Re: [RFC PATCH v4 1/2] erofs: support interlaced uncompressed data for compressed files

[Gao Xiang <hsiangkao@linux.alibaba.com>]

On Tue, Sep 13, 2022 at 07:05:51PM +0800, Yue Hu wrote:
> From: Yue Hu <huyue2@coolpad.com>
> 
> Currently, uncompressed data is all handled in the shifted way, which
> means we have to shift the whole on-disk plain pcluster to get the
> logical data.   However, since we are also using in-place I/O for
> uncompressed data, data copy will be reduced a lot if pcluster is
> recorded in the interlaced way as illustrated below:
>  _______________________________________________________________
> |               |    |               |_ tail part |_ head part _|
> |<-   blk0    ->| .. |<-   blkn-2  ->|<-         blkn-1       ->|
> 
> The logical data then becomes:
>  ________________________________________________________
> |_ head part _|_  blk0  _| .. |_  blkn-2  _|_ tail part _|
> 
> In addition, non-4k plain pclusters are also survived by the
> interlaced way, which can be used for non-4k lclusters as well.
> 
> However, it's almost impossible to de-duplicate uncompressed data
> in the interlaced way, therefore shifted uncompressed data is still
> useful.
> 
> Signed-off-by: Yue Hu <huyue2@coolpad.com>

This version looks good to me,
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>

Thanks,
Gao Xiang


>  fs/erofs/decompressor.c | 47 ++++++++++++++++++++++++-----------------
>  fs/erofs/erofs_fs.h     |  2 ++
>  fs/erofs/internal.h     |  1 +
>  fs/erofs/zmap.c         | 14 ++++++++----
>  4 files changed, 41 insertions(+), 23 deletions(-)
> 
> diff --git a/fs/erofs/decompressor.c b/fs/erofs/decompressor.c
> index 2d55569f96ac..51b7ac7166d9 100644
> --- a/fs/erofs/decompressor.c
> +++ b/fs/erofs/decompressor.c
> @@ -317,52 +317,61 @@ static int z_erofs_lz4_decompress(struct z_erofs_decompress_req *rq,
>  	return ret;
>  }
>  
> -static int z_erofs_shifted_transform(struct z_erofs_decompress_req *rq,
> -				     struct page **pagepool)
> +static int z_erofs_transform_plain(struct z_erofs_decompress_req *rq,
> +				   struct page **pagepool)
>  {
> -	const unsigned int nrpages_out =
> +	const unsigned int inpages = PAGE_ALIGN(rq->inputsize) >> PAGE_SHIFT;
> +	const unsigned int outpages =
>  		PAGE_ALIGN(rq->pageofs_out + rq->outputsize) >> PAGE_SHIFT;
>  	const unsigned int righthalf = min_t(unsigned int, rq->outputsize,
>  					     PAGE_SIZE - rq->pageofs_out);
>  	const unsigned int lefthalf = rq->outputsize - righthalf;
> +	const unsigned int interlaced_offset =
> +		rq->alg == Z_EROFS_COMPRESSION_SHIFTED ? 0 : rq->pageofs_out;
>  	unsigned char *src, *dst;
>  
> -	if (nrpages_out > 2) {
> +	if (outpages > 2 && rq->alg == Z_EROFS_COMPRESSION_SHIFTED) {
>  		DBG_BUGON(1);
> -		return -EIO;
> +		return -EFSCORRUPTED;
>  	}
>  
>  	if (rq->out[0] == *rq->in) {
> -		DBG_BUGON(nrpages_out != 1);
> +		DBG_BUGON(rq->pageofs_out);
>  		return 0;
>  	}
>  
> -	src = kmap_atomic(*rq->in) + rq->pageofs_in;
> +	src = kmap_local_page(rq->in[inpages - 1]) + rq->pageofs_in;
>  	if (rq->out[0]) {
> -		dst = kmap_atomic(rq->out[0]);
> -		memcpy(dst + rq->pageofs_out, src, righthalf);
> -		kunmap_atomic(dst);
> +		dst = kmap_local_page(rq->out[0]);
> +		memcpy(dst + rq->pageofs_out, src + interlaced_offset,
> +		       righthalf);
> +		kunmap_local(dst);
>  	}
>  
> -	if (nrpages_out == 2) {
> -		DBG_BUGON(!rq->out[1]);
> -		if (rq->out[1] == *rq->in) {
> +	if (outpages > inpages) {
> +		DBG_BUGON(!rq->out[outpages - 1]);
> +		if (rq->out[outpages - 1] != rq->in[inpages - 1]) {
> +			dst = kmap_local_page(rq->out[outpages - 1]);
> +			memcpy(dst, interlaced_offset ? src :
> +					(src + righthalf), lefthalf);
> +			kunmap_local(dst);
> +		} else if (!interlaced_offset) {
>  			memmove(src, src + righthalf, lefthalf);
> -		} else {
> -			dst = kmap_atomic(rq->out[1]);
> -			memcpy(dst, src + righthalf, lefthalf);
> -			kunmap_atomic(dst);
>  		}
>  	}
> -	kunmap_atomic(src);
> +	kunmap_local(src);
>  	return 0;
>  }
>  
>  static struct z_erofs_decompressor decompressors[] = {
>  	[Z_EROFS_COMPRESSION_SHIFTED] = {
> -		.decompress = z_erofs_shifted_transform,
> +		.decompress = z_erofs_transform_plain,
>  		.name = "shifted"
>  	},
> +	[Z_EROFS_COMPRESSION_INTERLACED] = {
> +		.decompress = z_erofs_transform_plain,
> +		.name = "interlaced"
> +	},
>  	[Z_EROFS_COMPRESSION_LZ4] = {
>  		.decompress = z_erofs_lz4_decompress,
>  		.name = "lz4"
> diff --git a/fs/erofs/erofs_fs.h b/fs/erofs/erofs_fs.h
> index 2b48373f690b..5c1de6d7ad71 100644
> --- a/fs/erofs/erofs_fs.h
> +++ b/fs/erofs/erofs_fs.h
> @@ -295,11 +295,13 @@ struct z_erofs_lzma_cfgs {
>   * bit 1 : HEAD1 big pcluster (0 - off; 1 - on)
>   * bit 2 : HEAD2 big pcluster (0 - off; 1 - on)
>   * bit 3 : tailpacking inline pcluster (0 - off; 1 - on)
> + * bit 4 : interlaced plain pcluster (0 - off; 1 - on)
>   */
>  #define Z_EROFS_ADVISE_COMPACTED_2B		0x0001
>  #define Z_EROFS_ADVISE_BIG_PCLUSTER_1		0x0002
>  #define Z_EROFS_ADVISE_BIG_PCLUSTER_2		0x0004
>  #define Z_EROFS_ADVISE_INLINE_PCLUSTER		0x0008
> +#define Z_EROFS_ADVISE_INTERLACED_PCLUSTER	0x0010
>  
>  struct z_erofs_map_header {
>  	__le16	h_reserved1;
> diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
> index cfee49d33b95..f3ed36445d73 100644
> --- a/fs/erofs/internal.h
> +++ b/fs/erofs/internal.h
> @@ -436,6 +436,7 @@ struct erofs_map_blocks {
>  
>  enum {
>  	Z_EROFS_COMPRESSION_SHIFTED = Z_EROFS_COMPRESSION_MAX,
> +	Z_EROFS_COMPRESSION_INTERLACED,
>  	Z_EROFS_COMPRESSION_RUNTIME_MAX
>  };
>  
> diff --git a/fs/erofs/zmap.c b/fs/erofs/zmap.c
> index d58549ca1df9..7196235a441c 100644
> --- a/fs/erofs/zmap.c
> +++ b/fs/erofs/zmap.c
> @@ -679,12 +679,18 @@ static int z_erofs_do_map_blocks(struct inode *inode,
>  			goto out;
>  	}
>  
> -	if (m.headtype == Z_EROFS_VLE_CLUSTER_TYPE_PLAIN)
> -		map->m_algorithmformat = Z_EROFS_COMPRESSION_SHIFTED;
> -	else if (m.headtype == Z_EROFS_VLE_CLUSTER_TYPE_HEAD2)
> +	if (m.headtype == Z_EROFS_VLE_CLUSTER_TYPE_PLAIN) {
> +		if (vi->z_advise & Z_EROFS_ADVISE_INTERLACED_PCLUSTER)
> +			map->m_algorithmformat =
> +				Z_EROFS_COMPRESSION_INTERLACED;
> +		else
> +			map->m_algorithmformat =
> +				Z_EROFS_COMPRESSION_SHIFTED;
> +	} else if (m.headtype == Z_EROFS_VLE_CLUSTER_TYPE_HEAD2) {
>  		map->m_algorithmformat = vi->z_algorithmtype[1];
> -	else
> +	} else {
>  		map->m_algorithmformat = vi->z_algorithmtype[0];
> +	}
>  
>  	if ((flags & EROFS_GET_BLOCKS_FIEMAP) ||
>  	    ((flags & EROFS_GET_BLOCKS_READMORE) &&
> -- 
> 2.17.1