extent_kb
- Use #define BTRFS_DEFAULT_MAX_COMPR_EXTENTS instead of raw 128.
- Fix min calculation for nr_pages.
- Comment cleanup.
- Use more self-documenting mount option parameter:
  compressed_extent_size -> max_compressed_extent_kb
- Fix formatting in btrfs_show_options.
---
 fs/btrfs/ctree.h      |  6 ++++++
 fs/btrfs/disk-io.c    |  1 +
 fs/btrfs/inode.c      |  8 ++++----
 fs/btrfs/relocation.c |  7 ++++---
 fs/btrfs/super.c      | 20 +++++++++++++++++++-
 5 files changed, 34 insertions(+), 8 deletions(-)

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 547b7b0..a62f20c 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -191,6 +191,9 @@ static int btrfs_csum_sizes[] = { 4, 0 };
 /* ioprio of readahead is set to idle */
 #define BTRFS_IOPRIO_READA (IOPRIO_PRIO_VALUE(IOPRIO_CLASS_IDLE, 0))
 
+/* Default value for maximum compressed extent size (kb) */
+#define BTRFS_DEFAULT_MAX_COMPR_EXTENTS	128
+
 /*
  * The key defines the order in the tree, and so it also defines (optimal)
  * block layout.
@@ -1477,6 +1480,8 @@ struct btrfs_fs_info {
 	unsigned data_chunk_allocations;
 	unsigned metadata_ratio;
 
+	unsigned max_compressed_extent_kb;
+
 	void *bdev_holder;
 
 	/* private scrub information */
@@ -1829,6 +1834,7 @@ struct btrfs_ioctl_defrag_range_args {
 #define BTRFS_MOUNT_CHECK_INTEGRITY	(1 << 20)
 #define BTRFS_MOUNT_CHECK_INTEGRITY_INCLUDING_EXTENT_DATA (1 << 21)
 #define BTRFS_MOUNT_PANIC_ON_FATAL_ERROR	(1 << 22)
+#define BTRFS_MOUNT_COMPR_EXTENT_SIZE (1 << 23)
 
 #define btrfs_clear_opt(o, opt)		((o) &= ~BTRFS_MOUNT_##opt)
 #define btrfs_set_opt(o, opt)		((o) |= BTRFS_MOUNT_##opt)
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 830bc17..775e7ba 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -2056,6 +2056,7 @@ int open_ctree(struct super_block *sb,
 	fs_info->trans_no_join = 0;
 	fs_info->free_chunk_space = 0;
 	fs_info->tree_mod_log = RB_ROOT;
+	fs_info->max_compressed_extent_kb = BTRFS_DEFAULT_MAX_COMPR_EXTENTS;
 
 	/* readahead state */
 	INIT_RADIX_TREE(&fs_info->reada_tree, GFP_NOFS & ~__GFP_WAIT);
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 148abeb..78fc6eb 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -346,8 +346,8 @@ static noinline int compress_file_range(struct inode *inode,
 	unsigned long nr_pages_ret = 0;
 	unsigned long total_compressed = 0;
 	unsigned long total_in = 0;
-	unsigned long max_compressed = 128 * 1024;
-	unsigned long max_uncompressed = 128 * 1024;
+	unsigned long max_compressed = root->fs_info->max_compressed_extent_kb * 1024;
+	unsigned long max_uncompressed = root->fs_info->max_compressed_extent_kb * 1024;
 	int i;
 	int will_compress;
 	int compress_type = root->fs_info->compress_type;
@@ -361,7 +361,7 @@ static noinline int compress_file_range(struct inode *inode,
 again:
 	will_compress = 0;
 	nr_pages = (end >> PAGE_CACHE_SHIFT) - (start >> PAGE_CACHE_SHIFT) + 1;
-	nr_pages = min(nr_pages, (128 * 1024UL) / PAGE_CACHE_SIZE);
+	nr_pages = min(nr_pages, max_compressed / PAGE_CACHE_SIZE);
 
 	/*
 	 * we don't want to send crud past the end of i_size through
@@ -386,7 +386,7 @@ again:
 	 *
 	 * We also want to make sure the amount of IO required to do
 	 * a random read is reasonably small, so we limit the size of
-	 * a compressed extent to 128k.
+	 * a compressed extent.
 	 */
 	total_compressed = min(total_compressed, max_uncompressed);
 	num_bytes = (end - start + blocksize) & ~(blocksize - 1);
diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index 300e09a..64bbc9e 100644
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -144,7 +144,7 @@ struct tree_block {
 	unsigned int key_ready:1;
 };
 
-#define MAX_EXTENTS 128
+#define MAX_EXTENTS 512
 
 struct file_extent_cluster {
 	u64 start;
@@ -3055,6 +3055,7 @@ int relocate_data_extent(struct inode *inode, struct btrfs_key *extent_key,
 			 struct file_extent_cluster *cluster)
 {
 	int ret;
+	struct btrfs_fs_info *fs_info = BTRFS_I(inode)->root->fs_info;
 
 	if (cluster->nr > 0 && extent_key->objectid != cluster->end + 1) {
 		ret = relocate_file_extent_cluster(inode, cluster);
@@ -3066,12 +3067,12 @@ int relocate_data_extent(struct inode *inode, struct btrfs_key *extent_key,
 	if (!cluster->nr)
 		cluster->start = extent_key->objectid;
 	else
-		BUG_ON(cluster->nr >= MAX_EXTENTS);
+		BUG_ON(cluster->nr >= fs_info->max_compressed_extent_kb);
 	cluster->end = extent_key->objectid + extent_key->offset - 1;
 	cluster->boundary[cluster->nr] = extent_key->objectid;
 	cluster->nr++;
 
-	if (cluster->nr >= MAX_EXTENTS) {
+	if (cluster->nr >= fs_info->max_compressed_extent_kb) {
 		ret = relocate_file_extent_cluster(inode, cluster);
 		if (ret)
 			return ret;
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index d8982e9..25b8dc2 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -322,7 +322,7 @@ enum {
 	Opt_no_space_cache, Opt_recovery, Opt_skip_balance,
 	Opt_check_integrity, Opt_check_integrity_including_extent_data,
 	Opt_check_integrity_print_mask, Opt_fatal_errors,
-	Opt_err,
+	Opt_max_compr_extent_kb, Opt_err,
 };
 
 static match_table_t tokens = {
@@ -361,6 +361,7 @@ static match_table_t tokens = {
 	{Opt_check_integrity, "check_int"},
 	{Opt_check_integrity_including_extent_data, "check_int_data"},
 	{Opt_check_integrity_print_mask, "check_int_print_mask=%d"},
+	{Opt_max_compr_extent_kb, "max_compressed_extent_kb=%d"},
 	{Opt_fatal_errors, "fatal_errors=%s"},
 	{Opt_err, NULL},
 };
@@ -612,6 +613,20 @@ int btrfs_parse_options(struct btrfs_root *root, char *options)
 			ret = -EINVAL;
 			goto out;
 #endif
+		case Opt_max_compr_extent_kb:
+			intarg = 0;
+			match_int(&args[0], &intarg);
+			if ((intarg == 128) || (intarg == 512)) {
+				info->max_compressed_extent_kb = intarg;
+				printk(KERN_INFO "btrfs: "
+				       "max compressed extent size %d KB\n",
+				       info->max_compressed_extent_kb);
+			} else {
+				printk(KERN_INFO "btrfs: "
+				       "Invalid compressed extent size,"
+				       " using default.\n");
+			}
+			break;
 		case Opt_fatal_errors:
 			if (strcmp(args[0].from, "panic") == 0)
 				btrfs_set_opt(info->mount_opt,
@@ -951,6 +966,9 @@ static int btrfs_show_options(struct seq_file *seq, struct dentry *dentry)
 		seq_puts(seq, ",skip_balance");
 	if (btrfs_test_opt(root, PANIC_ON_FATAL_ERROR))
 		seq_puts(seq, ",fatal_errors=panic");
+	if (btrfs_test_opt(root, COMPR_EXTENT_SIZE))
+		seq_printf(seq, ",max_compressed_extent_kb=%u",
+			   info->max_compressed_extent_kb);
 	return 0;
 }
 
-- 
1.7.12.4