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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: Qu Wenruo <wqu@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Qu Wenruo
David Sterba
parent
2b83a0eea5
commit
d4088803f5
1 changed files with 132 additions and 134 deletions
266
fs/btrfs/lzo.c
266
fs/btrfs/lzo.c
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@ -32,19 +32,19 @@
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* payload.
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* One regular LZO compressed extent can have one or more segments.
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* For inlined LZO compressed extent, only one segment is allowed.
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* One segment represents at most one page of uncompressed data.
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* One segment represents at most one sector of uncompressed data.
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*
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* 2.1 Segment header
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* Fixed size. LZO_LEN (4) bytes long, LE32.
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* Records the total size of the segment (not including the header).
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* Segment header never crosses page boundary, thus it's possible to
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* have at most 3 padding zeros at the end of the page.
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* Segment header never crosses sector boundary, thus it's possible to
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* have at most 3 padding zeros at the end of the sector.
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*
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* 2.2 Data Payload
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* Variable size. Size up limit should be lzo1x_worst_compress(PAGE_SIZE)
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* which is 4419 for a 4KiB page.
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* Variable size. Size up limit should be lzo1x_worst_compress(sectorsize)
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* which is 4419 for a 4KiB sectorsize.
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*
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* Example:
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* Example with 4K sectorsize:
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* Page 1:
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* 0 0x2 0x4 0x6 0x8 0xa 0xc 0xe 0x10
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* 0x0000 | Header | SegHdr 01 | Data payload 01 ... |
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@ -112,163 +112,161 @@ static inline size_t read_compress_length(const char *buf)
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return le32_to_cpu(dlen);
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}
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/*
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* Will do:
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*
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* - Write a segment header into the destination
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* - Copy the compressed buffer into the destination
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* - Make sure we have enough space in the last sector to fit a segment header
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* If not, we will pad at most (LZO_LEN (4)) - 1 bytes of zeros.
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*
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* Will allocate new pages when needed.
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*/
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static int copy_compressed_data_to_page(char *compressed_data,
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size_t compressed_size,
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struct page **out_pages,
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u32 *cur_out,
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const u32 sectorsize)
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{
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u32 sector_bytes_left;
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u32 orig_out;
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struct page *cur_page;
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/*
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* We never allow a segment header crossing sector boundary, previous
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* run should ensure we have enough space left inside the sector.
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*/
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ASSERT((*cur_out / sectorsize) == (*cur_out + LZO_LEN - 1) / sectorsize);
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cur_page = out_pages[*cur_out / PAGE_SIZE];
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/* Allocate a new page */
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if (!cur_page) {
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cur_page = alloc_page(GFP_NOFS);
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if (!cur_page)
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return -ENOMEM;
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out_pages[*cur_out / PAGE_SIZE] = cur_page;
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}
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write_compress_length(page_address(cur_page) + offset_in_page(*cur_out),
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compressed_size);
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*cur_out += LZO_LEN;
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orig_out = *cur_out;
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/* Copy compressed data */
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while (*cur_out - orig_out < compressed_size) {
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u32 copy_len = min_t(u32, sectorsize - *cur_out % sectorsize,
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orig_out + compressed_size - *cur_out);
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cur_page = out_pages[*cur_out / PAGE_SIZE];
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/* Allocate a new page */
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if (!cur_page) {
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cur_page = alloc_page(GFP_NOFS);
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if (!cur_page)
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return -ENOMEM;
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out_pages[*cur_out / PAGE_SIZE] = cur_page;
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}
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memcpy(page_address(cur_page) + offset_in_page(*cur_out),
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compressed_data + *cur_out - orig_out, copy_len);
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*cur_out += copy_len;
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}
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/*
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* Check if we can fit the next segment header into the remaining space
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* of the sector.
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*/
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sector_bytes_left = round_up(*cur_out, sectorsize) - *cur_out;
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if (sector_bytes_left >= LZO_LEN || sector_bytes_left == 0)
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return 0;
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/* The remaining size is not enough, pad it with zeros */
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memset(page_address(cur_page) + offset_in_page(*cur_out), 0,
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sector_bytes_left);
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*cur_out += sector_bytes_left;
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return 0;
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}
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int lzo_compress_pages(struct list_head *ws, struct address_space *mapping,
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u64 start, struct page **pages, unsigned long *out_pages,
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unsigned long *total_in, unsigned long *total_out)
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{
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struct workspace *workspace = list_entry(ws, struct workspace, list);
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const u32 sectorsize = btrfs_sb(mapping->host->i_sb)->sectorsize;
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struct page *page_in = NULL;
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int ret = 0;
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char *data_in;
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char *cpage_out, *sizes_ptr;
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int nr_pages = 0;
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struct page *in_page = NULL;
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struct page *out_page = NULL;
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unsigned long bytes_left;
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unsigned long len = *total_out;
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unsigned long nr_dest_pages = *out_pages;
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const unsigned long max_out = nr_dest_pages * PAGE_SIZE;
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size_t in_len;
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size_t out_len;
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char *buf;
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unsigned long tot_in = 0;
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unsigned long tot_out = 0;
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unsigned long pg_bytes_left;
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unsigned long out_offset;
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unsigned long bytes;
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/* Points to the file offset of input data */
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u64 cur_in = start;
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/* Points to the current output byte */
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u32 cur_out = 0;
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u32 len = *total_out;
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*out_pages = 0;
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*total_out = 0;
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*total_in = 0;
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in_page = find_get_page(mapping, start >> PAGE_SHIFT);
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data_in = page_address(in_page);
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/*
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* store the size of all chunks of compressed data in
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* the first 4 bytes
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* Skip the header for now, we will later come back and write the total
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* compressed size
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*/
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out_page = alloc_page(GFP_NOFS);
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if (out_page == NULL) {
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ret = -ENOMEM;
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goto out;
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}
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cpage_out = page_address(out_page);
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out_offset = LZO_LEN;
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tot_out = LZO_LEN;
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pages[0] = out_page;
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nr_pages = 1;
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pg_bytes_left = PAGE_SIZE - LZO_LEN;
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cur_out += LZO_LEN;
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while (cur_in < start + len) {
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const u32 sectorsize_mask = sectorsize - 1;
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u32 sector_off = (cur_in - start) & sectorsize_mask;
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u32 in_len;
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size_t out_len;
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/* compress at most one page of data each time */
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in_len = min(len, PAGE_SIZE);
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while (tot_in < len) {
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ret = lzo1x_1_compress(data_in, in_len, workspace->cbuf,
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&out_len, workspace->mem);
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if (ret != LZO_E_OK) {
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pr_debug("BTRFS: lzo in loop returned %d\n",
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ret);
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/* Get the input page first */
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if (!page_in) {
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page_in = find_get_page(mapping, cur_in >> PAGE_SHIFT);
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ASSERT(page_in);
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}
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/* Compress at most one sector of data each time */
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in_len = min_t(u32, start + len - cur_in, sectorsize - sector_off);
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ASSERT(in_len);
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ret = lzo1x_1_compress(page_address(page_in) +
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offset_in_page(cur_in), in_len,
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workspace->cbuf, &out_len,
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workspace->mem);
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if (ret < 0) {
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pr_debug("BTRFS: lzo in loop returned %d\n", ret);
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ret = -EIO;
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goto out;
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}
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/* store the size of this chunk of compressed data */
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write_compress_length(cpage_out + out_offset, out_len);
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tot_out += LZO_LEN;
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out_offset += LZO_LEN;
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pg_bytes_left -= LZO_LEN;
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ret = copy_compressed_data_to_page(workspace->cbuf, out_len,
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pages, &cur_out, sectorsize);
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if (ret < 0)
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goto out;
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tot_in += in_len;
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tot_out += out_len;
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cur_in += in_len;
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/* copy bytes from the working buffer into the pages */
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buf = workspace->cbuf;
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while (out_len) {
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bytes = min_t(unsigned long, pg_bytes_left, out_len);
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memcpy(cpage_out + out_offset, buf, bytes);
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out_len -= bytes;
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pg_bytes_left -= bytes;
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buf += bytes;
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out_offset += bytes;
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/*
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* we need another page for writing out.
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*
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* Note if there's less than 4 bytes left, we just
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* skip to a new page.
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*/
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if ((out_len == 0 && pg_bytes_left < LZO_LEN) ||
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pg_bytes_left == 0) {
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if (pg_bytes_left) {
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memset(cpage_out + out_offset, 0,
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pg_bytes_left);
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tot_out += pg_bytes_left;
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}
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/* we're done, don't allocate new page */
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if (out_len == 0 && tot_in >= len)
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break;
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if (nr_pages == nr_dest_pages) {
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out_page = NULL;
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ret = -E2BIG;
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goto out;
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}
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out_page = alloc_page(GFP_NOFS);
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if (out_page == NULL) {
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ret = -ENOMEM;
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goto out;
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}
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cpage_out = page_address(out_page);
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pages[nr_pages++] = out_page;
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pg_bytes_left = PAGE_SIZE;
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out_offset = 0;
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}
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}
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/* we're making it bigger, give up */
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if (tot_in > 8192 && tot_in < tot_out) {
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/*
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* Check if we're making it bigger after two sectors. And if
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* it is so, give up.
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*/
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if (cur_in - start > sectorsize * 2 && cur_in - start < cur_out) {
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ret = -E2BIG;
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goto out;
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}
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/* we're all done */
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if (tot_in >= len)
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break;
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if (tot_out > max_out)
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break;
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bytes_left = len - tot_in;
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put_page(in_page);
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start += PAGE_SIZE;
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in_page = find_get_page(mapping, start >> PAGE_SHIFT);
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data_in = page_address(in_page);
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in_len = min(bytes_left, PAGE_SIZE);
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/* Check if we have reached page boundary */
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if (IS_ALIGNED(cur_in, PAGE_SIZE)) {
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put_page(page_in);
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page_in = NULL;
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}
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}
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if (tot_out >= tot_in) {
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ret = -E2BIG;
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goto out;
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}
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/* store the size of all chunks of compressed data */
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sizes_ptr = page_address(pages[0]);
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write_compress_length(sizes_ptr, tot_out);
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/* Store the size of all chunks of compressed data */
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write_compress_length(page_address(pages[0]), cur_out);
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ret = 0;
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*total_out = tot_out;
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*total_in = tot_in;
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*total_out = cur_out;
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*total_in = cur_in - start;
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out:
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*out_pages = nr_pages;
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if (in_page)
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put_page(in_page);
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*out_pages = DIV_ROUND_UP(cur_out, PAGE_SIZE);
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return ret;
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}
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