Commit d4088803 authored by Qu Wenruo's avatar Qu Wenruo Committed by David Sterba
Browse files

btrfs: subpage: make lzo_compress_pages() compatible 



There are several problems in lzo_compress_pages() preventing it from
being subpage compatible:

- No page offset is calculated when reading from inode pages
  For subpage case, we could have @start which is not aligned to
  PAGE_SIZE.

  Thus the destination where we read data from must take offset in page
  into consideration.

- The padding for segment header is bound to PAGE_SIZE
  This means, for subpage case we can skip several corners where on x86
  machines we need to add padding zeros.

The rework will:

- Update the comment to replace "page" with "sector"

- Introduce a new helper, copy_compressed_data_to_page(), to do the copy
  So that we don't need to bother page switching for both input and
  output.

  Now in lzo_compress_pages() we only care about page switching for
  input, while in copy_compressed_data_to_page() we only care about the
  page switching for output.

- Only one main cursor
  For lzo_compress_pages() we use @cur_in as main cursor.
  It will be the file offset we are currently at.

  All other helper variables will be only declared inside the loop.

  For copy_compressed_data_to_page() it's similar, we will have
  @cur_out at the main cursor, which records how many bytes are in the
  output.

Signed-off-by: default avatarQu Wenruo <wqu@suse.com>
Signed-off-by: default avatarDavid Sterba <dsterba@suse.com>
parent 2b83a0ee

fs/btrfs/lzo.c

+134 −136
Original line number Diff line number Diff line
@@ -32,19 +32,19 @@ 
 *     payload.

 *     One regular LZO compressed extent can have one or more segments.

 *     For inlined LZO compressed extent, only one segment is allowed.

 *     One segment represents at most one page of uncompressed data.

 *     One segment represents at most one sector of uncompressed data.

 *

 * 2.1 Segment header

 *     Fixed size. LZO_LEN (4) bytes long, LE32.

 *     Records the total size of the segment (not including the header).

 *     Segment header never crosses page boundary, thus it's possible to

 *     have at most 3 padding zeros at the end of the page.

 *     Segment header never crosses sector boundary, thus it's possible to

 *     have at most 3 padding zeros at the end of the sector.

 *

 * 2.2 Data Payload

 *     Variable size. Size up limit should be lzo1x_worst_compress(PAGE_SIZE)

 *     which is 4419 for a 4KiB page.

 *     Variable size. Size up limit should be lzo1x_worst_compress(sectorsize)

 *     which is 4419 for a 4KiB sectorsize.

 *

 * Example:

 * Example with 4K sectorsize:

 * Page 1:

 *          0     0x2   0x4   0x6   0x8   0xa   0xc   0xe     0x10

 * 0x0000   |  Header   | SegHdr 01 | Data payload 01 ...     |
@@ -112,163 +112,161 @@ static inline size_t read_compress_length(const char *buf) 
	return le32_to_cpu(dlen);

}



int lzo_compress_pages(struct list_head *ws, struct address_space *mapping,

		u64 start, struct page **pages, unsigned long *out_pages,

		unsigned long *total_in, unsigned long *total_out)

/*

 * Will do:

 *

 * - Write a segment header into the destination

 * - Copy the compressed buffer into the destination

 * - Make sure we have enough space in the last sector to fit a segment header

 *   If not, we will pad at most (LZO_LEN (4)) - 1 bytes of zeros.

 *

 * Will allocate new pages when needed.

 */

static int copy_compressed_data_to_page(char *compressed_data,

					size_t compressed_size,

					struct page **out_pages,

					u32 *cur_out,

					const u32 sectorsize)

{

	struct workspace *workspace = list_entry(ws, struct workspace, list);

	int ret = 0;

	char *data_in;

	char *cpage_out, *sizes_ptr;

	int nr_pages = 0;

	struct page *in_page = NULL;

	struct page *out_page = NULL;

	unsigned long bytes_left;

	unsigned long len = *total_out;

	unsigned long nr_dest_pages = *out_pages;

	const unsigned long max_out = nr_dest_pages * PAGE_SIZE;

	size_t in_len;

	size_t out_len;

	char *buf;

	unsigned long tot_in = 0;

	unsigned long tot_out = 0;

	unsigned long pg_bytes_left;

	unsigned long out_offset;

	unsigned long bytes;



	*out_pages = 0;

	*total_out = 0;

	*total_in = 0;



	in_page = find_get_page(mapping, start >> PAGE_SHIFT);

	data_in = page_address(in_page);

	u32 sector_bytes_left;

	u32 orig_out;

	struct page *cur_page;



	/*

	 * store the size of all chunks of compressed data in

	 * the first 4 bytes

	 * We never allow a segment header crossing sector boundary, previous

	 * run should ensure we have enough space left inside the sector.

	 */

	out_page = alloc_page(GFP_NOFS);

	if (out_page == NULL) {

		ret = -ENOMEM;

		goto out;

	}

	cpage_out = page_address(out_page);

	out_offset = LZO_LEN;

	tot_out = LZO_LEN;

	pages[0] = out_page;

	nr_pages = 1;

	pg_bytes_left = PAGE_SIZE - LZO_LEN;



	/* compress at most one page of data each time */

	in_len = min(len, PAGE_SIZE);

	while (tot_in < len) {

		ret = lzo1x_1_compress(data_in, in_len, workspace->cbuf,

				       &out_len, workspace->mem);

		if (ret != LZO_E_OK) {

			pr_debug("BTRFS: lzo in loop returned %d\n",

			       ret);

			ret = -EIO;

			goto out;

	ASSERT((*cur_out / sectorsize) == (*cur_out + LZO_LEN - 1) / sectorsize);



	cur_page = out_pages[*cur_out / PAGE_SIZE];

	/* Allocate a new page */

	if (!cur_page) {

		cur_page = alloc_page(GFP_NOFS);

		if (!cur_page)

			return -ENOMEM;

		out_pages[*cur_out / PAGE_SIZE] = cur_page;

	}



		/* store the size of this chunk of compressed data */

		write_compress_length(cpage_out + out_offset, out_len);

		tot_out += LZO_LEN;

		out_offset += LZO_LEN;

		pg_bytes_left -= LZO_LEN;

	write_compress_length(page_address(cur_page) + offset_in_page(*cur_out),

			      compressed_size);

	*cur_out += LZO_LEN;



	orig_out = *cur_out;



		tot_in += in_len;

		tot_out += out_len;

	/* Copy compressed data */

	while (*cur_out - orig_out < compressed_size) {

		u32 copy_len = min_t(u32, sectorsize - *cur_out % sectorsize,

				     orig_out + compressed_size - *cur_out);



		/* copy bytes from the working buffer into the pages */

		buf = workspace->cbuf;

		while (out_len) {

			bytes = min_t(unsigned long, pg_bytes_left, out_len);

		cur_page = out_pages[*cur_out / PAGE_SIZE];

		/* Allocate a new page */

		if (!cur_page) {

			cur_page = alloc_page(GFP_NOFS);

			if (!cur_page)

				return -ENOMEM;

			out_pages[*cur_out / PAGE_SIZE] = cur_page;

		}



			memcpy(cpage_out + out_offset, buf, bytes);

		memcpy(page_address(cur_page) + offset_in_page(*cur_out),

		       compressed_data + *cur_out - orig_out, copy_len);



			out_len -= bytes;

			pg_bytes_left -= bytes;

			buf += bytes;

			out_offset += bytes;

		*cur_out += copy_len;

	}



	/*

			 * we need another page for writing out.

			 *

			 * Note if there's less than 4 bytes left, we just

			 * skip to a new page.

	 * Check if we can fit the next segment header into the remaining space

	 * of the sector.

	 */

			if ((out_len == 0 && pg_bytes_left < LZO_LEN) ||

			    pg_bytes_left == 0) {

				if (pg_bytes_left) {

					memset(cpage_out + out_offset, 0,

					       pg_bytes_left);

					tot_out += pg_bytes_left;

	sector_bytes_left = round_up(*cur_out, sectorsize) - *cur_out;

	if (sector_bytes_left >= LZO_LEN || sector_bytes_left == 0)

		return 0;



	/* The remaining size is not enough, pad it with zeros */

	memset(page_address(cur_page) + offset_in_page(*cur_out), 0,

	       sector_bytes_left);

	*cur_out += sector_bytes_left;

	return 0;

}



				/* we're done, don't allocate new page */

				if (out_len == 0 && tot_in >= len)

					break;

int lzo_compress_pages(struct list_head *ws, struct address_space *mapping,

		u64 start, struct page **pages, unsigned long *out_pages,

		unsigned long *total_in, unsigned long *total_out)

{

	struct workspace *workspace = list_entry(ws, struct workspace, list);

	const u32 sectorsize = btrfs_sb(mapping->host->i_sb)->sectorsize;

	struct page *page_in = NULL;

	int ret = 0;

	/* Points to the file offset of input data */

	u64 cur_in = start;

	/* Points to the current output byte */

	u32 cur_out = 0;

	u32 len = *total_out;



	*out_pages = 0;

	*total_out = 0;

	*total_in = 0;



				if (nr_pages == nr_dest_pages) {

					out_page = NULL;

					ret = -E2BIG;

					goto out;

	/*

	 * Skip the header for now, we will later come back and write the total

	 * compressed size

	 */

	cur_out += LZO_LEN;

	while (cur_in < start + len) {

		const u32 sectorsize_mask = sectorsize - 1;

		u32 sector_off = (cur_in - start) & sectorsize_mask;

		u32 in_len;

		size_t out_len;



		/* Get the input page first */

		if (!page_in) {

			page_in = find_get_page(mapping, cur_in >> PAGE_SHIFT);

			ASSERT(page_in);

		}



				out_page = alloc_page(GFP_NOFS);

				if (out_page == NULL) {

					ret = -ENOMEM;

		/* Compress at most one sector of data each time */

		in_len = min_t(u32, start + len - cur_in, sectorsize - sector_off);

		ASSERT(in_len);

		ret = lzo1x_1_compress(page_address(page_in) +

				       offset_in_page(cur_in), in_len,

				       workspace->cbuf, &out_len,

				       workspace->mem);

		if (ret < 0) {

			pr_debug("BTRFS: lzo in loop returned %d\n", ret);

			ret = -EIO;

			goto out;

		}

				cpage_out = page_address(out_page);

				pages[nr_pages++] = out_page;



				pg_bytes_left = PAGE_SIZE;

				out_offset = 0;

			}

		}

		ret = copy_compressed_data_to_page(workspace->cbuf, out_len,

						   pages, &cur_out, sectorsize);

		if (ret < 0)

			goto out;



		/* we're making it bigger, give up */

		if (tot_in > 8192 && tot_in < tot_out) {

		cur_in += in_len;



		/*

		 * Check if we're making it bigger after two sectors.  And if

		 * it is so, give up.

		 */

		if (cur_in - start > sectorsize * 2 && cur_in - start < cur_out) {

			ret = -E2BIG;

			goto out;

		}



		/* we're all done */

		if (tot_in >= len)

			break;



		if (tot_out > max_out)

			break;



		bytes_left = len - tot_in;

		put_page(in_page);



		start += PAGE_SIZE;

		in_page = find_get_page(mapping, start >> PAGE_SHIFT);

		data_in = page_address(in_page);

		in_len = min(bytes_left, PAGE_SIZE);

		/* Check if we have reached page boundary */

		if (IS_ALIGNED(cur_in, PAGE_SIZE)) {

			put_page(page_in);

			page_in = NULL;

		}



	if (tot_out >= tot_in) {

		ret = -E2BIG;

		goto out;

	}



	/* store the size of all chunks of compressed data */

	sizes_ptr = page_address(pages[0]);

	write_compress_length(sizes_ptr, tot_out);

	/* Store the size of all chunks of compressed data */

	write_compress_length(page_address(pages[0]), cur_out);



	ret = 0;

	*total_out = tot_out;

	*total_in = tot_in;

	*total_out = cur_out;

	*total_in = cur_in - start;

out:

	*out_pages = nr_pages;



	if (in_page)

		put_page(in_page);



	*out_pages = DIV_ROUND_UP(cur_out, PAGE_SIZE);

	return ret;

}