// SPDX-License-Identifier: GPL-2.0 /* * Copyright (C) 2008 Oracle. All rights reserved. */ #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #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" #include "subpage.h" #include "zoned.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(struct list_head *ws, struct compressed_bio *cb) { switch (cb->compress_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) { return sizeof(struct compressed_bio) + (DIV_ROUND_UP(disk_size, fs_info->sectorsize)) * fs_info->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 u32 csum_size = fs_info->csum_size; const u32 sectorsize = fs_info->sectorsize; struct page *page; unsigned int 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) || test_bit(BTRFS_FS_STATE_NO_CSUMS, &fs_info->fs_state)) return 0; shash->tfm = fs_info->csum_shash; for (i = 0; i < cb->nr_pages; i++) { u32 pg_offset; u32 bytes_left = PAGE_SIZE; page = cb->compressed_pages[i]; /* Determine the remaining bytes inside the page first */ if (i == cb->nr_pages - 1) bytes_left = cb->compressed_len - i * PAGE_SIZE; /* Hash through the page sector by sector */ for (pg_offset = 0; pg_offset < bytes_left; pg_offset += sectorsize) { kaddr = kmap_atomic(page); crypto_shash_digest(shash, kaddr + pg_offset, sectorsize, csum); kunmap_atomic(kaddr); if (memcmp(&csum, cb_sum, csum_size) != 0) { btrfs_print_data_csum_error(inode, disk_start, csum, cb_sum, cb->mirror_num); if (btrfs_bio(bio)->device) btrfs_dev_stat_inc_and_print( btrfs_bio(bio)->device, BTRFS_DEV_STAT_CORRUPTION_ERRS); return -EIO; } cb_sum += csum_size; disk_start += sectorsize; } } return 0; } /* * Reduce bio and io accounting for a compressed_bio with its corresponding bio. * * Return true if there is no pending bio nor io. * Return false otherwise. */ static bool dec_and_test_compressed_bio(struct compressed_bio *cb, struct bio *bio) { struct btrfs_fs_info *fs_info = btrfs_sb(cb->inode->i_sb); unsigned int bi_size = 0; bool last_io = false; struct bio_vec *bvec; struct bvec_iter_all iter_all; /* * At endio time, bi_iter.bi_size doesn't represent the real bio size. * Thus here we have to iterate through all segments to grab correct * bio size. */ bio_for_each_segment_all(bvec, bio, iter_all) bi_size += bvec->bv_len; if (bio->bi_status) cb->status = bio->bi_status; ASSERT(bi_size && bi_size <= cb->compressed_len); last_io = refcount_sub_and_test(bi_size >> fs_info->sectorsize_bits, &cb->pending_sectors); /* * Here we must wake up the possible error handler after all other * operations on @cb finished, or we can race with * finish_compressed_bio_*() which may free @cb. */ wake_up_var(cb); return last_io; } static void finish_compressed_bio_read(struct compressed_bio *cb) { unsigned int index; struct page *page; /* Release the compressed pages */ 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->status != BLK_STS_OK) { cb->orig_bio->bi_status = cb->status; bio_endio(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(cb->orig_bio, BIO_CLONED)); bio_for_each_segment_all(bvec, cb->orig_bio, iter_all) { u64 bvec_start = page_offset(bvec->bv_page) + bvec->bv_offset; btrfs_page_set_checked(btrfs_sb(cb->inode->i_sb), bvec->bv_page, bvec_start, bvec->bv_len); } bio_endio(cb->orig_bio); } /* Finally free the cb struct */ kfree(cb->compressed_pages); kfree(cb); } /* 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; unsigned int mirror = btrfs_bio(bio)->mirror_num; int ret = 0; if (!dec_and_test_compressed_bio(cb, bio)) goto out; /* * Record the correct mirror_num in cb->orig_bio so that * read-repair can work properly. */ btrfs_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->status != BLK_STS_OK) goto csum_failed; inode = cb->inode; ret = check_compressed_csum(BTRFS_I(inode), bio, 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->status = errno_to_blk_status(ret); finish_compressed_bio_read(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) { struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb); 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; const int errno = blk_status_to_errno(cb->status); int i; int ret; if (errno) mapping_set_error(inode->i_mapping, errno); 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 (errno) SetPageError(pages[i]); btrfs_page_clamp_clear_writeback(fs_info, pages[i], cb->start, cb->len); put_page(pages[i]); } nr_pages -= ret; index += ret; } /* the inode may be gone now */ } static void finish_compressed_bio_write(struct compressed_bio *cb) { struct inode *inode = cb->inode; unsigned int index; /* * 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. */ btrfs_writepage_endio_finish_ordered(BTRFS_I(inode), NULL, cb->start, cb->start + cb->len - 1, cb->status == BLK_STS_OK); if (cb->writeback) 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 */ for (index = 0; index < cb->nr_pages; index++) { struct page *page = cb->compressed_pages[index]; page->mapping = NULL; put_page(page); } /* Finally free the cb struct */ kfree(cb->compressed_pages); kfree(cb); } /* * 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; if (!dec_and_test_compressed_bio(cb, bio)) goto out; btrfs_record_physical_zoned(cb->inode, cb->start, bio); finish_compressed_bio_write(cb); out: bio_put(bio); } static blk_status_t submit_compressed_bio(struct btrfs_fs_info *fs_info, struct bio *bio, int mirror_num) { blk_status_t ret; ASSERT(bio->bi_iter.bi_size); ret = btrfs_bio_wq_end_io(fs_info, bio, BTRFS_WQ_ENDIO_DATA); if (ret) return ret; ret = btrfs_map_bio(fs_info, bio, mirror_num); return ret; } /* * Allocate a compressed_bio, which will be used to read/write on-disk * (aka, compressed) * data. * * @cb: The compressed_bio structure, which records all the needed * information to bind the compressed data to the uncompressed * page cache. * @disk_byten: The logical bytenr where the compressed data will be read * from or written to. * @endio_func: The endio function to call after the IO for compressed data * is finished. * @next_stripe_start: Return value of logical bytenr of where next stripe starts. * Let the caller know to only fill the bio up to the stripe * boundary. */ static struct bio *alloc_compressed_bio(struct compressed_bio *cb, u64 disk_bytenr, blk_opf_t opf, bio_end_io_t endio_func, u64 *next_stripe_start) { struct btrfs_fs_info *fs_info = btrfs_sb(cb->inode->i_sb); struct btrfs_io_geometry geom; struct extent_map *em; struct bio *bio; int ret; bio = btrfs_bio_alloc(BIO_MAX_VECS); bio->bi_iter.bi_sector = disk_bytenr >> SECTOR_SHIFT; bio->bi_opf = opf; bio->bi_private = cb; bio->bi_end_io = endio_func; em = btrfs_get_chunk_map(fs_info, disk_bytenr, fs_info->sectorsize); if (IS_ERR(em)) { bio_put(bio); return ERR_CAST(em); } if (bio_op(bio) == REQ_OP_ZONE_APPEND) bio_set_dev(bio, em->map_lookup->stripes[0].dev->bdev); ret = btrfs_get_io_geometry(fs_info, em, btrfs_op(bio), disk_bytenr, &geom); free_extent_map(em); if (ret < 0) { bio_put(bio); return ERR_PTR(ret); } *next_stripe_start = disk_bytenr + geom.len; return 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 int len, u64 disk_start, unsigned int compressed_len, struct page **compressed_pages, unsigned int nr_pages, blk_opf_t write_flags, struct cgroup_subsys_state *blkcg_css, bool writeback) { struct btrfs_fs_info *fs_info = inode->root->fs_info; struct bio *bio = NULL; struct compressed_bio *cb; u64 cur_disk_bytenr = disk_start; u64 next_stripe_start; blk_status_t ret; int skip_sum = inode->flags & BTRFS_INODE_NODATASUM; const bool use_append = btrfs_use_zone_append(inode, disk_start); const enum req_op bio_op = use_append ? REQ_OP_ZONE_APPEND : REQ_OP_WRITE; ASSERT(IS_ALIGNED(start, fs_info->sectorsize) && IS_ALIGNED(len, fs_info->sectorsize)); cb = kmalloc(compressed_bio_size(fs_info, compressed_len), GFP_NOFS); if (!cb) return BLK_STS_RESOURCE; refcount_set(&cb->pending_sectors, compressed_len >> fs_info->sectorsize_bits); cb->status = BLK_STS_OK; 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->writeback = writeback; cb->orig_bio = NULL; cb->nr_pages = nr_pages; if (blkcg_css) kthread_associate_blkcg(blkcg_css); while (cur_disk_bytenr < disk_start + compressed_len) { u64 offset = cur_disk_bytenr - disk_start; unsigned int index = offset >> PAGE_SHIFT; unsigned int real_size; unsigned int added; struct page *page = compressed_pages[index]; bool submit = false; /* Allocate new bio if submitted or not yet allocated */ if (!bio) { bio = alloc_compressed_bio(cb, cur_disk_bytenr, bio_op | write_flags, end_compressed_bio_write, &next_stripe_start); if (IS_ERR(bio)) { ret = errno_to_blk_status(PTR_ERR(bio)); bio = NULL; goto finish_cb; } if (blkcg_css) bio->bi_opf |= REQ_CGROUP_PUNT; } /* * We should never reach next_stripe_start start as we will * submit comp_bio when reach the boundary immediately. */ ASSERT(cur_disk_bytenr != next_stripe_start); /* * We have various limits on the real read size: * - stripe boundary * - page boundary * - compressed length boundary */ real_size = min_t(u64, U32_MAX, next_stripe_start - cur_disk_bytenr); real_size = min_t(u64, real_size, PAGE_SIZE - offset_in_page(offset)); real_size = min_t(u64, real_size, compressed_len - offset); ASSERT(IS_ALIGNED(real_size, fs_info->sectorsize)); if (use_append) added = bio_add_zone_append_page(bio, page, real_size, offset_in_page(offset)); else added = bio_add_page(bio, page, real_size, offset_in_page(offset)); /* Reached zoned boundary */ if (added == 0) submit = true; cur_disk_bytenr += added; /* Reached stripe boundary */ if (cur_disk_bytenr == next_stripe_start) submit = true; /* Finished the range */ if (cur_disk_bytenr == disk_start + compressed_len) submit = true; if (submit) { if (!skip_sum) { ret = btrfs_csum_one_bio(inode, bio, start, true); if (ret) goto finish_cb; } ret = submit_compressed_bio(fs_info, bio, 0); if (ret) goto finish_cb; bio = NULL; } cond_resched(); } if (blkcg_css) kthread_associate_blkcg(NULL); return 0; finish_cb: if (blkcg_css) kthread_associate_blkcg(NULL); if (bio) { bio->bi_status = ret; bio_endio(bio); } /* Last byte of @cb is submitted, endio will free @cb */ if (cur_disk_bytenr == disk_start + compressed_len) return ret; wait_var_event(cb, refcount_read(&cb->pending_sectors) == (disk_start + compressed_len - cur_disk_bytenr) >> fs_info->sectorsize_bits); /* * Even with previous bio ended, we should still have io not yet * submitted, thus need to finish manually. */ ASSERT(refcount_read(&cb->pending_sectors)); /* Now we are the only one referring @cb, can finish it safely. */ finish_compressed_bio_write(cb); return ret; } 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; } /* * Add extra pages in the same compressed file extent so that we don't need to * re-read the same extent again and again. * * NOTE: this won't work well for subpage, as for subpage read, we lock the * full page then submit bio for each compressed/regular extents. * * This means, if we have several sectors in the same page points to the same * on-disk compressed data, we will re-read the same extent many times and * this function can only help for the next page. */ static noinline int add_ra_bio_pages(struct inode *inode, u64 compressed_end, struct compressed_bio *cb) { struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb); unsigned long end_index; u64 cur = bio_end_offset(cb->orig_bio); u64 isize = i_size_read(inode); int ret; struct page *page; struct extent_map *em; struct address_space *mapping = inode->i_mapping; struct extent_map_tree *em_tree; struct extent_io_tree *tree; int sectors_missed = 0; em_tree = &BTRFS_I(inode)->extent_tree; tree = &BTRFS_I(inode)->io_tree; if (isize == 0) return 0; /* * For current subpage support, we only support 64K page size, * which means maximum compressed extent size (128K) is just 2x page * size. * This makes readahead less effective, so here disable readahead for * subpage for now, until full compressed write is supported. */ if (btrfs_sb(inode->i_sb)->sectorsize < PAGE_SIZE) return 0; end_index = (i_size_read(inode) - 1) >> PAGE_SHIFT; while (cur < compressed_end) { u64 page_end; u64 pg_index = cur >> PAGE_SHIFT; u32 add_size; if (pg_index > end_index) break; page = xa_load(&mapping->i_pages, pg_index); if (page && !xa_is_value(page)) { sectors_missed += (PAGE_SIZE - offset_in_page(cur)) >> fs_info->sectorsize_bits; /* Beyond threshold, no need to continue */ if (sectors_missed > 4) break; /* * Jump to next page start as we already have page for * current offset. */ cur = (pg_index << PAGE_SHIFT) + PAGE_SIZE; continue; } 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); /* There is already a page, skip to page end */ cur = (pg_index << PAGE_SHIFT) + PAGE_SIZE; continue; } ret = set_page_extent_mapped(page); if (ret < 0) { unlock_page(page); put_page(page); break; } page_end = (pg_index << PAGE_SHIFT) + PAGE_SIZE - 1; lock_extent(tree, cur, page_end); read_lock(&em_tree->lock); em = lookup_extent_mapping(em_tree, cur, page_end + 1 - cur); read_unlock(&em_tree->lock); /* * 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. */ if (!em || cur < em->start || (cur + fs_info->sectorsize > extent_map_end(em)) || (em->block_start >> 9) != cb->orig_bio->bi_iter.bi_sector) { free_extent_map(em); unlock_extent(tree, cur, page_end); unlock_page(page); put_page(page); break; } free_extent_map(em); if (page->index == end_index) { size_t zero_offset = offset_in_page(isize); if (zero_offset) { int zeros; zeros = PAGE_SIZE - zero_offset; memzero_page(page, zero_offset, zeros); flush_dcache_page(page); } } add_size = min(em->start + em->len, page_end + 1) - cur; ret = bio_add_page(cb->orig_bio, page, add_size, offset_in_page(cur)); if (ret != add_size) { unlock_extent(tree, cur, page_end); unlock_page(page); put_page(page); break; } /* * If it's subpage, we also need to increase its * subpage::readers number, as at endio we will decrease * subpage::readers and to unlock the page. */ if (fs_info->sectorsize < PAGE_SIZE) btrfs_subpage_start_reader(fs_info, page, cur, add_size); put_page(page); cur += add_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 */ void btrfs_submit_compressed_read(struct inode *inode, struct bio *bio, int mirror_num) { struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb); struct extent_map_tree *em_tree; struct compressed_bio *cb; unsigned int compressed_len; struct bio *comp_bio = NULL; const u64 disk_bytenr = bio->bi_iter.bi_sector << SECTOR_SHIFT; u64 cur_disk_byte = disk_bytenr; u64 next_stripe_start; u64 file_offset; u64 em_len; u64 em_start; struct extent_map *em; blk_status_t ret; int ret2; int i; u8 *sums; em_tree = &BTRFS_I(inode)->extent_tree; file_offset = bio_first_bvec_all(bio)->bv_offset + page_offset(bio_first_page_all(bio)); /* we need the actual starting offset of this extent in the file */ read_lock(&em_tree->lock); em = lookup_extent_mapping(em_tree, file_offset, fs_info->sectorsize); read_unlock(&em_tree->lock); if (!em) { ret = BLK_STS_IOERR; goto out; } ASSERT(em->compress_type != BTRFS_COMPRESS_NONE); compressed_len = em->block_len; cb = kmalloc(compressed_bio_size(fs_info, compressed_len), GFP_NOFS); if (!cb) { ret = BLK_STS_RESOURCE; goto out; } refcount_set(&cb->pending_sectors, compressed_len >> fs_info->sectorsize_bits); cb->status = BLK_STS_OK; cb->inode = inode; cb->mirror_num = mirror_num; sums = cb->sums; cb->start = em->orig_start; em_len = em->len; em_start = em->start; cb->len = bio->bi_iter.bi_size; cb->compressed_len = compressed_len; cb->compress_type = em->compress_type; cb->orig_bio = bio; free_extent_map(em); em = NULL; cb->nr_pages = DIV_ROUND_UP(compressed_len, PAGE_SIZE); cb->compressed_pages = kcalloc(cb->nr_pages, sizeof(struct page *), GFP_NOFS); if (!cb->compressed_pages) { ret = BLK_STS_RESOURCE; goto fail; } ret2 = btrfs_alloc_page_array(cb->nr_pages, cb->compressed_pages); if (ret2) { ret = BLK_STS_RESOURCE; goto fail; } 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; while (cur_disk_byte < disk_bytenr + compressed_len) { u64 offset = cur_disk_byte - disk_bytenr; unsigned int index = offset >> PAGE_SHIFT; unsigned int real_size; unsigned int added; struct page *page = cb->compressed_pages[index]; bool submit = false; /* Allocate new bio if submitted or not yet allocated */ if (!comp_bio) { comp_bio = alloc_compressed_bio(cb, cur_disk_byte, REQ_OP_READ, end_compressed_bio_read, &next_stripe_start); if (IS_ERR(comp_bio)) { ret = errno_to_blk_status(PTR_ERR(comp_bio)); comp_bio = NULL; goto finish_cb; } } /* * We should never reach next_stripe_start start as we will * submit comp_bio when reach the boundary immediately. */ ASSERT(cur_disk_byte != next_stripe_start); /* * We have various limit on the real read size: * - stripe boundary * - page boundary * - compressed length boundary */ real_size = min_t(u64, U32_MAX, next_stripe_start - cur_disk_byte); real_size = min_t(u64, real_size, PAGE_SIZE - offset_in_page(offset)); real_size = min_t(u64, real_size, compressed_len - offset); ASSERT(IS_ALIGNED(real_size, fs_info->sectorsize)); added = bio_add_page(comp_bio, page, real_size, offset_in_page(offset)); /* * Maximum compressed extent is smaller than bio size limit, * thus bio_add_page() should always success. */ ASSERT(added == real_size); cur_disk_byte += added; /* Reached stripe boundary, need to submit */ if (cur_disk_byte == next_stripe_start) submit = true; /* Has finished the range, need to submit */ if (cur_disk_byte == disk_bytenr + compressed_len) submit = true; if (submit) { unsigned int nr_sectors; ret = btrfs_lookup_bio_sums(inode, comp_bio, sums); if (ret) goto finish_cb; nr_sectors = DIV_ROUND_UP(comp_bio->bi_iter.bi_size, fs_info->sectorsize); sums += fs_info->csum_size * nr_sectors; ret = submit_compressed_bio(fs_info, comp_bio, mirror_num); if (ret) goto finish_cb; comp_bio = NULL; } } return; fail: if (cb->compressed_pages) { for (i = 0; i < cb->nr_pages; i++) { if (cb->compressed_pages[i]) __free_page(cb->compressed_pages[i]); } } kfree(cb->compressed_pages); kfree(cb); out: free_extent_map(em); bio->bi_status = ret; bio_endio(bio); return; finish_cb: if (comp_bio) { comp_bio->bi_status = ret; bio_endio(comp_bio); } /* All bytes of @cb is submitted, endio will free @cb */ if (cur_disk_byte == disk_bytenr + compressed_len) return; wait_var_event(cb, refcount_read(&cb->pending_sectors) == (disk_bytenr + compressed_len - cur_disk_byte) >> fs_info->sectorsize_bits); /* * Even with previous bio ended, we should still have io not yet * submitted, thus need to finish @cb manually. */ ASSERT(refcount_read(&cb->pending_sectors)); /* Now we are the only one referring @cb, can finish it safely. */ finish_compressed_bio_read(cb); } /* * 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 */ 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; } 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(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 decompressed data from working buffer to pages. * * @buf: The decompressed data buffer * @buf_len: The decompressed data length * @decompressed: Number of bytes that are already decompressed inside the * compressed extent * @cb: The compressed extent descriptor * @orig_bio: The original bio that the caller wants to read for * * An easier to understand graph is like below: * * |<- orig_bio ->| |<- orig_bio->| * |<------- full decompressed extent ----->| * |<----------- @cb range ---->| * | |<-- @buf_len -->| * |<--- @decompressed --->| * * Note that, @cb can be a subpage of the full decompressed extent, but * @cb->start always has the same as the orig_file_offset value of the full * decompressed extent. * * When reading compressed extent, we have to read the full compressed extent, * while @orig_bio may only want part of the range. * Thus this function will ensure only data covered by @orig_bio will be copied * to. * * Return 0 if we have copied all needed contents for @orig_bio. * Return >0 if we need continue decompress. */ int btrfs_decompress_buf2page(const char *buf, u32 buf_len, struct compressed_bio *cb, u32 decompressed) { struct bio *orig_bio = cb->orig_bio; /* Offset inside the full decompressed extent */ u32 cur_offset; cur_offset = decompressed; /* The main loop to do the copy */ while (cur_offset < decompressed + buf_len) { struct bio_vec bvec; size_t copy_len; u32 copy_start; /* Offset inside the full decompressed extent */ u32 bvec_offset; bvec = bio_iter_iovec(orig_bio, orig_bio->bi_iter); /* * cb->start may underflow, but subtracting that value can still * give us correct offset inside the full decompressed extent. */ bvec_offset = page_offset(bvec.bv_page) + bvec.bv_offset - cb->start; /* Haven't reached the bvec range, exit */ if (decompressed + buf_len <= bvec_offset) return 1; copy_start = max(cur_offset, bvec_offset); copy_len = min(bvec_offset + bvec.bv_len, decompressed + buf_len) - copy_start; ASSERT(copy_len); /* * Extra range check to ensure we didn't go beyond * @buf + @buf_len. */ ASSERT(copy_start - decompressed < buf_len); memcpy_to_page(bvec.bv_page, bvec.bv_offset, buf + copy_start - decompressed, copy_len); flush_dcache_page(bvec.bv_page); cur_offset += copy_len; bio_advance(orig_bio, copy_len); /* Finished the bio */ if (!orig_bio->bi_iter.bi_size) return 0; } 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_local_page(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_local(in_data); 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; }