Btrfs devel - Feb 2013 - [RFC] Btrfs: Allow the compressed extent size limit to be modified v2

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

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On Thu, Feb 07, 2013 at 03:38:34PM -0600, Mitch Harder
wrote:
> 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.
Cool, thanks for cleaning those up.  It looks a lot better now.

- z
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On Thu, Feb 07, 2013 at 03:38:34PM -0600, Mitch Harder
wrote:
> --- 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
Is this really related to compression? IIRC I''ve seen it only in
context
of batch work in reloc, but not anywhere near compression. (I may be
wrong of course, just checking).

david
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On Thu, Feb 7, 2013 at 6:28 PM, David Sterba <dave@jikos.cz>
wrote:
> On Thu, Feb 07, 2013 at 03:38:34PM -0600, Mitch Harder wrote:
>> --- 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
>
> Is this really related to compression? IIRC I''ve seen it only in
context
> of batch work in reloc, but not anywhere near compression. (I may be
> wrong of course, just checking).
>
When you defragment compressed extents, it will run through relocation.

If autodefrag is enabled, I found most everything I touched was
running through relocation.

It has been a while since I looked at the issue, but I think balancing
your data will also run through relocation.
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On Thu, Feb 07, 2013 at 11:17:46PM -0600, Mitch Harder
wrote:
> On Thu, Feb 7, 2013 at 6:28 PM, David Sterba <dave@jikos.cz> wrote:
> > On Thu, Feb 07, 2013 at 03:38:34PM -0600, Mitch Harder wrote:
> >> --- 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
> >
> > Is this really related to compression? IIRC I''ve seen it only
in context
> > of batch work in reloc, but not anywhere near compression. (I may be
> > wrong of course, just checking).
> >
> 
> When you defragment compressed extents, it will run through relocation.
>
> If autodefrag is enabled, I found most everything I touched was
> running through relocation.
AFAIK defragmentation runs through the writeback loop, blocks are marked
dirty, delalloc tries to make them contiguous and then synced back to
disk. Autodefrag uses the same loop, just affects newly written data.
> It has been a while since I looked at the issue, but I think balancing
> your data will also run through relocation.
Balance does go through reloc for sure.

From the commit that introduces MAX_EXTENTS it''s imo quite clear that
it''s only a balance speedup:

(0257bb82d21bedff26541bcf12f1461c23f9ed61)
Btrfs: relocate file extents in clusters

The extent relocation code copy file extents one by one when
relocating data block group. This is inefficient if file
extents are small. This patch makes the relocation code copy
file extents in clusters. So we can can make better use of
read-ahead.
---

david
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On Fri, Feb 8, 2013 at 8:53 AM, David Sterba <dsterba@suse.cz>
wrote:
> On Thu, Feb 07, 2013 at 11:17:46PM -0600, Mitch Harder wrote:
>> On Thu, Feb 7, 2013 at 6:28 PM, David Sterba <dave@jikos.cz>
wrote:
>> > On Thu, Feb 07, 2013 at 03:38:34PM -0600, Mitch Harder wrote:
>> >> --- 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
>> >
>> > Is this really related to compression? IIRC I''ve seen it
only in context
>> > of batch work in reloc, but not anywhere near compression. (I may
be
>> > wrong of course, just checking).
>> >
>>
>> When you defragment compressed extents, it will run through relocation.
>>
>> If autodefrag is enabled, I found most everything I touched was
>> running through relocation.
>
> AFAIK defragmentation runs through the writeback loop, blocks are marked
> dirty, delalloc tries to make them contiguous and then synced back to
> disk. Autodefrag uses the same loop, just affects newly written data.
>
>> It has been a while since I looked at the issue, but I think balancing
>> your data will also run through relocation.
>
> Balance does go through reloc for sure.
>
> From the commit that introduces MAX_EXTENTS it''s imo quite clear
that
> it''s only a balance speedup:
>
> (0257bb82d21bedff26541bcf12f1461c23f9ed61)
> Btrfs: relocate file extents in clusters
>
> The extent relocation code copy file extents one by one when
> relocating data block group. This is inefficient if file
> extents are small. This patch makes the relocation code copy
> file extents in clusters. So we can can make better use of
> read-ahead.
In an earlier version of the patch, I had the changes to relocation.c
in a separate patch.  But, I couldn''t consistently attain the changed
maximum extent size unless I also addressed the issue with relocation.
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On Thu, Feb 07, 2013 at 03:38:34PM -0600, Mitch Harder
wrote:
> --- 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
I''m still not convinced this is needed and seeing
max_compressed_extent_kb used in the middle of relocation code makes me
wonder. There may be a bug related to the number but I have doubts that
it is related to compression.
> -		BUG_ON(cluster->nr >= MAX_EXTENTS);
> +		BUG_ON(cluster->nr >= fs_info->max_compressed_extent_kb);
...
> @@ -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);
				btrfs_set_opt(fs_info->mount_opt,
					COMPR_EXTENT_SIZE);

otherwise the value of the options is not visible in /proc/mounts
> +			} 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,
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On Thu, Feb 07, 2013 at 03:38:34PM -0600, Mitch Harder
wrote:
> 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;
MAX_EXTENTS is irrelevant to compress, it''s just for efficiency of
relocation.

thanks,
liubo

> 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
> 
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On Thu, Feb 07, 2013 at 03:38:34PM -0600, Mitch Harder
wrote:
> @@ -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"},
Can we possibly find a name that one can remember? I had to copy&paste
it each time. Let''s say something with ''compress-''
prefix, maybe
compress-extent-kb (or with underscores for "consistency").

david
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