diff options
Diffstat (limited to 'fs/btrfs/compression.c')
| -rw-r--r-- | fs/btrfs/compression.c | 1732 |
1 files changed, 1732 insertions, 0 deletions
diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c new file mode 100644 index 000000000..646416b59 --- /dev/null +++ b/fs/btrfs/compression.c @@ -0,0 +1,1732 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Copyright (C) 2008 Oracle. All rights reserved. + */ + +#include <linux/kernel.h> +#include <linux/bio.h> +#include <linux/file.h> +#include <linux/fs.h> +#include <linux/pagemap.h> +#include <linux/highmem.h> +#include <linux/time.h> +#include <linux/init.h> +#include <linux/string.h> +#include <linux/backing-dev.h> +#include <linux/writeback.h> +#include <linux/slab.h> +#include <linux/sched/mm.h> +#include <linux/log2.h> +#include <crypto/hash.h> +#include "misc.h" +#include "ctree.h" +#include "disk-io.h" +#include "transaction.h" +#include "btrfs_inode.h" +#include "volumes.h" +#include "ordered-data.h" +#include "compression.h" +#include "extent_io.h" +#include "extent_map.h" + +static const char* const btrfs_compress_types[] = { "", "zlib", "lzo", "zstd" }; + +const char* btrfs_compress_type2str(enum btrfs_compression_type type) +{ + switch (type) { + case BTRFS_COMPRESS_ZLIB: + case BTRFS_COMPRESS_LZO: + case BTRFS_COMPRESS_ZSTD: + case BTRFS_COMPRESS_NONE: + return btrfs_compress_types[type]; + default: + break; + } + + return NULL; +} + +bool btrfs_compress_is_valid_type(const char *str, size_t len) +{ + int i; + + for (i = 1; i < ARRAY_SIZE(btrfs_compress_types); i++) { + size_t comp_len = strlen(btrfs_compress_types[i]); + + if (len < comp_len) + continue; + + if (!strncmp(btrfs_compress_types[i], str, comp_len)) + return true; + } + return false; +} + +static int compression_compress_pages(int type, 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) +{ + switch (type) { + case BTRFS_COMPRESS_ZLIB: + return zlib_compress_pages(ws, mapping, start, pages, + out_pages, total_in, total_out); + case BTRFS_COMPRESS_LZO: + return lzo_compress_pages(ws, mapping, start, pages, + out_pages, total_in, total_out); + case BTRFS_COMPRESS_ZSTD: + return zstd_compress_pages(ws, mapping, start, pages, + out_pages, total_in, total_out); + case BTRFS_COMPRESS_NONE: + default: + /* + * This can happen when compression races with remount setting + * it to 'no compress', while caller doesn't call + * inode_need_compress() to check if we really need to + * compress. + * + * Not a big deal, just need to inform caller that we + * haven't allocated any pages yet. + */ + *out_pages = 0; + return -E2BIG; + } +} + +static int compression_decompress_bio(int type, struct list_head *ws, + struct compressed_bio *cb) +{ + switch (type) { + case BTRFS_COMPRESS_ZLIB: return zlib_decompress_bio(ws, cb); + case BTRFS_COMPRESS_LZO: return lzo_decompress_bio(ws, cb); + case BTRFS_COMPRESS_ZSTD: return zstd_decompress_bio(ws, cb); + case BTRFS_COMPRESS_NONE: + default: + /* + * This can't happen, the type is validated several times + * before we get here. + */ + BUG(); + } +} + +static int compression_decompress(int type, struct list_head *ws, + unsigned char *data_in, struct page *dest_page, + unsigned long start_byte, size_t srclen, size_t destlen) +{ + switch (type) { + case BTRFS_COMPRESS_ZLIB: return zlib_decompress(ws, data_in, dest_page, + start_byte, srclen, destlen); + case BTRFS_COMPRESS_LZO: return lzo_decompress(ws, data_in, dest_page, + start_byte, srclen, destlen); + case BTRFS_COMPRESS_ZSTD: return zstd_decompress(ws, data_in, dest_page, + start_byte, srclen, destlen); + case BTRFS_COMPRESS_NONE: + default: + /* + * This can't happen, the type is validated several times + * before we get here. + */ + BUG(); + } +} + +static int btrfs_decompress_bio(struct compressed_bio *cb); + +static inline int compressed_bio_size(struct btrfs_fs_info *fs_info, + unsigned long disk_size) +{ + u16 csum_size = btrfs_super_csum_size(fs_info->super_copy); + + return sizeof(struct compressed_bio) + + (DIV_ROUND_UP(disk_size, fs_info->sectorsize)) * csum_size; +} + +static int check_compressed_csum(struct btrfs_inode *inode, struct bio *bio, + u64 disk_start) +{ + struct btrfs_fs_info *fs_info = inode->root->fs_info; + SHASH_DESC_ON_STACK(shash, fs_info->csum_shash); + const u16 csum_size = btrfs_super_csum_size(fs_info->super_copy); + struct page *page; + unsigned long i; + char *kaddr; + u8 csum[BTRFS_CSUM_SIZE]; + struct compressed_bio *cb = bio->bi_private; + u8 *cb_sum = cb->sums; + + if (inode->flags & BTRFS_INODE_NODATASUM) + return 0; + + shash->tfm = fs_info->csum_shash; + + for (i = 0; i < cb->nr_pages; i++) { + page = cb->compressed_pages[i]; + + kaddr = kmap_atomic(page); + crypto_shash_digest(shash, kaddr, PAGE_SIZE, csum); + kunmap_atomic(kaddr); + + if (memcmp(&csum, cb_sum, csum_size)) { + btrfs_print_data_csum_error(inode, disk_start, + csum, cb_sum, cb->mirror_num); + if (btrfs_io_bio(bio)->device) + btrfs_dev_stat_inc_and_print( + btrfs_io_bio(bio)->device, + BTRFS_DEV_STAT_CORRUPTION_ERRS); + return -EIO; + } + cb_sum += csum_size; + } + return 0; +} + +/* when we finish reading compressed pages from the disk, we + * decompress them and then run the bio end_io routines on the + * decompressed pages (in the inode address space). + * + * This allows the checksumming and other IO error handling routines + * to work normally + * + * The compressed pages are freed here, and it must be run + * in process context + */ +static void end_compressed_bio_read(struct bio *bio) +{ + struct compressed_bio *cb = bio->bi_private; + struct inode *inode; + struct page *page; + unsigned long index; + unsigned int mirror = btrfs_io_bio(bio)->mirror_num; + int ret = 0; + + if (bio->bi_status) + cb->errors = 1; + + /* if there are more bios still pending for this compressed + * extent, just exit + */ + if (!refcount_dec_and_test(&cb->pending_bios)) + goto out; + + /* + * Record the correct mirror_num in cb->orig_bio so that + * read-repair can work properly. + */ + btrfs_io_bio(cb->orig_bio)->mirror_num = mirror; + cb->mirror_num = mirror; + + /* + * Some IO in this cb have failed, just skip checksum as there + * is no way it could be correct. + */ + if (cb->errors == 1) + goto csum_failed; + + inode = cb->inode; + ret = check_compressed_csum(BTRFS_I(inode), bio, + (u64)bio->bi_iter.bi_sector << 9); + if (ret) + goto csum_failed; + + /* ok, we're the last bio for this extent, lets start + * the decompression. + */ + ret = btrfs_decompress_bio(cb); + +csum_failed: + if (ret) + cb->errors = 1; + + /* release the compressed pages */ + index = 0; + for (index = 0; index < cb->nr_pages; index++) { + page = cb->compressed_pages[index]; + page->mapping = NULL; + put_page(page); + } + + /* do io completion on the original bio */ + if (cb->errors) { + bio_io_error(cb->orig_bio); + } else { + struct bio_vec *bvec; + struct bvec_iter_all iter_all; + + /* + * we have verified the checksum already, set page + * checked so the end_io handlers know about it + */ + ASSERT(!bio_flagged(bio, BIO_CLONED)); + bio_for_each_segment_all(bvec, cb->orig_bio, iter_all) + SetPageChecked(bvec->bv_page); + + bio_endio(cb->orig_bio); + } + + /* finally free the cb struct */ + kfree(cb->compressed_pages); + kfree(cb); +out: + bio_put(bio); +} + +/* + * Clear the writeback bits on all of the file + * pages for a compressed write + */ +static noinline void end_compressed_writeback(struct inode *inode, + const struct compressed_bio *cb) +{ + unsigned long index = cb->start >> PAGE_SHIFT; + unsigned long end_index = (cb->start + cb->len - 1) >> PAGE_SHIFT; + struct page *pages[16]; + unsigned long nr_pages = end_index - index + 1; + int i; + int ret; + + if (cb->errors) + mapping_set_error(inode->i_mapping, -EIO); + + while (nr_pages > 0) { + ret = find_get_pages_contig(inode->i_mapping, index, + min_t(unsigned long, + nr_pages, ARRAY_SIZE(pages)), pages); + if (ret == 0) { + nr_pages -= 1; + index += 1; + continue; + } + for (i = 0; i < ret; i++) { + if (cb->errors) + SetPageError(pages[i]); + end_page_writeback(pages[i]); + put_page(pages[i]); + } + nr_pages -= ret; + index += ret; + } + /* the inode may be gone now */ +} + +/* + * do the cleanup once all the compressed pages hit the disk. + * This will clear writeback on the file pages and free the compressed + * pages. + * + * This also calls the writeback end hooks for the file pages so that + * metadata and checksums can be updated in the file. + */ +static void end_compressed_bio_write(struct bio *bio) +{ + struct compressed_bio *cb = bio->bi_private; + struct inode *inode; + struct page *page; + unsigned long index; + + if (bio->bi_status) + cb->errors = 1; + + /* if there are more bios still pending for this compressed + * extent, just exit + */ + if (!refcount_dec_and_test(&cb->pending_bios)) + goto out; + + /* ok, we're the last bio for this extent, step one is to + * call back into the FS and do all the end_io operations + */ + inode = cb->inode; + cb->compressed_pages[0]->mapping = cb->inode->i_mapping; + btrfs_writepage_endio_finish_ordered(cb->compressed_pages[0], + cb->start, cb->start + cb->len - 1, + !cb->errors); + cb->compressed_pages[0]->mapping = NULL; + + end_compressed_writeback(inode, cb); + /* note, our inode could be gone now */ + + /* + * release the compressed pages, these came from alloc_page and + * are not attached to the inode at all + */ + index = 0; + for (index = 0; index < cb->nr_pages; index++) { + page = cb->compressed_pages[index]; + page->mapping = NULL; + put_page(page); + } + + /* finally free the cb struct */ + kfree(cb->compressed_pages); + kfree(cb); +out: + bio_put(bio); +} + +/* + * worker function to build and submit bios for previously compressed pages. + * The corresponding pages in the inode should be marked for writeback + * and the compressed pages should have a reference on them for dropping + * when the IO is complete. + * + * This also checksums the file bytes and gets things ready for + * the end io hooks. + */ +blk_status_t btrfs_submit_compressed_write(struct btrfs_inode *inode, u64 start, + unsigned long len, u64 disk_start, + unsigned long compressed_len, + struct page **compressed_pages, + unsigned long nr_pages, + unsigned int write_flags, + struct cgroup_subsys_state *blkcg_css) +{ + struct btrfs_fs_info *fs_info = inode->root->fs_info; + struct bio *bio = NULL; + struct compressed_bio *cb; + unsigned long bytes_left; + int pg_index = 0; + struct page *page; + u64 first_byte = disk_start; + blk_status_t ret; + int skip_sum = inode->flags & BTRFS_INODE_NODATASUM; + + WARN_ON(!PAGE_ALIGNED(start)); + cb = kmalloc(compressed_bio_size(fs_info, compressed_len), GFP_NOFS); + if (!cb) + return BLK_STS_RESOURCE; + refcount_set(&cb->pending_bios, 0); + cb->errors = 0; + cb->inode = &inode->vfs_inode; + cb->start = start; + cb->len = len; + cb->mirror_num = 0; + cb->compressed_pages = compressed_pages; + cb->compressed_len = compressed_len; + cb->orig_bio = NULL; + cb->nr_pages = nr_pages; + + bio = btrfs_bio_alloc(first_byte); + bio->bi_opf = REQ_OP_WRITE | write_flags; + bio->bi_private = cb; + bio->bi_end_io = end_compressed_bio_write; + + if (blkcg_css) { + bio->bi_opf |= REQ_CGROUP_PUNT; + kthread_associate_blkcg(blkcg_css); + } + refcount_set(&cb->pending_bios, 1); + + /* create and submit bios for the compressed pages */ + bytes_left = compressed_len; + for (pg_index = 0; pg_index < cb->nr_pages; pg_index++) { + int submit = 0; + + page = compressed_pages[pg_index]; + page->mapping = inode->vfs_inode.i_mapping; + if (bio->bi_iter.bi_size) + submit = btrfs_bio_fits_in_stripe(page, PAGE_SIZE, bio, + 0); + + page->mapping = NULL; + if (submit || bio_add_page(bio, page, PAGE_SIZE, 0) < + PAGE_SIZE) { + /* + * inc the count before we submit the bio so + * we know the end IO handler won't happen before + * we inc the count. Otherwise, the cb might get + * freed before we're done setting it up + */ + refcount_inc(&cb->pending_bios); + ret = btrfs_bio_wq_end_io(fs_info, bio, + BTRFS_WQ_ENDIO_DATA); + BUG_ON(ret); /* -ENOMEM */ + + if (!skip_sum) { + ret = btrfs_csum_one_bio(inode, bio, start, 1); + BUG_ON(ret); /* -ENOMEM */ + } + + ret = btrfs_map_bio(fs_info, bio, 0); + if (ret) { + bio->bi_status = ret; + bio_endio(bio); + } + + bio = btrfs_bio_alloc(first_byte); + bio->bi_opf = REQ_OP_WRITE | write_flags; + bio->bi_private = cb; + bio->bi_end_io = end_compressed_bio_write; + if (blkcg_css) + bio->bi_opf |= REQ_CGROUP_PUNT; + bio_add_page(bio, page, PAGE_SIZE, 0); + } + if (bytes_left < PAGE_SIZE) { + btrfs_info(fs_info, + "bytes left %lu compress len %lu nr %lu", + bytes_left, cb->compressed_len, cb->nr_pages); + } + bytes_left -= PAGE_SIZE; + first_byte += PAGE_SIZE; + cond_resched(); + } + + ret = btrfs_bio_wq_end_io(fs_info, bio, BTRFS_WQ_ENDIO_DATA); + BUG_ON(ret); /* -ENOMEM */ + + if (!skip_sum) { + ret = btrfs_csum_one_bio(inode, bio, start, 1); + BUG_ON(ret); /* -ENOMEM */ + } + + ret = btrfs_map_bio(fs_info, bio, 0); + if (ret) { + bio->bi_status = ret; + bio_endio(bio); + } + + if (blkcg_css) + kthread_associate_blkcg(NULL); + + return 0; +} + +static u64 bio_end_offset(struct bio *bio) +{ + struct bio_vec *last = bio_last_bvec_all(bio); + + return page_offset(last->bv_page) + last->bv_len + last->bv_offset; +} + +static noinline int add_ra_bio_pages(struct inode *inode, + u64 compressed_end, + struct compressed_bio *cb) +{ + unsigned long end_index; + unsigned long pg_index; + u64 last_offset; + u64 isize = i_size_read(inode); + int ret; + struct page *page; + unsigned long nr_pages = 0; + struct extent_map *em; + struct address_space *mapping = inode->i_mapping; + struct extent_map_tree *em_tree; + struct extent_io_tree *tree; + u64 end; + int misses = 0; + + last_offset = bio_end_offset(cb->orig_bio); + em_tree = &BTRFS_I(inode)->extent_tree; + tree = &BTRFS_I(inode)->io_tree; + + if (isize == 0) + return 0; + + end_index = (i_size_read(inode) - 1) >> PAGE_SHIFT; + + while (last_offset < compressed_end) { + pg_index = last_offset >> PAGE_SHIFT; + + if (pg_index > end_index) + break; + + page = xa_load(&mapping->i_pages, pg_index); + if (page && !xa_is_value(page)) { + misses++; + if (misses > 4) + break; + goto next; + } + + page = __page_cache_alloc(mapping_gfp_constraint(mapping, + ~__GFP_FS)); + if (!page) + break; + + if (add_to_page_cache_lru(page, mapping, pg_index, GFP_NOFS)) { + put_page(page); + goto next; + } + + end = last_offset + PAGE_SIZE - 1; + /* + * at this point, we have a locked page in the page cache + * for these bytes in the file. But, we have to make + * sure they map to this compressed extent on disk. + */ + set_page_extent_mapped(page); + lock_extent(tree, last_offset, end); + read_lock(&em_tree->lock); + em = lookup_extent_mapping(em_tree, last_offset, + PAGE_SIZE); + read_unlock(&em_tree->lock); + + if (!em || last_offset < em->start || + (last_offset + PAGE_SIZE > extent_map_end(em)) || + (em->block_start >> 9) != cb->orig_bio->bi_iter.bi_sector) { + free_extent_map(em); + unlock_extent(tree, last_offset, end); + unlock_page(page); + put_page(page); + break; + } + free_extent_map(em); + + if (page->index == end_index) { + char *userpage; + size_t zero_offset = offset_in_page(isize); + + if (zero_offset) { + int zeros; + zeros = PAGE_SIZE - zero_offset; + userpage = kmap_atomic(page); + memset(userpage + zero_offset, 0, zeros); + flush_dcache_page(page); + kunmap_atomic(userpage); + } + } + + ret = bio_add_page(cb->orig_bio, page, + PAGE_SIZE, 0); + + if (ret == PAGE_SIZE) { + nr_pages++; + put_page(page); + } else { + unlock_extent(tree, last_offset, end); + unlock_page(page); + put_page(page); + break; + } +next: + last_offset += PAGE_SIZE; + } + return 0; +} + +/* + * for a compressed read, the bio we get passed has all the inode pages + * in it. We don't actually do IO on those pages but allocate new ones + * to hold the compressed pages on disk. + * + * bio->bi_iter.bi_sector points to the compressed extent on disk + * bio->bi_io_vec points to all of the inode pages + * + * After the compressed pages are read, we copy the bytes into the + * bio we were passed and then call the bio end_io calls + */ +blk_status_t btrfs_submit_compressed_read(struct inode *inode, struct bio *bio, + int mirror_num, unsigned long bio_flags) +{ + struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb); + struct extent_map_tree *em_tree; + struct compressed_bio *cb; + unsigned long compressed_len; + unsigned long nr_pages; + unsigned long pg_index; + struct page *page; + struct bio *comp_bio; + u64 cur_disk_byte = (u64)bio->bi_iter.bi_sector << 9; + u64 em_len; + u64 em_start; + struct extent_map *em; + blk_status_t ret = BLK_STS_RESOURCE; + int faili = 0; + const u16 csum_size = btrfs_super_csum_size(fs_info->super_copy); + u8 *sums; + + em_tree = &BTRFS_I(inode)->extent_tree; + + /* we need the actual starting offset of this extent in the file */ + read_lock(&em_tree->lock); + em = lookup_extent_mapping(em_tree, + page_offset(bio_first_page_all(bio)), + PAGE_SIZE); + read_unlock(&em_tree->lock); + if (!em) + return BLK_STS_IOERR; + + compressed_len = em->block_len; + cb = kmalloc(compressed_bio_size(fs_info, compressed_len), GFP_NOFS); + if (!cb) + goto out; + + refcount_set(&cb->pending_bios, 0); + cb->errors = 0; + cb->inode = inode; + cb->mirror_num = mirror_num; + sums = cb->sums; + + cb->start = em->orig_start; + em_len = em->len; + em_start = em->start; + + free_extent_map(em); + em = NULL; + + cb->len = bio->bi_iter.bi_size; + cb->compressed_len = compressed_len; + cb->compress_type = extent_compress_type(bio_flags); + cb->orig_bio = bio; + + nr_pages = DIV_ROUND_UP(compressed_len, PAGE_SIZE); + cb->compressed_pages = kcalloc(nr_pages, sizeof(struct page *), + GFP_NOFS); + if (!cb->compressed_pages) + goto fail1; + + for (pg_index = 0; pg_index < nr_pages; pg_index++) { + cb->compressed_pages[pg_index] = alloc_page(GFP_NOFS | + __GFP_HIGHMEM); + if (!cb->compressed_pages[pg_index]) { + faili = pg_index - 1; + ret = BLK_STS_RESOURCE; + goto fail2; + } + } + faili = nr_pages - 1; + cb->nr_pages = nr_pages; + + add_ra_bio_pages(inode, em_start + em_len, cb); + + /* include any pages we added in add_ra-bio_pages */ + cb->len = bio->bi_iter.bi_size; + + comp_bio = btrfs_bio_alloc(cur_disk_byte); + comp_bio->bi_opf = REQ_OP_READ; + comp_bio->bi_private = cb; + comp_bio->bi_end_io = end_compressed_bio_read; + refcount_set(&cb->pending_bios, 1); + + for (pg_index = 0; pg_index < nr_pages; pg_index++) { + int submit = 0; + + page = cb->compressed_pages[pg_index]; + page->mapping = inode->i_mapping; + page->index = em_start >> PAGE_SHIFT; + + if (comp_bio->bi_iter.bi_size) + submit = btrfs_bio_fits_in_stripe(page, PAGE_SIZE, + comp_bio, 0); + + page->mapping = NULL; + if (submit || bio_add_page(comp_bio, page, PAGE_SIZE, 0) < + PAGE_SIZE) { + unsigned int nr_sectors; + + ret = btrfs_bio_wq_end_io(fs_info, comp_bio, + BTRFS_WQ_ENDIO_DATA); + BUG_ON(ret); /* -ENOMEM */ + + /* + * inc the count before we submit the bio so + * we know the end IO handler won't happen before + * we inc the count. Otherwise, the cb might get + * freed before we're done setting it up + */ + refcount_inc(&cb->pending_bios); + + if (!(BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM)) { + ret = btrfs_lookup_bio_sums(inode, comp_bio, + (u64)-1, sums); + BUG_ON(ret); /* -ENOMEM */ + } + + nr_sectors = DIV_ROUND_UP(comp_bio->bi_iter.bi_size, + fs_info->sectorsize); + sums += csum_size * nr_sectors; + + ret = btrfs_map_bio(fs_info, comp_bio, mirror_num); + if (ret) { + comp_bio->bi_status = ret; + bio_endio(comp_bio); + } + + comp_bio = btrfs_bio_alloc(cur_disk_byte); + comp_bio->bi_opf = REQ_OP_READ; + comp_bio->bi_private = cb; + comp_bio->bi_end_io = end_compressed_bio_read; + + bio_add_page(comp_bio, page, PAGE_SIZE, 0); + } + cur_disk_byte += PAGE_SIZE; + } + + ret = btrfs_bio_wq_end_io(fs_info, comp_bio, BTRFS_WQ_ENDIO_DATA); + BUG_ON(ret); /* -ENOMEM */ + + if (!(BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM)) { + ret = btrfs_lookup_bio_sums(inode, comp_bio, (u64)-1, sums); + BUG_ON(ret); /* -ENOMEM */ + } + + ret = btrfs_map_bio(fs_info, comp_bio, mirror_num); + if (ret) { + comp_bio->bi_status = ret; + bio_endio(comp_bio); + } + + return 0; + +fail2: + while (faili >= 0) { + __free_page(cb->compressed_pages[faili]); + faili--; + } + + kfree(cb->compressed_pages); +fail1: + kfree(cb); +out: + free_extent_map(em); + return ret; +} + +/* + * Heuristic uses systematic sampling to collect data from the input data + * range, the logic can be tuned by the following constants: + * + * @SAMPLING_READ_SIZE - how many bytes will be copied from for each sample + * @SAMPLING_INTERVAL - range from which the sampled data can be collected + */ +#define SAMPLING_READ_SIZE (16) +#define SAMPLING_INTERVAL (256) + +/* + * For statistical analysis of the input data we consider bytes that form a + * Galois Field of 256 objects. Each object has an attribute count, ie. how + * many times the object appeared in the sample. + */ +#define BUCKET_SIZE (256) + +/* + * The size of the sample is based on a statistical sampling rule of thumb. + * The common way is to perform sampling tests as long as the number of + * elements in each cell is at least 5. + * + * Instead of 5, we choose 32 to obtain more accurate results. + * If the data contain the maximum number of symbols, which is 256, we obtain a + * sample size bound by 8192. + * + * For a sample of at most 8KB of data per data range: 16 consecutive bytes + * from up to 512 locations. + */ +#define MAX_SAMPLE_SIZE (BTRFS_MAX_UNCOMPRESSED * \ + SAMPLING_READ_SIZE / SAMPLING_INTERVAL) + +struct bucket_item { + u32 count; +}; + +struct heuristic_ws { + /* Partial copy of input data */ + u8 *sample; + u32 sample_size; + /* Buckets store counters for each byte value */ + struct bucket_item *bucket; + /* Sorting buffer */ + struct bucket_item *bucket_b; + struct list_head list; +}; + +static struct workspace_manager heuristic_wsm; + +static void free_heuristic_ws(struct list_head *ws) +{ + struct heuristic_ws *workspace; + + workspace = list_entry(ws, struct heuristic_ws, list); + + kvfree(workspace->sample); + kfree(workspace->bucket); + kfree(workspace->bucket_b); + kfree(workspace); +} + +static struct list_head *alloc_heuristic_ws(unsigned int level) +{ + struct heuristic_ws *ws; + + ws = kzalloc(sizeof(*ws), GFP_KERNEL); + if (!ws) + return ERR_PTR(-ENOMEM); + + ws->sample = kvmalloc(MAX_SAMPLE_SIZE, GFP_KERNEL); + if (!ws->sample) + goto fail; + + ws->bucket = kcalloc(BUCKET_SIZE, sizeof(*ws->bucket), GFP_KERNEL); + if (!ws->bucket) + goto fail; + + ws->bucket_b = kcalloc(BUCKET_SIZE, sizeof(*ws->bucket_b), GFP_KERNEL); + if (!ws->bucket_b) + goto fail; + + INIT_LIST_HEAD(&ws->list); + return &ws->list; +fail: + free_heuristic_ws(&ws->list); + return ERR_PTR(-ENOMEM); +} + +const struct btrfs_compress_op btrfs_heuristic_compress = { + .workspace_manager = &heuristic_wsm, +}; + +static const struct btrfs_compress_op * const btrfs_compress_op[] = { + /* The heuristic is represented as compression type 0 */ + &btrfs_heuristic_compress, + &btrfs_zlib_compress, + &btrfs_lzo_compress, + &btrfs_zstd_compress, +}; + +static struct list_head *alloc_workspace(int type, unsigned int level) +{ + switch (type) { + case BTRFS_COMPRESS_NONE: return alloc_heuristic_ws(level); + case BTRFS_COMPRESS_ZLIB: return zlib_alloc_workspace(level); + case BTRFS_COMPRESS_LZO: return lzo_alloc_workspace(level); + case BTRFS_COMPRESS_ZSTD: return zstd_alloc_workspace(level); + default: + /* + * This can't happen, the type is validated several times + * before we get here. + */ + BUG(); + } +} + +static void free_workspace(int type, struct list_head *ws) +{ + switch (type) { + case BTRFS_COMPRESS_NONE: return free_heuristic_ws(ws); + case BTRFS_COMPRESS_ZLIB: return zlib_free_workspace(ws); + case BTRFS_COMPRESS_LZO: return lzo_free_workspace(ws); + case BTRFS_COMPRESS_ZSTD: return zstd_free_workspace(ws); + default: + /* + * This can't happen, the type is validated several times + * before we get here. + */ + BUG(); + } +} + +static void btrfs_init_workspace_manager(int type) +{ + struct workspace_manager *wsm; + struct list_head *workspace; + + wsm = btrfs_compress_op[type]->workspace_manager; + INIT_LIST_HEAD(&wsm->idle_ws); + spin_lock_init(&wsm->ws_lock); + atomic_set(&wsm->total_ws, 0); + init_waitqueue_head(&wsm->ws_wait); + + /* + * Preallocate one workspace for each compression type so we can + * guarantee forward progress in the worst case + */ + workspace = alloc_workspace(type, 0); + if (IS_ERR(workspace)) { + pr_warn( + "BTRFS: cannot preallocate compression workspace, will try later\n"); + } else { + atomic_set(&wsm->total_ws, 1); + wsm->free_ws = 1; + list_add(workspace, &wsm->idle_ws); + } +} + +static void btrfs_cleanup_workspace_manager(int type) +{ + struct workspace_manager *wsman; + struct list_head *ws; + + wsman = btrfs_compress_op[type]->workspace_manager; + while (!list_empty(&wsman->idle_ws)) { + ws = wsman->idle_ws.next; + list_del(ws); + free_workspace(type, ws); + atomic_dec(&wsman->total_ws); + } +} + +/* + * This finds an available workspace or allocates a new one. + * If it's not possible to allocate a new one, waits until there's one. + * Preallocation makes a forward progress guarantees and we do not return + * errors. + */ +struct list_head *btrfs_get_workspace(int type, unsigned int level) +{ + struct workspace_manager *wsm; + struct list_head *workspace; + int cpus = num_online_cpus(); + unsigned nofs_flag; + struct list_head *idle_ws; + spinlock_t *ws_lock; + atomic_t *total_ws; + wait_queue_head_t *ws_wait; + int *free_ws; + + wsm = btrfs_compress_op[type]->workspace_manager; + idle_ws = &wsm->idle_ws; + ws_lock = &wsm->ws_lock; + total_ws = &wsm->total_ws; + ws_wait = &wsm->ws_wait; + free_ws = &wsm->free_ws; + +again: + spin_lock(ws_lock); + if (!list_empty(idle_ws)) { + workspace = idle_ws->next; + list_del(workspace); + (*free_ws)--; + spin_unlock(ws_lock); + return workspace; + + } + if (atomic_read(total_ws) > cpus) { + DEFINE_WAIT(wait); + + spin_unlock(ws_lock); + prepare_to_wait(ws_wait, &wait, TASK_UNINTERRUPTIBLE); + if (atomic_read(total_ws) > cpus && !*free_ws) + schedule(); + finish_wait(ws_wait, &wait); + goto again; + } + atomic_inc(total_ws); + spin_unlock(ws_lock); + + /* + * Allocation helpers call vmalloc that can't use GFP_NOFS, so we have + * to turn it off here because we might get called from the restricted + * context of btrfs_compress_bio/btrfs_compress_pages + */ + nofs_flag = memalloc_nofs_save(); + workspace = alloc_workspace(type, level); + memalloc_nofs_restore(nofs_flag); + + if (IS_ERR(workspace)) { + atomic_dec(total_ws); + wake_up(ws_wait); + + /* + * Do not return the error but go back to waiting. There's a + * workspace preallocated for each type and the compression + * time is bounded so we get to a workspace eventually. This + * makes our caller's life easier. + * + * To prevent silent and low-probability deadlocks (when the + * initial preallocation fails), check if there are any + * workspaces at all. + */ + if (atomic_read(total_ws) == 0) { + static DEFINE_RATELIMIT_STATE(_rs, + /* once per minute */ 60 * HZ, + /* no burst */ 1); + + if (__ratelimit(&_rs)) { + pr_warn("BTRFS: no compression workspaces, low memory, retrying\n"); + } + } + goto again; + } + return workspace; +} + +static struct list_head *get_workspace(int type, int level) +{ + switch (type) { + case BTRFS_COMPRESS_NONE: return btrfs_get_workspace(type, level); + case BTRFS_COMPRESS_ZLIB: return zlib_get_workspace(level); + case BTRFS_COMPRESS_LZO: return btrfs_get_workspace(type, level); + case BTRFS_COMPRESS_ZSTD: return zstd_get_workspace(level); + default: + /* + * This can't happen, the type is validated several times + * before we get here. + */ + BUG(); + } +} + +/* + * put a workspace struct back on the list or free it if we have enough + * idle ones sitting around + */ +void btrfs_put_workspace(int type, struct list_head *ws) +{ + struct workspace_manager *wsm; + struct list_head *idle_ws; + spinlock_t *ws_lock; + atomic_t *total_ws; + wait_queue_head_t *ws_wait; + int *free_ws; + + wsm = btrfs_compress_op[type]->workspace_manager; + idle_ws = &wsm->idle_ws; + ws_lock = &wsm->ws_lock; + total_ws = &wsm->total_ws; + ws_wait = &wsm->ws_wait; + free_ws = &wsm->free_ws; + + spin_lock(ws_lock); + if (*free_ws <= num_online_cpus()) { + list_add(ws, idle_ws); + (*free_ws)++; + spin_unlock(ws_lock); + goto wake; + } + spin_unlock(ws_lock); + + free_workspace(type, ws); + atomic_dec(total_ws); +wake: + cond_wake_up(ws_wait); +} + +static void put_workspace(int type, struct list_head *ws) +{ + switch (type) { + case BTRFS_COMPRESS_NONE: return btrfs_put_workspace(type, ws); + case BTRFS_COMPRESS_ZLIB: return btrfs_put_workspace(type, ws); + case BTRFS_COMPRESS_LZO: return btrfs_put_workspace(type, ws); + case BTRFS_COMPRESS_ZSTD: return zstd_put_workspace(ws); + default: + /* + * This can't happen, the type is validated several times + * before we get here. + */ + BUG(); + } +} + +/* + * Adjust @level according to the limits of the compression algorithm or + * fallback to default + */ +static unsigned int btrfs_compress_set_level(int type, unsigned level) +{ + const struct btrfs_compress_op *ops = btrfs_compress_op[type]; + + if (level == 0) + level = ops->default_level; + else + level = min(level, ops->max_level); + + return level; +} + +/* + * Given an address space and start and length, compress the bytes into @pages + * that are allocated on demand. + * + * @type_level is encoded algorithm and level, where level 0 means whatever + * default the algorithm chooses and is opaque here; + * - compression algo are 0-3 + * - the level are bits 4-7 + * + * @out_pages is an in/out parameter, holds maximum number of pages to allocate + * and returns number of actually allocated pages + * + * @total_in is used to return the number of bytes actually read. It + * may be smaller than the input length if we had to exit early because we + * ran out of room in the pages array or because we cross the + * max_out threshold. + * + * @total_out is an in/out parameter, must be set to the input length and will + * be also used to return the total number of compressed bytes + * + * @max_out tells us the max number of bytes that we're allowed to + * stuff into pages + */ +int btrfs_compress_pages(unsigned int type_level, struct address_space *mapping, + u64 start, struct page **pages, + unsigned long *out_pages, + unsigned long *total_in, + unsigned long *total_out) +{ + int type = btrfs_compress_type(type_level); + int level = btrfs_compress_level(type_level); + struct list_head *workspace; + int ret; + + level = btrfs_compress_set_level(type, level); + workspace = get_workspace(type, level); + ret = compression_compress_pages(type, workspace, mapping, start, pages, + out_pages, total_in, total_out); + put_workspace(type, workspace); + return ret; +} + +/* + * pages_in is an array of pages with compressed data. + * + * disk_start is the starting logical offset of this array in the file + * + * orig_bio contains the pages from the file that we want to decompress into + * + * srclen is the number of bytes in pages_in + * + * The basic idea is that we have a bio that was created by readpages. + * The pages in the bio are for the uncompressed data, and they may not + * be contiguous. They all correspond to the range of bytes covered by + * the compressed extent. + */ +static int btrfs_decompress_bio(struct compressed_bio *cb) +{ + struct list_head *workspace; + int ret; + int type = cb->compress_type; + + workspace = get_workspace(type, 0); + ret = compression_decompress_bio(type, workspace, cb); + put_workspace(type, workspace); + + return ret; +} + +/* + * a less complex decompression routine. Our compressed data fits in a + * single page, and we want to read a single page out of it. + * start_byte tells us the offset into the compressed data we're interested in + */ +int btrfs_decompress(int type, unsigned char *data_in, struct page *dest_page, + unsigned long start_byte, size_t srclen, size_t destlen) +{ + struct list_head *workspace; + int ret; + + workspace = get_workspace(type, 0); + ret = compression_decompress(type, workspace, data_in, dest_page, + start_byte, srclen, destlen); + put_workspace(type, workspace); + + return ret; +} + +void __init btrfs_init_compress(void) +{ + btrfs_init_workspace_manager(BTRFS_COMPRESS_NONE); + btrfs_init_workspace_manager(BTRFS_COMPRESS_ZLIB); + btrfs_init_workspace_manager(BTRFS_COMPRESS_LZO); + zstd_init_workspace_manager(); +} + +void __cold btrfs_exit_compress(void) +{ + btrfs_cleanup_workspace_manager(BTRFS_COMPRESS_NONE); + btrfs_cleanup_workspace_manager(BTRFS_COMPRESS_ZLIB); + btrfs_cleanup_workspace_manager(BTRFS_COMPRESS_LZO); + zstd_cleanup_workspace_manager(); +} + +/* + * Copy uncompressed data from working buffer to pages. + * + * buf_start is the byte offset we're of the start of our workspace buffer. + * + * total_out is the last byte of the buffer + */ +int btrfs_decompress_buf2page(const char *buf, unsigned long buf_start, + unsigned long total_out, u64 disk_start, + struct bio *bio) +{ + unsigned long buf_offset; + unsigned long current_buf_start; + unsigned long start_byte; + unsigned long prev_start_byte; + unsigned long working_bytes = total_out - buf_start; + unsigned long bytes; + char *kaddr; + struct bio_vec bvec = bio_iter_iovec(bio, bio->bi_iter); + + /* + * start byte is the first byte of the page we're currently + * copying into relative to the start of the compressed data. + */ + start_byte = page_offset(bvec.bv_page) - disk_start; + + /* we haven't yet hit data corresponding to this page */ + if (total_out <= start_byte) + return 1; + + /* + * the start of the data we care about is offset into + * the middle of our working buffer + */ + if (total_out > start_byte && buf_start < start_byte) { + buf_offset = start_byte - buf_start; + working_bytes -= buf_offset; + } else { + buf_offset = 0; + } + current_buf_start = buf_start; + + /* copy bytes from the working buffer into the pages */ + while (working_bytes > 0) { + bytes = min_t(unsigned long, bvec.bv_len, + PAGE_SIZE - (buf_offset % PAGE_SIZE)); + bytes = min(bytes, working_bytes); + + kaddr = kmap_atomic(bvec.bv_page); + memcpy(kaddr + bvec.bv_offset, buf + buf_offset, bytes); + kunmap_atomic(kaddr); + flush_dcache_page(bvec.bv_page); + + buf_offset += bytes; + working_bytes -= bytes; + current_buf_start += bytes; + + /* check if we need to pick another page */ + bio_advance(bio, bytes); + if (!bio->bi_iter.bi_size) + return 0; + bvec = bio_iter_iovec(bio, bio->bi_iter); + prev_start_byte = start_byte; + start_byte = page_offset(bvec.bv_page) - disk_start; + + /* + * We need to make sure we're only adjusting + * our offset into compression working buffer when + * we're switching pages. Otherwise we can incorrectly + * keep copying when we were actually done. + */ + if (start_byte != prev_start_byte) { + /* + * make sure our new page is covered by this + * working buffer + */ + if (total_out <= start_byte) + return 1; + + /* + * the next page in the biovec might not be adjacent + * to the last page, but it might still be found + * inside this working buffer. bump our offset pointer + */ + if (total_out > start_byte && + current_buf_start < start_byte) { + buf_offset = start_byte - buf_start; + working_bytes = total_out - start_byte; + current_buf_start = buf_start + buf_offset; + } + } + } + + return 1; +} + +/* + * Shannon Entropy calculation + * + * Pure byte distribution analysis fails to determine compressibility of data. + * Try calculating entropy to estimate the average minimum number of bits + * needed to encode the sampled data. + * + * For convenience, return the percentage of needed bits, instead of amount of + * bits directly. + * + * @ENTROPY_LVL_ACEPTABLE - below that threshold, sample has low byte entropy + * and can be compressible with high probability + * + * @ENTROPY_LVL_HIGH - data are not compressible with high probability + * + * Use of ilog2() decreases precision, we lower the LVL to 5 to compensate. + */ +#define ENTROPY_LVL_ACEPTABLE (65) +#define ENTROPY_LVL_HIGH (80) + +/* + * For increasead precision in shannon_entropy calculation, + * let's do pow(n, M) to save more digits after comma: + * + * - maximum int bit length is 64 + * - ilog2(MAX_SAMPLE_SIZE) -> 13 + * - 13 * 4 = 52 < 64 -> M = 4 + * + * So use pow(n, 4). + */ +static inline u32 ilog2_w(u64 n) +{ + return ilog2(n * n * n * n); +} + +static u32 shannon_entropy(struct heuristic_ws *ws) +{ + const u32 entropy_max = 8 * ilog2_w(2); + u32 entropy_sum = 0; + u32 p, p_base, sz_base; + u32 i; + + sz_base = ilog2_w(ws->sample_size); + for (i = 0; i < BUCKET_SIZE && ws->bucket[i].count > 0; i++) { + p = ws->bucket[i].count; + p_base = ilog2_w(p); + entropy_sum += p * (sz_base - p_base); + } + + entropy_sum /= ws->sample_size; + return entropy_sum * 100 / entropy_max; +} + +#define RADIX_BASE 4U +#define COUNTERS_SIZE (1U << RADIX_BASE) + +static u8 get4bits(u64 num, int shift) { + u8 low4bits; + + num >>= shift; + /* Reverse order */ + low4bits = (COUNTERS_SIZE - 1) - (num % COUNTERS_SIZE); + return low4bits; +} + +/* + * Use 4 bits as radix base + * Use 16 u32 counters for calculating new position in buf array + * + * @array - array that will be sorted + * @array_buf - buffer array to store sorting results + * must be equal in size to @array + * @num - array size + */ +static void radix_sort(struct bucket_item *array, struct bucket_item *array_buf, + int num) +{ + u64 max_num; + u64 buf_num; + u32 counters[COUNTERS_SIZE]; + u32 new_addr; + u32 addr; + int bitlen; + int shift; + int i; + + /* + * Try avoid useless loop iterations for small numbers stored in big + * counters. Example: 48 33 4 ... in 64bit array + */ + max_num = array[0].count; + for (i = 1; i < num; i++) { + buf_num = array[i].count; + if (buf_num > max_num) + max_num = buf_num; + } + + buf_num = ilog2(max_num); + bitlen = ALIGN(buf_num, RADIX_BASE * 2); + + shift = 0; + while (shift < bitlen) { + memset(counters, 0, sizeof(counters)); + + for (i = 0; i < num; i++) { + buf_num = array[i].count; + addr = get4bits(buf_num, shift); + counters[addr]++; + } + + for (i = 1; i < COUNTERS_SIZE; i++) + counters[i] += counters[i - 1]; + + for (i = num - 1; i >= 0; i--) { + buf_num = array[i].count; + addr = get4bits(buf_num, shift); + counters[addr]--; + new_addr = counters[addr]; + array_buf[new_addr] = array[i]; + } + + shift += RADIX_BASE; + + /* + * Normal radix expects to move data from a temporary array, to + * the main one. But that requires some CPU time. Avoid that + * by doing another sort iteration to original array instead of + * memcpy() + */ + memset(counters, 0, sizeof(counters)); + + for (i = 0; i < num; i ++) { + buf_num = array_buf[i].count; + addr = get4bits(buf_num, shift); + counters[addr]++; + } + + for (i = 1; i < COUNTERS_SIZE; i++) + counters[i] += counters[i - 1]; + + for (i = num - 1; i >= 0; i--) { + buf_num = array_buf[i].count; + addr = get4bits(buf_num, shift); + counters[addr]--; + new_addr = counters[addr]; + array[new_addr] = array_buf[i]; + } + + shift += RADIX_BASE; + } +} + +/* + * Size of the core byte set - how many bytes cover 90% of the sample + * + * There are several types of structured binary data that use nearly all byte + * values. The distribution can be uniform and counts in all buckets will be + * nearly the same (eg. encrypted data). Unlikely to be compressible. + * + * Other possibility is normal (Gaussian) distribution, where the data could + * be potentially compressible, but we have to take a few more steps to decide + * how much. + * + * @BYTE_CORE_SET_LOW - main part of byte values repeated frequently, + * compression algo can easy fix that + * @BYTE_CORE_SET_HIGH - data have uniform distribution and with high + * probability is not compressible + */ +#define BYTE_CORE_SET_LOW (64) +#define BYTE_CORE_SET_HIGH (200) + +static int byte_core_set_size(struct heuristic_ws *ws) +{ + u32 i; + u32 coreset_sum = 0; + const u32 core_set_threshold = ws->sample_size * 90 / 100; + struct bucket_item *bucket = ws->bucket; + + /* Sort in reverse order */ + radix_sort(ws->bucket, ws->bucket_b, BUCKET_SIZE); + + for (i = 0; i < BYTE_CORE_SET_LOW; i++) + coreset_sum += bucket[i].count; + + if (coreset_sum > core_set_threshold) + return i; + + for (; i < BYTE_CORE_SET_HIGH && bucket[i].count > 0; i++) { + coreset_sum += bucket[i].count; + if (coreset_sum > core_set_threshold) + break; + } + + return i; +} + +/* + * Count byte values in buckets. + * This heuristic can detect textual data (configs, xml, json, html, etc). + * Because in most text-like data byte set is restricted to limited number of + * possible characters, and that restriction in most cases makes data easy to + * compress. + * + * @BYTE_SET_THRESHOLD - consider all data within this byte set size: + * less - compressible + * more - need additional analysis + */ +#define BYTE_SET_THRESHOLD (64) + +static u32 byte_set_size(const struct heuristic_ws *ws) +{ + u32 i; + u32 byte_set_size = 0; + + for (i = 0; i < BYTE_SET_THRESHOLD; i++) { + if (ws->bucket[i].count > 0) + byte_set_size++; + } + + /* + * Continue collecting count of byte values in buckets. If the byte + * set size is bigger then the threshold, it's pointless to continue, + * the detection technique would fail for this type of data. + */ + for (; i < BUCKET_SIZE; i++) { + if (ws->bucket[i].count > 0) { + byte_set_size++; + if (byte_set_size > BYTE_SET_THRESHOLD) + return byte_set_size; + } + } + + return byte_set_size; +} + +static bool sample_repeated_patterns(struct heuristic_ws *ws) +{ + const u32 half_of_sample = ws->sample_size / 2; + const u8 *data = ws->sample; + + return memcmp(&data[0], &data[half_of_sample], half_of_sample) == 0; +} + +static void heuristic_collect_sample(struct inode *inode, u64 start, u64 end, + struct heuristic_ws *ws) +{ + struct page *page; + u64 index, index_end; + u32 i, curr_sample_pos; + u8 *in_data; + + /* + * Compression handles the input data by chunks of 128KiB + * (defined by BTRFS_MAX_UNCOMPRESSED) + * + * We do the same for the heuristic and loop over the whole range. + * + * MAX_SAMPLE_SIZE - calculated under assumption that heuristic will + * process no more than BTRFS_MAX_UNCOMPRESSED at a time. + */ + if (end - start > BTRFS_MAX_UNCOMPRESSED) + end = start + BTRFS_MAX_UNCOMPRESSED; + + index = start >> PAGE_SHIFT; + index_end = end >> PAGE_SHIFT; + + /* Don't miss unaligned end */ + if (!IS_ALIGNED(end, PAGE_SIZE)) + index_end++; + + curr_sample_pos = 0; + while (index < index_end) { + page = find_get_page(inode->i_mapping, index); + in_data = kmap(page); + /* Handle case where the start is not aligned to PAGE_SIZE */ + i = start % PAGE_SIZE; + while (i < PAGE_SIZE - SAMPLING_READ_SIZE) { + /* Don't sample any garbage from the last page */ + if (start > end - SAMPLING_READ_SIZE) + break; + memcpy(&ws->sample[curr_sample_pos], &in_data[i], + SAMPLING_READ_SIZE); + i += SAMPLING_INTERVAL; + start += SAMPLING_INTERVAL; + curr_sample_pos += SAMPLING_READ_SIZE; + } + kunmap(page); + put_page(page); + + index++; + } + + ws->sample_size = curr_sample_pos; +} + +/* + * Compression heuristic. + * + * For now is's a naive and optimistic 'return true', we'll extend the logic to + * quickly (compared to direct compression) detect data characteristics + * (compressible/uncompressible) to avoid wasting CPU time on uncompressible + * data. + * + * The following types of analysis can be performed: + * - detect mostly zero data + * - detect data with low "byte set" size (text, etc) + * - detect data with low/high "core byte" set + * + * Return non-zero if the compression should be done, 0 otherwise. + */ +int btrfs_compress_heuristic(struct inode *inode, u64 start, u64 end) +{ + struct list_head *ws_list = get_workspace(0, 0); + struct heuristic_ws *ws; + u32 i; + u8 byte; + int ret = 0; + + ws = list_entry(ws_list, struct heuristic_ws, list); + + heuristic_collect_sample(inode, start, end, ws); + + if (sample_repeated_patterns(ws)) { + ret = 1; + goto out; + } + + memset(ws->bucket, 0, sizeof(*ws->bucket)*BUCKET_SIZE); + + for (i = 0; i < ws->sample_size; i++) { + byte = ws->sample[i]; + ws->bucket[byte].count++; + } + + i = byte_set_size(ws); + if (i < BYTE_SET_THRESHOLD) { + ret = 2; + goto out; + } + + i = byte_core_set_size(ws); + if (i <= BYTE_CORE_SET_LOW) { + ret = 3; + goto out; + } + + if (i >= BYTE_CORE_SET_HIGH) { + ret = 0; + goto out; + } + + i = shannon_entropy(ws); + if (i <= ENTROPY_LVL_ACEPTABLE) { + ret = 4; + goto out; + } + + /* + * For the levels below ENTROPY_LVL_HIGH, additional analysis would be + * needed to give green light to compression. + * + * For now just assume that compression at that level is not worth the + * resources because: + * + * 1. it is possible to defrag the data later + * + * 2. the data would turn out to be hardly compressible, eg. 150 byte + * values, every bucket has counter at level ~54. The heuristic would + * be confused. This can happen when data have some internal repeated + * patterns like "abbacbbc...". This can be detected by analyzing + * pairs of bytes, which is too costly. + */ + if (i < ENTROPY_LVL_HIGH) { + ret = 5; + goto out; + } else { + ret = 0; + goto out; + } + +out: + put_workspace(0, ws_list); + return ret; +} + +/* + * Convert the compression suffix (eg. after "zlib" starting with ":") to + * level, unrecognized string will set the default level + */ +unsigned int btrfs_compress_str2level(unsigned int type, const char *str) +{ + unsigned int level = 0; + int ret; + + if (!type) + return 0; + + if (str[0] == ':') { + ret = kstrtouint(str + 1, 10, &level); + if (ret) + level = 0; + } + + level = btrfs_compress_set_level(type, level); + + return level; +} |