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Diffstat (limited to '')
| -rw-r--r-- | fs/btrfs/compression.c | 1747 |
1 files changed, 1747 insertions, 0 deletions
diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c new file mode 100644 index 000000000..e6635fe70 --- /dev/null +++ b/fs/btrfs/compression.c @@ -0,0 +1,1747 @@ +// 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/pagevec.h> +#include <linux/highmem.h> +#include <linux/kthread.h> +#include <linux/time.h> +#include <linux/init.h> +#include <linux/string.h> +#include <linux/backing-dev.h> +#include <linux/writeback.h> +#include <linux/psi.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" +#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 void finish_compressed_bio_read(struct compressed_bio *cb) +{ + unsigned int index; + struct page *page; + + if (cb->status == BLK_STS_OK) + cb->status = errno_to_blk_status(btrfs_decompress_bio(cb)); + + /* 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 */ + btrfs_bio_end_io(btrfs_bio(cb->orig_bio), cb->status); + + /* Finally free the cb struct */ + kfree(cb->compressed_pages); + kfree(cb); +} + +/* + * Verify the checksums and kick off repair if needed on the uncompressed data + * before decompressing it into the original bio and freeing the uncompressed + * pages. + */ +static void end_compressed_bio_read(struct btrfs_bio *bbio) +{ + struct compressed_bio *cb = bbio->private; + struct inode *inode = cb->inode; + struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb); + struct btrfs_inode *bi = BTRFS_I(inode); + bool csum = !(bi->flags & BTRFS_INODE_NODATASUM) && + !test_bit(BTRFS_FS_STATE_NO_CSUMS, &fs_info->fs_state); + blk_status_t status = bbio->bio.bi_status; + struct bvec_iter iter; + struct bio_vec bv; + u32 offset; + + btrfs_bio_for_each_sector(fs_info, bv, bbio, iter, offset) { + u64 start = bbio->file_offset + offset; + + if (!status && + (!csum || !btrfs_check_data_csum(inode, bbio, offset, + bv.bv_page, bv.bv_offset))) { + btrfs_clean_io_failure(bi, start, bv.bv_page, + bv.bv_offset); + } else { + int ret; + + refcount_inc(&cb->pending_ios); + ret = btrfs_repair_one_sector(inode, bbio, offset, + bv.bv_page, bv.bv_offset, + btrfs_submit_data_read_bio); + if (ret) { + refcount_dec(&cb->pending_ios); + status = errno_to_blk_status(ret); + } + } + } + + if (status) + cb->status = status; + + if (refcount_dec_and_test(&cb->pending_ios)) + finish_compressed_bio_read(cb); + btrfs_bio_free_csum(bbio); + bio_put(&bbio->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 folio_batch fbatch; + const int errno = blk_status_to_errno(cb->status); + int i; + int ret; + + if (errno) + mapping_set_error(inode->i_mapping, errno); + + folio_batch_init(&fbatch); + while (index <= end_index) { + ret = filemap_get_folios(inode->i_mapping, &index, end_index, + &fbatch); + + if (ret == 0) + return; + + for (i = 0; i < ret; i++) { + struct folio *folio = fbatch.folios[i]; + + if (errno) + folio_set_error(folio); + btrfs_page_clamp_clear_writeback(fs_info, &folio->page, + cb->start, cb->len); + } + folio_batch_release(&fbatch); + } + /* 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); +} + +static void btrfs_finish_compressed_write_work(struct work_struct *work) +{ + struct compressed_bio *cb = + container_of(work, struct compressed_bio, write_end_work); + + finish_compressed_bio_write(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 btrfs_bio *bbio) +{ + struct compressed_bio *cb = bbio->private; + + if (bbio->bio.bi_status) + cb->status = bbio->bio.bi_status; + + if (refcount_dec_and_test(&cb->pending_ios)) { + struct btrfs_fs_info *fs_info = btrfs_sb(cb->inode->i_sb); + + btrfs_record_physical_zoned(cb->inode, cb->start, &bbio->bio); + queue_work(fs_info->compressed_write_workers, &cb->write_end_work); + } + bio_put(&bbio->bio); +} + +/* + * 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, + btrfs_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, opf, endio_func, cb); + bio->bi_iter.bi_sector = disk_bytenr >> SECTOR_SHIFT; + + 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; + refcount_inc(&cb->pending_ios); + 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 = BLK_STS_OK; + 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(sizeof(struct compressed_bio), GFP_NOFS); + if (!cb) + return BLK_STS_RESOURCE; + refcount_set(&cb->pending_ios, 1); + cb->status = BLK_STS_OK; + cb->inode = &inode->vfs_inode; + cb->start = start; + cb->len = len; + cb->compressed_pages = compressed_pages; + cb->compressed_len = compressed_len; + cb->writeback = writeback; + INIT_WORK(&cb->write_end_work, btrfs_finish_compressed_write_work); + 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)); + break; + } + 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) { + btrfs_bio_end_io(btrfs_bio(bio), ret); + break; + } + } + + ASSERT(bio->bi_iter.bi_size); + btrfs_submit_bio(fs_info, bio, 0); + bio = NULL; + } + cond_resched(); + } + + if (blkcg_css) + kthread_associate_blkcg(NULL); + + if (refcount_dec_and_test(&cb->pending_ios)) + 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, + int *memstall, unsigned long *pflags) +{ + 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; + } + + if (!*memstall && PageWorkingset(page)) { + psi_memstall_enter(pflags); + *memstall = 1; + } + + 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, NULL); + 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, NULL); + 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); + } + } + + 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, NULL); + 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; + unsigned long pflags; + int memstall = 0; + blk_status_t ret; + int ret2; + int i; + + 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(sizeof(struct compressed_bio), GFP_NOFS); + if (!cb) { + ret = BLK_STS_RESOURCE; + goto out; + } + + refcount_set(&cb->pending_ios, 1); + cb->status = BLK_STS_OK; + cb->inode = inode; + + 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, &memstall, &pflags); + + /* 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)) { + cb->status = errno_to_blk_status(PTR_ERR(comp_bio)); + break; + } + } + /* + * 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) { + /* Save the original iter for read repair */ + if (bio_op(comp_bio) == REQ_OP_READ) + btrfs_bio(comp_bio)->iter = comp_bio->bi_iter; + + /* + * Save the initial offset of this chunk, as there + * is no direct correlation between compressed pages and + * the original file offset. The field is only used for + * priting error messages. + */ + btrfs_bio(comp_bio)->file_offset = file_offset; + + ret = btrfs_lookup_bio_sums(inode, comp_bio, NULL); + if (ret) { + btrfs_bio_end_io(btrfs_bio(comp_bio), ret); + break; + } + + ASSERT(comp_bio->bi_iter.bi_size); + btrfs_submit_bio(fs_info, comp_bio, mirror_num); + comp_bio = NULL; + } + } + + if (memstall) + psi_memstall_leave(&pflags); + + if (refcount_dec_and_test(&cb->pending_ios)) + finish_compressed_bio_read(cb); + 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); + btrfs_bio_end_io(btrfs_bio(bio), ret); + return; +} + +/* + * 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); + 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; +} |