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Date:   Thu, 25 Aug 2022 11:23:44 +0800
From:   Gao Xiang <hsiangkao@linux.alibaba.com>
To:     Yue Hu <zbestahu@gmail.com>
Cc:     xiang@kernel.org, chao@kernel.org, linux-erofs@lists.ozlabs.org,
        linux-kernel@vger.kernel.org, zhangwen@coolpad.com,
        Yue Hu <huyue2@coolpad.com>
Subject: Re: [RFC PATCH 2/2] erofs: add on-disk compressed fragments support
Message-ID: <YwbrQF315/Sh41/D@B-P7TQMD6M-0146.local>
References: <cover.1661146058.git.huyue2@coolpad.com>
 <b087322de2adfd8ce39a5d380191562b0b0e0086.1661146058.git.huyue2@coolpad.com>
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In-Reply-To: <b087322de2adfd8ce39a5d380191562b0b0e0086.1661146058.git.huyue2@coolpad.com>
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Hi Yue,

On Mon, Aug 22, 2022 at 01:53:01PM +0800, Yue Hu wrote:
> From: Yue Hu <huyue2@coolpad.com>
> 
> Introduce on-disk compressed fragments feature.
> 
> This approach adds a new field called `h_fragmentoff' in the per-file
> compression header to indicate the fragment offset of each tail pcluster
> or the whole file in the special packed inode.
> 
> Like ztailpacking, it will also find and record the 'headlcn' of the
> tail pcluster when initializing per-inode zmap for making follow-on
> requests more easy.
> 
> Moreover, enable the offset for shifted decompression since we are
> writing from 'pageofs_ofs' when compressing if this feature is used.
> 
> Signed-off-by: Yue Hu <huyue2@coolpad.com>
> ---
>  fs/erofs/decompressor.c |  4 +--
>  fs/erofs/erofs_fs.h     | 26 ++++++++++++++-----
>  fs/erofs/internal.h     | 16 +++++++++---
>  fs/erofs/super.c        |  6 +++++
>  fs/erofs/sysfs.c        |  2 ++
>  fs/erofs/zdata.c        | 55 ++++++++++++++++++++++++++++++++++++++++-
>  fs/erofs/zmap.c         | 40 +++++++++++++++++++++++++++---
>  7 files changed, 133 insertions(+), 16 deletions(-)
> 
> diff --git a/fs/erofs/decompressor.c b/fs/erofs/decompressor.c
> index dc02d95b52d7..fe4a34ac2de7 100644
> --- a/fs/erofs/decompressor.c
> +++ b/fs/erofs/decompressor.c
> @@ -338,8 +338,8 @@ static int z_erofs_shifted_transform(struct z_erofs_decompress_req *rq,
>  		return 0;
>  	}
>  
> -	/* set it to pageofs_out if fragments feature is used */
> -	headofs_in = 0;
> +	headofs_in = !erofs_sb_has_fragments(EROFS_SB(rq->sb)) ? 0 :

Same as I pointed out in the erofs-utils series.

> +		     rq->pageofs_out;
>  
>  	src = kmap_atomic(*rq->in) + rq->pageofs_in;
>  	if (rq->out[0]) {
> diff --git a/fs/erofs/erofs_fs.h b/fs/erofs/erofs_fs.h
> index 2b48373f690b..3306cca5f03b 100644
> --- a/fs/erofs/erofs_fs.h
> +++ b/fs/erofs/erofs_fs.h
> @@ -25,6 +25,7 @@
>  #define EROFS_FEATURE_INCOMPAT_DEVICE_TABLE	0x00000008
>  #define EROFS_FEATURE_INCOMPAT_COMPR_HEAD2	0x00000008
>  #define EROFS_FEATURE_INCOMPAT_ZTAILPACKING	0x00000010
> +#define EROFS_FEATURE_INCOMPAT_FRAGMENTS	0x00000020
>  #define EROFS_ALL_FEATURE_INCOMPAT		\
>  	(EROFS_FEATURE_INCOMPAT_ZERO_PADDING | \
>  	 EROFS_FEATURE_INCOMPAT_COMPR_CFGS | \
> @@ -32,7 +33,8 @@
>  	 EROFS_FEATURE_INCOMPAT_CHUNKED_FILE | \
>  	 EROFS_FEATURE_INCOMPAT_DEVICE_TABLE | \
>  	 EROFS_FEATURE_INCOMPAT_COMPR_HEAD2 | \
> -	 EROFS_FEATURE_INCOMPAT_ZTAILPACKING)
> +	 EROFS_FEATURE_INCOMPAT_ZTAILPACKING | \
> +	 EROFS_FEATURE_INCOMPAT_FRAGMENTS)
>  
>  #define EROFS_SB_EXTSLOT_SIZE	16
>  
> @@ -71,7 +73,9 @@ struct erofs_super_block {
>  	} __packed u1;
>  	__le16 extra_devices;	/* # of devices besides the primary device */
>  	__le16 devt_slotoff;	/* startoff = devt_slotoff * devt_slotsize */
> -	__u8 reserved2[38];
> +	__u8 reserved[6];
> +	__le64 packed_nid;	/* nid of the special packed inode */
> +	__u8 reserved2[24];
>  };
>  
>  /*
> @@ -295,16 +299,25 @@ 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 : fragment 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_FRAGMENT_PCLUSTER	0x0010
>  
> +#define Z_EROFS_FRAGMENT_INODE_BIT              7
>  struct z_erofs_map_header {
> -	__le16	h_reserved1;
> -	/* indicates the encoded size of tailpacking data */
> -	__le16  h_idata_size;
> +	union {
> +		/* direct addressing for fragment offset */
> +		__le32  h_fragmentoff;
> +		struct {
> +			__le16  h_reserved1;
> +			/* indicates the encoded size of tailpacking data */
> +			__le16  h_idata_size;
> +		};
> +	};
>  	__le16	h_advise;
>  	/*
>  	 * bit 0-3 : algorithm type of head 1 (logical cluster type 01);
> @@ -313,7 +326,8 @@ struct z_erofs_map_header {
>  	__u8	h_algorithmtype;
>  	/*
>  	 * bit 0-2 : logical cluster bits - 12, e.g. 0 for 4096;
> -	 * bit 3-7 : reserved.
> +	 * bit 3-6 : reserved;
> +	 * bit 7   : move the whole file into packed inode or not.
>  	 */
>  	__u8	h_clusterbits;
>  };
> diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
> index cfee49d33b95..7b9d31bab928 100644
> --- a/fs/erofs/internal.h
> +++ b/fs/erofs/internal.h
> @@ -120,6 +120,7 @@ struct erofs_sb_info {
>  	struct inode *managed_cache;
>  
>  	struct erofs_sb_lz4_info lz4;
> +	struct inode *packed_inode;
>  #endif	/* CONFIG_EROFS_FS_ZIP */
>  	struct erofs_dev_context *devs;
>  	struct dax_device *dax_dev;
> @@ -306,6 +307,7 @@ EROFS_FEATURE_FUNCS(chunked_file, incompat, INCOMPAT_CHUNKED_FILE)
>  EROFS_FEATURE_FUNCS(device_table, incompat, INCOMPAT_DEVICE_TABLE)
>  EROFS_FEATURE_FUNCS(compr_head2, incompat, INCOMPAT_COMPR_HEAD2)
>  EROFS_FEATURE_FUNCS(ztailpacking, incompat, INCOMPAT_ZTAILPACKING)
> +EROFS_FEATURE_FUNCS(fragments, incompat, INCOMPAT_FRAGMENTS)
>  EROFS_FEATURE_FUNCS(sb_chksum, compat, COMPAT_SB_CHKSUM)
>  
>  /* atomic flag definitions */
> @@ -341,8 +343,13 @@ struct erofs_inode {
>  			unsigned char  z_algorithmtype[2];
>  			unsigned char  z_logical_clusterbits;
>  			unsigned long  z_tailextent_headlcn;
> -			erofs_off_t    z_idataoff;
> -			unsigned short z_idata_size;
> +			union {
> +				struct {
> +					erofs_off_t    z_idataoff;
> +					unsigned short z_idata_size;
> +				};
> +				erofs_off_t z_fragmentoff;
> +			};
>  		};
>  #endif	/* CONFIG_EROFS_FS_ZIP */
>  	};
> @@ -400,6 +407,7 @@ extern const struct address_space_operations z_erofs_aops;
>  enum {
>  	BH_Encoded = BH_PrivateStart,
>  	BH_FullMapped,
> +	BH_Fragment,
>  };
>  
>  /* Has a disk mapping */
> @@ -410,6 +418,8 @@ enum {
>  #define EROFS_MAP_ENCODED	(1 << BH_Encoded)
>  /* The length of extent is full */
>  #define EROFS_MAP_FULL_MAPPED	(1 << BH_FullMapped)
> +/* Located in the special packed inode */
> +#define EROFS_MAP_FRAGMENT	(1 << BH_Fragment)
>  
>  struct erofs_map_blocks {
>  	struct erofs_buf buf;
> @@ -431,7 +441,7 @@ struct erofs_map_blocks {
>  #define EROFS_GET_BLOCKS_FIEMAP	0x0002
>  /* Used to map the whole extent if non-negligible data is requested for LZMA */
>  #define EROFS_GET_BLOCKS_READMORE	0x0004
> -/* Used to map tail extent for tailpacking inline pcluster */
> +/* Used to map tail extent for tailpacking inline or fragment pcluster */
>  #define EROFS_GET_BLOCKS_FINDTAIL	0x0008
>  
>  enum {
> diff --git a/fs/erofs/super.c b/fs/erofs/super.c
> index 3173debeaa5a..fde5ece36b2c 100644
> --- a/fs/erofs/super.c
> +++ b/fs/erofs/super.c
> @@ -381,6 +381,8 @@ static int erofs_read_superblock(struct super_block *sb)
>  #endif
>  	sbi->islotbits = ilog2(sizeof(struct erofs_inode_compact));
>  	sbi->root_nid = le16_to_cpu(dsb->root_nid);
> +	sbi->packed_inode = erofs_sb_has_fragments(sbi) ?
> +		erofs_iget(sb, le64_to_cpu(dsb->packed_nid), false) : NULL;

iget could fail, what will we do next in such case?

>  	sbi->inos = le64_to_cpu(dsb->inos);
>  
>  	sbi->build_time = le64_to_cpu(dsb->build_time);
> @@ -411,6 +413,8 @@ static int erofs_read_superblock(struct super_block *sb)
>  		erofs_info(sb, "EXPERIMENTAL compressed inline data feature in use. Use at your own risk!");
>  	if (erofs_is_fscache_mode(sb))
>  		erofs_info(sb, "EXPERIMENTAL fscache-based on-demand read feature in use. Use at your own risk!");
> +	if (erofs_sb_has_fragments(sbi))
> +		erofs_info(sb, "EXPERIMENTAL compressed fragments feature in use. Use at your own risk!");
>  out:
>  	erofs_put_metabuf(&buf);
>  	return ret;
> @@ -908,6 +912,8 @@ static void erofs_put_super(struct super_block *sb)
>  #ifdef CONFIG_EROFS_FS_ZIP
>  	iput(sbi->managed_cache);
>  	sbi->managed_cache = NULL;
> +	iput(sbi->packed_inode);
> +	sbi->packed_inode = NULL;
>  #endif
>  	erofs_fscache_unregister_cookie(&sbi->s_fscache);
>  }
> diff --git a/fs/erofs/sysfs.c b/fs/erofs/sysfs.c
> index c1383e508bbe..1b52395be82a 100644
> --- a/fs/erofs/sysfs.c
> +++ b/fs/erofs/sysfs.c
> @@ -76,6 +76,7 @@ EROFS_ATTR_FEATURE(device_table);
>  EROFS_ATTR_FEATURE(compr_head2);
>  EROFS_ATTR_FEATURE(sb_chksum);
>  EROFS_ATTR_FEATURE(ztailpacking);
> +EROFS_ATTR_FEATURE(fragments);
>  
>  static struct attribute *erofs_feat_attrs[] = {
>  	ATTR_LIST(zero_padding),
> @@ -86,6 +87,7 @@ static struct attribute *erofs_feat_attrs[] = {
>  	ATTR_LIST(compr_head2),
>  	ATTR_LIST(sb_chksum),
>  	ATTR_LIST(ztailpacking),
> +	ATTR_LIST(fragments),
>  	NULL,
>  };
>  ATTRIBUTE_GROUPS(erofs_feat);
> diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
> index 5792ca9e0d5e..3dd3b829766f 100644
> --- a/fs/erofs/zdata.c
> +++ b/fs/erofs/zdata.c
> @@ -650,6 +650,33 @@ static bool should_alloc_managed_pages(struct z_erofs_decompress_frontend *fe,
>  		la < fe->headoffset;
>  }
>  
> +static int z_erofs_read_fragment_data(struct page *page, unsigned int pageofs,
> +				      loff_t start, unsigned int len)
> +{
> +	struct inode *const inode = page->mapping->host;
> +	erofs_off_t offset = EROFS_I(inode)->z_fragmentoff + start;
> +	struct erofs_buf buf = __EROFS_BUF_INITIALIZER;
> +	u8 *src, *dst;
> +	unsigned int i, cnt;
> +
> +	for (i = 0; i < len; i += cnt) {
> +		cnt = min(EROFS_BLKSIZ - (unsigned int)erofs_blkoff(offset),
> +			  len - i);
> +		src = erofs_bread(&buf, EROFS_I_SB(inode)->packed_inode,
> +				  erofs_blknr(offset), EROFS_KMAP);
> +		if (IS_ERR(src))
> +			return PTR_ERR(src);
> +
> +		dst = kmap_atomic(page);
> +		memcpy(dst + pageofs + i, src + erofs_blkoff(offset), cnt);
> +		kunmap_atomic(dst);

Use kmap_local_page instead.

> +
> +		offset += cnt;
> +	}
> +	erofs_put_metabuf(&buf);
> +	return 0;
> +}
> +
>  static int z_erofs_do_read_page(struct z_erofs_decompress_frontend *fe,
>  				struct page *page, struct page **pagepool)
>  {
> @@ -688,7 +715,8 @@ static int z_erofs_do_read_page(struct z_erofs_decompress_frontend *fe,
>  		/* didn't get a valid pcluster previously (very rare) */
>  	}
>  
> -	if (!(map->m_flags & EROFS_MAP_MAPPED))
> +	if (!(map->m_flags & EROFS_MAP_MAPPED) ||
> +	    map->m_flags & EROFS_MAP_FRAGMENT)
>  		goto hitted;
>  
>  	err = z_erofs_collector_begin(fe);
> @@ -735,6 +763,31 @@ static int z_erofs_do_read_page(struct z_erofs_decompress_frontend *fe,
>  		zero_user_segment(page, cur, end);
>  		goto next_part;
>  	}
> +	if (map->m_flags & EROFS_MAP_FRAGMENT) {
> +		unsigned int pageofs, skip, len;
> +
> +		if (!map->m_la) {
> +			len = (offset + cur + 1 == inode->i_size) ? (cur + 1) :
> +			      end;
> +			err = z_erofs_read_fragment_data(page, 0, offset, len);
> +			goto out;
> +		}
> +		if (map->m_la < offset) {
> +			pageofs = 0;
> +			skip = offset - map->m_la;
> +		} else {
> +			pageofs = map->m_la & ~PAGE_MASK;
> +			skip = 0;
> +		}
> +		DBG_BUGON(map->m_llen - skip > PAGE_SIZE);

		len = min(map->m_llen - skip, end - cur)?

> +		err = z_erofs_read_fragment_data(page, pageofs, skip,
> +						 map->m_llen - skip);

						 len); ?

Thanks,
Gao Xiang