Re: [PATCH v2 1/8] staging: erofs: add compacted ondisk compression indexes

[Gao Xiang]

Hi Chao,

On 2019/6/21 15:46, Chao Yu wrote:
> On 2019/6/21 0:07, Gao Xiang wrote:
>> This patch introduces new compacted compression indexes.
>>
>> In contract to legacy compression indexes that
>>    each 4k logical cluster has an 8-byte index,
>> compacted ondisk compression indexes will have
>>    amortized 2 bytes for each 4k logical cluster (compacted 2B)
>>    amortized 4 bytes for each 4k logical cluster (compacted 4B)
>>
>> In detail, several continuous clusters will be encoded in
>> a compacted pack with cluster types, offsets, and one blkaddr
>> at the end of the pack to leave 4-byte margin for better
>> decoding performance, as illustrated below:
>>    _____________________________________________
>>   |___@_____ encoded bits __________|_ blkaddr _|
>>   0       .                                     amortized * vcnt
>>   .          .
>>   .             .                   amortized * vcnt - 4
>>   .                .
>>   .___________________.
>>   |_type_|_clusterofs_|
>>
>> Note that compacted 2 / 4B should be aligned with 32 / 8 bytes
>> in order to avoid each pack crossing page boundary.
>>
>> Signed-off-by: Gao Xiang <gaoxiang25@xxxxxxxxxx>
>> ---
>>  drivers/staging/erofs/data.c      |  4 +--
>>  drivers/staging/erofs/erofs_fs.h  | 57 +++++++++++++++++++++++++------
>>  drivers/staging/erofs/inode.c     |  5 +--
>>  drivers/staging/erofs/internal.h  | 11 ++----
>>  drivers/staging/erofs/unzip_vle.c |  8 ++---
>>  5 files changed, 56 insertions(+), 29 deletions(-)
>>
>> diff --git a/drivers/staging/erofs/data.c b/drivers/staging/erofs/data.c
>> index 746685f90564..cc31c3e5984c 100644
>> --- a/drivers/staging/erofs/data.c
>> +++ b/drivers/staging/erofs/data.c
>> @@ -124,7 +124,7 @@ static int erofs_map_blocks_flatmode(struct inode *inode,
>>  	trace_erofs_map_blocks_flatmode_enter(inode, map, flags);
>>  
>>  	nblocks = DIV_ROUND_UP(inode->i_size, PAGE_SIZE);
>> -	lastblk = nblocks - is_inode_layout_inline(inode);
>> +	lastblk = nblocks - is_inode_flat_inline(inode);
>>  
>>  	if (unlikely(offset >= inode->i_size)) {
>>  		/* leave out-of-bound access unmapped */
>> @@ -139,7 +139,7 @@ static int erofs_map_blocks_flatmode(struct inode *inode,
>>  	if (offset < blknr_to_addr(lastblk)) {
>>  		map->m_pa = blknr_to_addr(vi->raw_blkaddr) + map->m_la;
>>  		map->m_plen = blknr_to_addr(lastblk) - offset;
>> -	} else if (is_inode_layout_inline(inode)) {
>> +	} else if (is_inode_flat_inline(inode)) {
>>  		/* 2 - inode inline B: inode, [xattrs], inline last blk... */
>>  		struct erofs_sb_info *sbi = EROFS_SB(inode->i_sb);
>>  
>> diff --git a/drivers/staging/erofs/erofs_fs.h b/drivers/staging/erofs/erofs_fs.h
>> index 8ddb2b3e7d39..a05139f1df60 100644
>> --- a/drivers/staging/erofs/erofs_fs.h
>> +++ b/drivers/staging/erofs/erofs_fs.h
>> @@ -49,19 +49,29 @@ struct erofs_super_block {
>>   * erofs inode data mapping:
>>   * 0 - inode plain without inline data A:
>>   * inode, [xattrs], ... | ... | no-holed data
>> - * 1 - inode VLE compression B:
>> + * 1 - inode VLE compression B (legacy):
>>   * inode, [xattrs], extents ... | ...
>>   * 2 - inode plain with inline data C:
>>   * inode, [xattrs], last_inline_data, ... | ... | no-holed data
>> - * 3~7 - reserved
>> + * 3 - inode compression D:
>> + * inode, [xattrs], map_header, extents ... | ...
>> + * 4~7 - reserved
>>   */
>>  enum {
>> -	EROFS_INODE_LAYOUT_PLAIN,
>> -	EROFS_INODE_LAYOUT_COMPRESSION,
>> -	EROFS_INODE_LAYOUT_INLINE,
>> +	EROFS_INODE_FLAT_PLAIN,
>> +	EROFS_INODE_FLAT_COMPRESSION_LEGACY,
>> +	EROFS_INODE_FLAT_INLINE,
>> +	EROFS_INODE_FLAT_COMPRESSION,
>>  	EROFS_INODE_LAYOUT_MAX
>>  };
>>  
>> +static bool erofs_inode_is_data_compressed(unsigned int datamode)
>> +{
>> +	if (datamode == EROFS_INODE_FLAT_COMPRESSION)
>> +		return true;
>> +	return datamode == EROFS_INODE_FLAT_COMPRESSION_LEGACY;
>> +}
>> +
>>  /* bit definitions of inode i_advise */
>>  #define EROFS_I_VERSION_BITS            1
>>  #define EROFS_I_DATA_MAPPING_BITS       3
>> @@ -176,11 +186,37 @@ struct erofs_xattr_entry {
>>  	sizeof(struct erofs_xattr_entry) + \
>>  	(entry)->e_name_len + le16_to_cpu((entry)->e_value_size))
>>  
>> -/* have to be aligned with 8 bytes on disk */
>> -struct erofs_extent_header {
>> -	__le32 eh_checksum;
>> -	__le32 eh_reserved[3];
>> -} __packed;
>> +/* available compression algorithm types */
>> +enum {
>> +	Z_EROFS_COMPRESSION_LZ4,
>> +	Z_EROFS_COMPRESSION_MAX
>> +};
>> +
>> +/*
>> + * bit 0 : COMPACTED_2B indexes (0 - off; 1 - on)
>> + *  e.g. for 4k logical cluster size,      4B        if compacted 2B is off;
>> + *                                  (4B) + 2B + (4B) if compacted 2B is on.
>> + */
>> +#define Z_EROFS_ADVISE_COMPACTED_2B_BIT         0
>> +
>> +#define Z_EROFS_ADVISE_COMPACTED_2B     (1 << Z_EROFS_ADVISE_COMPACTED_2B_BIT)
>> +
>> +struct z_erofs_map_header {
>> +	__le32	h_reserved1;
>> +	__le16	h_advise;
>> +	/*
>> +	 * bit 0-3 : algorithm type of head 1 (logical cluster type 01);
>> +	 * bit 4-7 : algorithm type of head 2 (logical cluster type 11).
>> +	 */
>> +	__u8	h_algorithmtype;
>> +	/*
>> +	 * bit 0-2 : logical cluster bits - 12, e.g. 0 for 4096;
>> +	 * bit 3-4 : (physical - logical) cluster bits of head 1:
>> +	 *       For example, if logical clustersize = 4096, 1 for 8192.
>> +	 * bit 5-7 : (physical - logical) cluster bits of head 2.
>> +	 */
>> +	__u8	h_clusterbits;
>> +};
>>  
>>  /*
>>   * Z_EROFS Variable-sized Logical Extent cluster type:
>> @@ -270,7 +306,6 @@ static inline void erofs_check_ondisk_layout_definitions(void)
>>  	BUILD_BUG_ON(sizeof(struct erofs_inode_v2) != 64);
>>  	BUILD_BUG_ON(sizeof(struct erofs_xattr_ibody_header) != 12);
>>  	BUILD_BUG_ON(sizeof(struct erofs_xattr_entry) != 4);
>> -	BUILD_BUG_ON(sizeof(struct erofs_extent_header) != 16);
>>  	BUILD_BUG_ON(sizeof(struct z_erofs_vle_decompressed_index) != 8);
>>  	BUILD_BUG_ON(sizeof(struct erofs_dirent) != 12);
>>  
>> diff --git a/drivers/staging/erofs/inode.c b/drivers/staging/erofs/inode.c
>> index e51348f7e838..3539290b8e45 100644
>> --- a/drivers/staging/erofs/inode.c
>> +++ b/drivers/staging/erofs/inode.c
>> @@ -127,12 +127,9 @@ static int fill_inline_data(struct inode *inode, void *data,
>>  {
>>  	struct erofs_vnode *vi = EROFS_V(inode);
>>  	struct erofs_sb_info *sbi = EROFS_I_SB(inode);
>> -	const int mode = vi->datamode;
>> -
>> -	DBG_BUGON(mode >= EROFS_INODE_LAYOUT_MAX);
>>  
>>  	/* should be inode inline C */
>> -	if (mode != EROFS_INODE_LAYOUT_INLINE)
>> +	if (!is_inode_flat_inline(inode))
>>  		return 0;
>>  
>>  	/* fast symlink (following ext4) */
>> diff --git a/drivers/staging/erofs/internal.h b/drivers/staging/erofs/internal.h
>> index 1666cceecb3c..c851d0be6cf6 100644
>> --- a/drivers/staging/erofs/internal.h
>> +++ b/drivers/staging/erofs/internal.h
>> @@ -382,19 +382,14 @@ static inline unsigned long inode_datablocks(struct inode *inode)
>>  	return DIV_ROUND_UP(inode->i_size, EROFS_BLKSIZ);
>>  }
>>  
>> -static inline bool is_inode_layout_plain(struct inode *inode)
>> -{
>> -	return EROFS_V(inode)->datamode == EROFS_INODE_LAYOUT_PLAIN;
>> -}
>> -
>>  static inline bool is_inode_layout_compression(struct inode *inode)
>>  {
>> -	return EROFS_V(inode)->datamode == EROFS_INODE_LAYOUT_COMPRESSION;
>> +	return erofs_inode_is_data_compressed(EROFS_V(inode)->datamode);
>>  }
>>  
>> -static inline bool is_inode_layout_inline(struct inode *inode)
>> +static inline bool is_inode_flat_inline(struct inode *inode)
>>  {
>> -	return EROFS_V(inode)->datamode == EROFS_INODE_LAYOUT_INLINE;
>> +	return EROFS_V(inode)->datamode == EROFS_INODE_FLAT_INLINE;
>>  }
>>  
>>  extern const struct super_operations erofs_sops;
>> diff --git a/drivers/staging/erofs/unzip_vle.c b/drivers/staging/erofs/unzip_vle.c
>> index f3d0d2c03939..0db9bc50f67c 100644
>> --- a/drivers/staging/erofs/unzip_vle.c
>> +++ b/drivers/staging/erofs/unzip_vle.c
>> @@ -1643,8 +1643,8 @@ vle_extent_blkaddr(struct inode *inode, pgoff_t index)
>>  	struct erofs_vnode *vi = EROFS_V(inode);
>>  
>>  	unsigned int ofs = Z_EROFS_VLE_EXTENT_ALIGN(vi->inode_isize +
>> -		vi->xattr_isize) + sizeof(struct erofs_extent_header) +
>> -		index * sizeof(struct z_erofs_vle_decompressed_index);
>> +						    vi->xattr_isize) +
>> +		16 + index * sizeof(struct z_erofs_vle_decompressed_index);
>>  
>>  	return erofs_blknr(iloc(sbi, vi->nid) + ofs);
>>  }
>> @@ -1656,8 +1656,8 @@ vle_extent_blkoff(struct inode *inode, pgoff_t index)
>>  	struct erofs_vnode *vi = EROFS_V(inode);
>>  
>>  	unsigned int ofs = Z_EROFS_VLE_EXTENT_ALIGN(vi->inode_isize +
>> -		vi->xattr_isize) + sizeof(struct erofs_extent_header) +
>> -		index * sizeof(struct z_erofs_vle_decompressed_index);
>> +						    vi->xattr_isize) +
>> +		16 + index * sizeof(struct z_erofs_vle_decompressed_index);
> 
> We can add one macro to wrap above offset (16) for better readability, anyway,
> this patch looks good to me. :)

OK, that is fine. I will add a marco to wrap up this number.
Since currently we don't read or use the legacy extent header at all, I will
make it obsoleted and remove the 16-byte legacy extent header directly.

However, in the future, I tend to add z_erofs_map_header support for the
legacy index format as well in order to support large cluster size and
more compression format, therefore it could be 8-byte z_erofs_map_header +
8-byte Z_EROFS_VLE_EXTENT_HEADER_PADDING and we need to add a requirement
field for this expension. :)

Thanks,
Gao Xiang

> 
> Reviewed-by: Chao Yu <yuchao0@xxxxxxxxxx>
> 
> Thanks,
> 
>>  
>>  	return erofs_blkoff(iloc(sbi, vi->nid) + ofs);
>>  }
>>