Re: [PATCH] btrfs: optimize free space tree bitmap conversion

[Howard McLauchlan <hmclauchlan@fb.com>]

On 04/18/2018 08:50 AM, David Sterba wrote:
> On Tue, Apr 17, 2018 at 04:19:04PM -0700, Howard McLauchlan wrote:
>> Presently, convert_free_space_to_extents() does a linear scan of the
>> bitmap. We can speed this up with find_next_{bit,zero_bit}_le().
>>
>> This patch replaces the linear scan with find_next_{bit,zero_bit}_le().
>> Testing shows a 20-33% decrease in execution time for
>> convert_free_space_to_extents().
> Sounds good.
>
>> Suggested-by: Omar Sandoval <osandov@osandov.com>
>> Signed-off-by: Howard McLauchlan <hmclauchlan@fb.com>
>> ---
>> Based on 4.17-rc1
>>
>>  fs/btrfs/extent_io.c       | 12 ++++-----
>>  fs/btrfs/extent_io.h       |  4 +--
>>  fs/btrfs/free-space-tree.c | 54 ++++++++++++++------------------------
>>  3 files changed, 27 insertions(+), 43 deletions(-)
>>
>> diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
>> index e99b329002cf..1c0e7ce49556 100644
>> --- a/fs/btrfs/extent_io.c
>> +++ b/fs/btrfs/extent_io.c
>> @@ -5620,12 +5620,12 @@ void copy_extent_buffer(struct extent_buffer *dst, struct extent_buffer *src,
>>  	}
>>  }
>>  
>> -void le_bitmap_set(u8 *map, unsigned int start, int len)
>> +void le_bitmap_set(unsigned long *map, unsigned int start, int len)
>>  {
>> -	u8 *p = map + BIT_BYTE(start);
>> +	char *p = ((char *)map) + BIT_BYTE(start);
>>  	const unsigned int size = start + len;
>>  	int bits_to_set = BITS_PER_BYTE - (start % BITS_PER_BYTE);
>> -	u8 mask_to_set = BITMAP_FIRST_BYTE_MASK(start);
>> +	char mask_to_set = BITMAP_FIRST_BYTE_MASK(start);
> Why do you switch to char? As there are bit operations done below (that
> you don't change), the unsigned type seems correct.
>
>>  
>>  	while (len - bits_to_set >= 0) {
>>  		*p |= mask_to_set;
>> @@ -5640,12 +5640,12 @@ void le_bitmap_set(u8 *map, unsigned int start, int len)
>>  	}
>>  }
>>  
>> -void le_bitmap_clear(u8 *map, unsigned int start, int len)
>> +void le_bitmap_clear(unsigned long *map, unsigned int start, int len)
>>  {
>> -	u8 *p = map + BIT_BYTE(start);
>> +	char *p = ((char *)map) + BIT_BYTE(start);
>>  	const unsigned int size = start + len;
>>  	int bits_to_clear = BITS_PER_BYTE - (start % BITS_PER_BYTE);
>> -	u8 mask_to_clear = BITMAP_FIRST_BYTE_MASK(start);
>> +	char mask_to_clear = BITMAP_FIRST_BYTE_MASK(start);
> Same here and in below. Otherwise it looks ok.
>
>>  
>>  	while (len - bits_to_clear >= 0) {
>>  		*p &= ~mask_to_clear;
>> diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h
>> index a53009694b16..a6db233f4a40 100644
>> --- a/fs/btrfs/extent_io.h
>> +++ b/fs/btrfs/extent_io.h
>> @@ -84,8 +84,8 @@ static inline int le_test_bit(int nr, const u8 *addr)
>>  	return 1U & (addr[BIT_BYTE(nr)] >> (nr & (BITS_PER_BYTE-1)));
>>  }
>>  
>> -void le_bitmap_set(u8 *map, unsigned int start, int len);
>> -void le_bitmap_clear(u8 *map, unsigned int start, int len);
>> +void le_bitmap_set(unsigned long *map, unsigned int start, int len);
>> +void le_bitmap_clear(unsigned long *map, unsigned int start, int len);
>>  
>>  struct extent_state;
>>  struct btrfs_root;
>> diff --git a/fs/btrfs/free-space-tree.c b/fs/btrfs/free-space-tree.c
>> index 32a0f6cb5594..0ddf96b01a3a 100644
>> --- a/fs/btrfs/free-space-tree.c
>> +++ b/fs/btrfs/free-space-tree.c
>> @@ -138,9 +138,9 @@ static inline u32 free_space_bitmap_size(u64 size, u32 sectorsize)
>>  	return DIV_ROUND_UP((u32)div_u64(size, sectorsize), BITS_PER_BYTE);
>>  }
>>  
>> -static u8 *alloc_bitmap(u32 bitmap_size)
>> +static unsigned long *alloc_bitmap(u32 bitmap_size)
>>  {
>> -	u8 *ret;
>> +	unsigned long *ret;
>>  	unsigned int nofs_flag;
>>  
>>  	/*
>> @@ -166,7 +166,8 @@ int convert_free_space_to_bitmaps(struct btrfs_trans_handle *trans,
>>  	struct btrfs_free_space_info *info;
>>  	struct btrfs_key key, found_key;
>>  	struct extent_buffer *leaf;
>> -	u8 *bitmap, *bitmap_cursor;
>> +	unsigned long *bitmap;
>> +	char *bitmap_cursor;
>>  	u64 start, end;
>>  	u64 bitmap_range, i;
>>  	u32 bitmap_size, flags, expected_extent_count;
>> @@ -255,7 +256,7 @@ int convert_free_space_to_bitmaps(struct btrfs_trans_handle *trans,
>>  		goto out;
>>  	}
>>  
>> -	bitmap_cursor = bitmap;
>> +	bitmap_cursor = (char *)bitmap;
>>  	bitmap_range = fs_info->sectorsize * BTRFS_FREE_SPACE_BITMAP_BITS;
>>  	i = start;
>>  	while (i < end) {
>> @@ -304,13 +305,10 @@ int convert_free_space_to_extents(struct btrfs_trans_handle *trans,
>>  	struct btrfs_free_space_info *info;
>>  	struct btrfs_key key, found_key;
>>  	struct extent_buffer *leaf;
>> -	u8 *bitmap;
>> +	unsigned long *bitmap;
>>  	u64 start, end;
>> -	/* Initialize to silence GCC. */
>> -	u64 extent_start = 0;
>> -	u64 offset;
>>  	u32 bitmap_size, flags, expected_extent_count;
>> -	int prev_bit = 0, bit, bitnr;
>> +	unsigned long nrbits, start_bit, end_bit;
>>  	u32 extent_count = 0;
>>  	int done = 0, nr;
>>  	int ret;
>> @@ -348,7 +346,7 @@ int convert_free_space_to_extents(struct btrfs_trans_handle *trans,
>>  				break;
>>  			} else if (found_key.type == BTRFS_FREE_SPACE_BITMAP_KEY) {
>>  				unsigned long ptr;
>> -				u8 *bitmap_cursor;
>> +				char *bitmap_cursor;
>>  				u32 bitmap_pos, data_size;
>>  
>>  				ASSERT(found_key.objectid >= start);
>> @@ -358,7 +356,7 @@ int convert_free_space_to_extents(struct btrfs_trans_handle *trans,
>>  				bitmap_pos = div_u64(found_key.objectid - start,
>>  						     fs_info->sectorsize *
>>  						     BITS_PER_BYTE);
>> -				bitmap_cursor = bitmap + bitmap_pos;
>> +				bitmap_cursor = ((char *)bitmap) + bitmap_pos;
>>  				data_size = free_space_bitmap_size(found_key.offset,
>>  								   fs_info->sectorsize);
>>  
>> @@ -392,32 +390,16 @@ int convert_free_space_to_extents(struct btrfs_trans_handle *trans,
>>  	btrfs_mark_buffer_dirty(leaf);
>>  	btrfs_release_path(path);
>>  
>> -	offset = start;
>> -	bitnr = 0;
>> -	while (offset < end) {
>> -		bit = !!le_test_bit(bitnr, bitmap);
>> -		if (prev_bit == 0 && bit == 1) {
>> -			extent_start = offset;
>> -		} else if (prev_bit == 1 && bit == 0) {
>> -			key.objectid = extent_start;
>> -			key.type = BTRFS_FREE_SPACE_EXTENT_KEY;
>> -			key.offset = offset - extent_start;
>> -
>> -			ret = btrfs_insert_empty_item(trans, root, path, &key, 0);
>> -			if (ret)
>> -				goto out;
>> -			btrfs_release_path(path);
>> +	nrbits = div_u64(block_group->key.offset, block_group->fs_info->sectorsize);
>> +	start_bit = find_next_bit_le(bitmap, nrbits, 0);
>>  
>> -			extent_count++;
>> -		}
>> -		prev_bit = bit;
>> -		offset += fs_info->sectorsize;
>> -		bitnr++;
>> -	}
>> -	if (prev_bit == 1) {
>> -		key.objectid = extent_start;
>> +	while (start_bit < nrbits) {
>> +		end_bit = find_next_zero_bit_le(bitmap, nrbits, start_bit);
>> +		ASSERT(start_bit < end_bit);
>> +
>> +		key.objectid = start + start_bit * block_group->fs_info->sectorsize;
>>  		key.type = BTRFS_FREE_SPACE_EXTENT_KEY;
>> -		key.offset = end - extent_start;
>> +		key.offset = (end_bit - start_bit) * block_group->fs_info->sectorsize;
>>  
>>  		ret = btrfs_insert_empty_item(trans, root, path, &key, 0);
>>  		if (ret)
>> @@ -425,6 +407,8 @@ int convert_free_space_to_extents(struct btrfs_trans_handle *trans,
>>  		btrfs_release_path(path);
>>  
>>  		extent_count++;
>> +
>> +		start_bit = find_next_bit_le(bitmap, nrbits, end_bit);
>>  	}
>>  
>>  	if (extent_count != expected_extent_count) {
>> -- 
>> 2.17.0
>>
>> --
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ah, I'll fix and send a V2. Also just realized le_bitmap_clear() isn't used, will remove.

Howard