| /* |
| * Copyright (C) 2008 Oracle. All rights reserved. |
| * |
| * This program is free software; you can redistribute it and/or |
| * modify it under the terms of the GNU General Public |
| * License v2 as published by the Free Software Foundation. |
| * |
| * This program is distributed in the hope that it will be useful, |
| * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
| * General Public License for more details. |
| * |
| * You should have received a copy of the GNU General Public |
| * License along with this program; if not, write to the |
| * Free Software Foundation, Inc., 59 Temple Place - Suite 330, |
| * Boston, MA 021110-1307, USA. |
| */ |
| |
| #include <linux/kernel.h> |
| #include <linux/bio.h> |
| #include <linux/buffer_head.h> |
| #include <linux/file.h> |
| #include <linux/fs.h> |
| #include <linux/pagemap.h> |
| #include <linux/highmem.h> |
| #include <linux/time.h> |
| #include <linux/init.h> |
| #include <linux/string.h> |
| #include <linux/backing-dev.h> |
| #include <linux/mpage.h> |
| #include <linux/swap.h> |
| #include <linux/writeback.h> |
| #include <linux/bit_spinlock.h> |
| #include <linux/slab.h> |
| #include <linux/sched/mm.h> |
| #include <linux/sort.h> |
| #include <linux/log2.h> |
| #include "ctree.h" |
| #include "disk-io.h" |
| #include "transaction.h" |
| #include "btrfs_inode.h" |
| #include "volumes.h" |
| #include "ordered-data.h" |
| #include "compression.h" |
| #include "extent_io.h" |
| #include "extent_map.h" |
| |
| static int btrfs_decompress_bio(struct compressed_bio *cb); |
| |
| static inline int compressed_bio_size(struct btrfs_fs_info *fs_info, |
| unsigned long disk_size) |
| { |
| u16 csum_size = btrfs_super_csum_size(fs_info->super_copy); |
| |
| return sizeof(struct compressed_bio) + |
| (DIV_ROUND_UP(disk_size, fs_info->sectorsize)) * csum_size; |
| } |
| |
| static int check_compressed_csum(struct btrfs_inode *inode, |
| struct compressed_bio *cb, |
| u64 disk_start) |
| { |
| int ret; |
| struct page *page; |
| unsigned long i; |
| char *kaddr; |
| u32 csum; |
| u32 *cb_sum = &cb->sums; |
| |
| if (inode->flags & BTRFS_INODE_NODATASUM) |
| return 0; |
| |
| for (i = 0; i < cb->nr_pages; i++) { |
| page = cb->compressed_pages[i]; |
| csum = ~(u32)0; |
| |
| kaddr = kmap_atomic(page); |
| csum = btrfs_csum_data(kaddr, csum, PAGE_SIZE); |
| btrfs_csum_final(csum, (u8 *)&csum); |
| kunmap_atomic(kaddr); |
| |
| if (csum != *cb_sum) { |
| btrfs_print_data_csum_error(inode, disk_start, csum, |
| *cb_sum, cb->mirror_num); |
| ret = -EIO; |
| goto fail; |
| } |
| cb_sum++; |
| |
| } |
| ret = 0; |
| fail: |
| return ret; |
| } |
| |
| /* when we finish reading compressed pages from the disk, we |
| * decompress them and then run the bio end_io routines on the |
| * decompressed pages (in the inode address space). |
| * |
| * This allows the checksumming and other IO error handling routines |
| * to work normally |
| * |
| * The compressed pages are freed here, and it must be run |
| * in process context |
| */ |
| static void end_compressed_bio_read(struct bio *bio) |
| { |
| struct compressed_bio *cb = bio->bi_private; |
| struct inode *inode; |
| struct page *page; |
| unsigned long index; |
| unsigned int mirror = btrfs_io_bio(bio)->mirror_num; |
| int ret = 0; |
| |
| if (bio->bi_status) |
| cb->errors = 1; |
| |
| /* if there are more bios still pending for this compressed |
| * extent, just exit |
| */ |
| if (!refcount_dec_and_test(&cb->pending_bios)) |
| goto out; |
| |
| /* |
| * Record the correct mirror_num in cb->orig_bio so that |
| * read-repair can work properly. |
| */ |
| ASSERT(btrfs_io_bio(cb->orig_bio)); |
| btrfs_io_bio(cb->orig_bio)->mirror_num = mirror; |
| cb->mirror_num = mirror; |
| |
| /* |
| * Some IO in this cb have failed, just skip checksum as there |
| * is no way it could be correct. |
| */ |
| if (cb->errors == 1) |
| goto csum_failed; |
| |
| inode = cb->inode; |
| ret = check_compressed_csum(BTRFS_I(inode), cb, |
| (u64)bio->bi_iter.bi_sector << 9); |
| if (ret) |
| goto csum_failed; |
| |
| /* ok, we're the last bio for this extent, lets start |
| * the decompression. |
| */ |
| ret = btrfs_decompress_bio(cb); |
| |
| csum_failed: |
| if (ret) |
| cb->errors = 1; |
| |
| /* release the compressed pages */ |
| index = 0; |
| for (index = 0; index < cb->nr_pages; index++) { |
| page = cb->compressed_pages[index]; |
| page->mapping = NULL; |
| put_page(page); |
| } |
| |
| /* do io completion on the original bio */ |
| if (cb->errors) { |
| bio_io_error(cb->orig_bio); |
| } else { |
| int i; |
| struct bio_vec *bvec; |
| |
| /* |
| * we have verified the checksum already, set page |
| * checked so the end_io handlers know about it |
| */ |
| ASSERT(!bio_flagged(bio, BIO_CLONED)); |
| bio_for_each_segment_all(bvec, cb->orig_bio, i) |
| SetPageChecked(bvec->bv_page); |
| |
| bio_endio(cb->orig_bio); |
| } |
| |
| /* finally free the cb struct */ |
| kfree(cb->compressed_pages); |
| kfree(cb); |
| out: |
| bio_put(bio); |
| } |
| |
| /* |
| * Clear the writeback bits on all of the file |
| * pages for a compressed write |
| */ |
| static noinline void end_compressed_writeback(struct inode *inode, |
| const struct compressed_bio *cb) |
| { |
| unsigned long index = cb->start >> PAGE_SHIFT; |
| unsigned long end_index = (cb->start + cb->len - 1) >> PAGE_SHIFT; |
| struct page *pages[16]; |
| unsigned long nr_pages = end_index - index + 1; |
| int i; |
| int ret; |
| |
| if (cb->errors) |
| mapping_set_error(inode->i_mapping, -EIO); |
| |
| while (nr_pages > 0) { |
| ret = find_get_pages_contig(inode->i_mapping, index, |
| min_t(unsigned long, |
| nr_pages, ARRAY_SIZE(pages)), pages); |
| if (ret == 0) { |
| nr_pages -= 1; |
| index += 1; |
| continue; |
| } |
| for (i = 0; i < ret; i++) { |
| if (cb->errors) |
| SetPageError(pages[i]); |
| end_page_writeback(pages[i]); |
| put_page(pages[i]); |
| } |
| nr_pages -= ret; |
| index += ret; |
| } |
| /* the inode may be gone now */ |
| } |
| |
| /* |
| * do the cleanup once all the compressed pages hit the disk. |
| * This will clear writeback on the file pages and free the compressed |
| * pages. |
| * |
| * This also calls the writeback end hooks for the file pages so that |
| * metadata and checksums can be updated in the file. |
| */ |
| static void end_compressed_bio_write(struct bio *bio) |
| { |
| struct extent_io_tree *tree; |
| struct compressed_bio *cb = bio->bi_private; |
| struct inode *inode; |
| struct page *page; |
| unsigned long index; |
| |
| if (bio->bi_status) |
| cb->errors = 1; |
| |
| /* if there are more bios still pending for this compressed |
| * extent, just exit |
| */ |
| if (!refcount_dec_and_test(&cb->pending_bios)) |
| goto out; |
| |
| /* ok, we're the last bio for this extent, step one is to |
| * call back into the FS and do all the end_io operations |
| */ |
| inode = cb->inode; |
| tree = &BTRFS_I(inode)->io_tree; |
| cb->compressed_pages[0]->mapping = cb->inode->i_mapping; |
| tree->ops->writepage_end_io_hook(cb->compressed_pages[0], |
| cb->start, |
| cb->start + cb->len - 1, |
| NULL, |
| bio->bi_status ? |
| BLK_STS_OK : BLK_STS_NOTSUPP); |
| cb->compressed_pages[0]->mapping = NULL; |
| |
| end_compressed_writeback(inode, cb); |
| /* note, our inode could be gone now */ |
| |
| /* |
| * release the compressed pages, these came from alloc_page and |
| * are not attached to the inode at all |
| */ |
| index = 0; |
| for (index = 0; index < cb->nr_pages; index++) { |
| page = cb->compressed_pages[index]; |
| page->mapping = NULL; |
| put_page(page); |
| } |
| |
| /* finally free the cb struct */ |
| kfree(cb->compressed_pages); |
| kfree(cb); |
| out: |
| bio_put(bio); |
| } |
| |
| /* |
| * worker function to build and submit bios for previously compressed pages. |
| * The corresponding pages in the inode should be marked for writeback |
| * and the compressed pages should have a reference on them for dropping |
| * when the IO is complete. |
| * |
| * This also checksums the file bytes and gets things ready for |
| * the end io hooks. |
| */ |
| blk_status_t btrfs_submit_compressed_write(struct inode *inode, u64 start, |
| unsigned long len, u64 disk_start, |
| unsigned long compressed_len, |
| struct page **compressed_pages, |
| unsigned long nr_pages) |
| { |
| struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb); |
| struct bio *bio = NULL; |
| struct compressed_bio *cb; |
| unsigned long bytes_left; |
| struct extent_io_tree *io_tree = &BTRFS_I(inode)->io_tree; |
| int pg_index = 0; |
| struct page *page; |
| u64 first_byte = disk_start; |
| struct block_device *bdev; |
| blk_status_t ret; |
| int skip_sum = BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM; |
| |
| WARN_ON(start & ((u64)PAGE_SIZE - 1)); |
| cb = kmalloc(compressed_bio_size(fs_info, compressed_len), GFP_NOFS); |
| if (!cb) |
| return BLK_STS_RESOURCE; |
| refcount_set(&cb->pending_bios, 0); |
| cb->errors = 0; |
| cb->inode = inode; |
| cb->start = start; |
| cb->len = len; |
| cb->mirror_num = 0; |
| cb->compressed_pages = compressed_pages; |
| cb->compressed_len = compressed_len; |
| cb->orig_bio = NULL; |
| cb->nr_pages = nr_pages; |
| |
| bdev = fs_info->fs_devices->latest_bdev; |
| |
| bio = btrfs_bio_alloc(bdev, first_byte); |
| bio_set_op_attrs(bio, REQ_OP_WRITE, 0); |
| bio->bi_private = cb; |
| bio->bi_end_io = end_compressed_bio_write; |
| refcount_set(&cb->pending_bios, 1); |
| |
| /* create and submit bios for the compressed pages */ |
| bytes_left = compressed_len; |
| for (pg_index = 0; pg_index < cb->nr_pages; pg_index++) { |
| int submit = 0; |
| |
| page = compressed_pages[pg_index]; |
| page->mapping = inode->i_mapping; |
| if (bio->bi_iter.bi_size) |
| submit = io_tree->ops->merge_bio_hook(page, 0, |
| PAGE_SIZE, |
| bio, 0); |
| |
| page->mapping = NULL; |
| if (submit || bio_add_page(bio, page, PAGE_SIZE, 0) < |
| PAGE_SIZE) { |
| bio_get(bio); |
| |
| /* |
| * inc the count before we submit the bio so |
| * we know the end IO handler won't happen before |
| * we inc the count. Otherwise, the cb might get |
| * freed before we're done setting it up |
| */ |
| refcount_inc(&cb->pending_bios); |
| ret = btrfs_bio_wq_end_io(fs_info, bio, |
| BTRFS_WQ_ENDIO_DATA); |
| BUG_ON(ret); /* -ENOMEM */ |
| |
| if (!skip_sum) { |
| ret = btrfs_csum_one_bio(inode, bio, start, 1); |
| BUG_ON(ret); /* -ENOMEM */ |
| } |
| |
| ret = btrfs_map_bio(fs_info, bio, 0, 1); |
| if (ret) { |
| bio->bi_status = ret; |
| bio_endio(bio); |
| } |
| |
| bio_put(bio); |
| |
| bio = btrfs_bio_alloc(bdev, first_byte); |
| bio_set_op_attrs(bio, REQ_OP_WRITE, 0); |
| bio->bi_private = cb; |
| bio->bi_end_io = end_compressed_bio_write; |
| bio_add_page(bio, page, PAGE_SIZE, 0); |
| } |
| if (bytes_left < PAGE_SIZE) { |
| btrfs_info(fs_info, |
| "bytes left %lu compress len %lu nr %lu", |
| bytes_left, cb->compressed_len, cb->nr_pages); |
| } |
| bytes_left -= PAGE_SIZE; |
| first_byte += PAGE_SIZE; |
| cond_resched(); |
| } |
| bio_get(bio); |
| |
| ret = btrfs_bio_wq_end_io(fs_info, bio, BTRFS_WQ_ENDIO_DATA); |
| BUG_ON(ret); /* -ENOMEM */ |
| |
| if (!skip_sum) { |
| ret = btrfs_csum_one_bio(inode, bio, start, 1); |
| BUG_ON(ret); /* -ENOMEM */ |
| } |
| |
| ret = btrfs_map_bio(fs_info, bio, 0, 1); |
| if (ret) { |
| bio->bi_status = ret; |
| bio_endio(bio); |
| } |
| |
| bio_put(bio); |
| return 0; |
| } |
| |
| static u64 bio_end_offset(struct bio *bio) |
| { |
| struct bio_vec *last = &bio->bi_io_vec[bio->bi_vcnt - 1]; |
| |
| return page_offset(last->bv_page) + last->bv_len + last->bv_offset; |
| } |
| |
| static noinline int add_ra_bio_pages(struct inode *inode, |
| u64 compressed_end, |
| struct compressed_bio *cb) |
| { |
| unsigned long end_index; |
| unsigned long pg_index; |
| u64 last_offset; |
| u64 isize = i_size_read(inode); |
| int ret; |
| struct page *page; |
| unsigned long nr_pages = 0; |
| struct extent_map *em; |
| struct address_space *mapping = inode->i_mapping; |
| struct extent_map_tree *em_tree; |
| struct extent_io_tree *tree; |
| u64 end; |
| int misses = 0; |
| |
| last_offset = bio_end_offset(cb->orig_bio); |
| em_tree = &BTRFS_I(inode)->extent_tree; |
| tree = &BTRFS_I(inode)->io_tree; |
| |
| if (isize == 0) |
| return 0; |
| |
| end_index = (i_size_read(inode) - 1) >> PAGE_SHIFT; |
| |
| while (last_offset < compressed_end) { |
| pg_index = last_offset >> PAGE_SHIFT; |
| |
| if (pg_index > end_index) |
| break; |
| |
| rcu_read_lock(); |
| page = radix_tree_lookup(&mapping->page_tree, pg_index); |
| rcu_read_unlock(); |
| if (page && !radix_tree_exceptional_entry(page)) { |
| misses++; |
| if (misses > 4) |
| break; |
| goto next; |
| } |
| |
| page = __page_cache_alloc(mapping_gfp_constraint(mapping, |
| ~__GFP_FS)); |
| if (!page) |
| break; |
| |
| if (add_to_page_cache_lru(page, mapping, pg_index, GFP_NOFS)) { |
| put_page(page); |
| goto next; |
| } |
| |
| end = last_offset + PAGE_SIZE - 1; |
| /* |
| * at this point, we have a locked page in the page cache |
| * for these bytes in the file. But, we have to make |
| * sure they map to this compressed extent on disk. |
| */ |
| set_page_extent_mapped(page); |
| lock_extent(tree, last_offset, end); |
| read_lock(&em_tree->lock); |
| em = lookup_extent_mapping(em_tree, last_offset, |
| PAGE_SIZE); |
| read_unlock(&em_tree->lock); |
| |
| if (!em || last_offset < em->start || |
| (last_offset + PAGE_SIZE > extent_map_end(em)) || |
| (em->block_start >> 9) != cb->orig_bio->bi_iter.bi_sector) { |
| free_extent_map(em); |
| unlock_extent(tree, last_offset, end); |
| unlock_page(page); |
| put_page(page); |
| break; |
| } |
| free_extent_map(em); |
| |
| if (page->index == end_index) { |
| char *userpage; |
| size_t zero_offset = isize & (PAGE_SIZE - 1); |
| |
| if (zero_offset) { |
| int zeros; |
| zeros = PAGE_SIZE - zero_offset; |
| userpage = kmap_atomic(page); |
| memset(userpage + zero_offset, 0, zeros); |
| flush_dcache_page(page); |
| kunmap_atomic(userpage); |
| } |
| } |
| |
| ret = bio_add_page(cb->orig_bio, page, |
| PAGE_SIZE, 0); |
| |
| if (ret == PAGE_SIZE) { |
| nr_pages++; |
| put_page(page); |
| } else { |
| unlock_extent(tree, last_offset, end); |
| unlock_page(page); |
| put_page(page); |
| break; |
| } |
| next: |
| last_offset += PAGE_SIZE; |
| } |
| return 0; |
| } |
| |
| /* |
| * for a compressed read, the bio we get passed has all the inode pages |
| * in it. We don't actually do IO on those pages but allocate new ones |
| * to hold the compressed pages on disk. |
| * |
| * bio->bi_iter.bi_sector points to the compressed extent on disk |
| * bio->bi_io_vec points to all of the inode pages |
| * |
| * After the compressed pages are read, we copy the bytes into the |
| * bio we were passed and then call the bio end_io calls |
| */ |
| blk_status_t btrfs_submit_compressed_read(struct inode *inode, struct bio *bio, |
| int mirror_num, unsigned long bio_flags) |
| { |
| struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb); |
| struct extent_io_tree *tree; |
| struct extent_map_tree *em_tree; |
| struct compressed_bio *cb; |
| unsigned long compressed_len; |
| unsigned long nr_pages; |
| unsigned long pg_index; |
| struct page *page; |
| struct block_device *bdev; |
| struct bio *comp_bio; |
| u64 cur_disk_byte = (u64)bio->bi_iter.bi_sector << 9; |
| u64 em_len; |
| u64 em_start; |
| struct extent_map *em; |
| blk_status_t ret = BLK_STS_RESOURCE; |
| int faili = 0; |
| u32 *sums; |
| |
| tree = &BTRFS_I(inode)->io_tree; |
| em_tree = &BTRFS_I(inode)->extent_tree; |
| |
| /* we need the actual starting offset of this extent in the file */ |
| read_lock(&em_tree->lock); |
| em = lookup_extent_mapping(em_tree, |
| page_offset(bio->bi_io_vec->bv_page), |
| PAGE_SIZE); |
| read_unlock(&em_tree->lock); |
| if (!em) |
| return BLK_STS_IOERR; |
| |
| compressed_len = em->block_len; |
| cb = kmalloc(compressed_bio_size(fs_info, compressed_len), GFP_NOFS); |
| if (!cb) |
| goto out; |
| |
| refcount_set(&cb->pending_bios, 0); |
| cb->errors = 0; |
| cb->inode = inode; |
| cb->mirror_num = mirror_num; |
| sums = &cb->sums; |
| |
| cb->start = em->orig_start; |
| em_len = em->len; |
| em_start = em->start; |
| |
| free_extent_map(em); |
| em = NULL; |
| |
| cb->len = bio->bi_iter.bi_size; |
| cb->compressed_len = compressed_len; |
| cb->compress_type = extent_compress_type(bio_flags); |
| cb->orig_bio = bio; |
| |
| nr_pages = DIV_ROUND_UP(compressed_len, PAGE_SIZE); |
| cb->compressed_pages = kcalloc(nr_pages, sizeof(struct page *), |
| GFP_NOFS); |
| if (!cb->compressed_pages) |
| goto fail1; |
| |
| bdev = fs_info->fs_devices->latest_bdev; |
| |
| for (pg_index = 0; pg_index < nr_pages; pg_index++) { |
| cb->compressed_pages[pg_index] = alloc_page(GFP_NOFS | |
| __GFP_HIGHMEM); |
| if (!cb->compressed_pages[pg_index]) { |
| faili = pg_index - 1; |
| ret = BLK_STS_RESOURCE; |
| goto fail2; |
| } |
| } |
| faili = nr_pages - 1; |
| cb->nr_pages = nr_pages; |
| |
| add_ra_bio_pages(inode, em_start + em_len, cb); |
| |
| /* include any pages we added in add_ra-bio_pages */ |
| cb->len = bio->bi_iter.bi_size; |
| |
| comp_bio = btrfs_bio_alloc(bdev, cur_disk_byte); |
| bio_set_op_attrs (comp_bio, REQ_OP_READ, 0); |
| comp_bio->bi_private = cb; |
| comp_bio->bi_end_io = end_compressed_bio_read; |
| refcount_set(&cb->pending_bios, 1); |
| |
| for (pg_index = 0; pg_index < nr_pages; pg_index++) { |
| int submit = 0; |
| |
| page = cb->compressed_pages[pg_index]; |
| page->mapping = inode->i_mapping; |
| page->index = em_start >> PAGE_SHIFT; |
| |
| if (comp_bio->bi_iter.bi_size) |
| submit = tree->ops->merge_bio_hook(page, 0, |
| PAGE_SIZE, |
| comp_bio, 0); |
| |
| page->mapping = NULL; |
| if (submit || bio_add_page(comp_bio, page, PAGE_SIZE, 0) < |
| PAGE_SIZE) { |
| bio_get(comp_bio); |
| |
| ret = btrfs_bio_wq_end_io(fs_info, comp_bio, |
| BTRFS_WQ_ENDIO_DATA); |
| BUG_ON(ret); /* -ENOMEM */ |
| |
| /* |
| * inc the count before we submit the bio so |
| * we know the end IO handler won't happen before |
| * we inc the count. Otherwise, the cb might get |
| * freed before we're done setting it up |
| */ |
| refcount_inc(&cb->pending_bios); |
| |
| if (!(BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM)) { |
| ret = btrfs_lookup_bio_sums(inode, comp_bio, |
| sums); |
| BUG_ON(ret); /* -ENOMEM */ |
| } |
| sums += DIV_ROUND_UP(comp_bio->bi_iter.bi_size, |
| fs_info->sectorsize); |
| |
| ret = btrfs_map_bio(fs_info, comp_bio, mirror_num, 0); |
| if (ret) { |
| comp_bio->bi_status = ret; |
| bio_endio(comp_bio); |
| } |
| |
| bio_put(comp_bio); |
| |
| comp_bio = btrfs_bio_alloc(bdev, cur_disk_byte); |
| bio_set_op_attrs(comp_bio, REQ_OP_READ, 0); |
| comp_bio->bi_private = cb; |
| comp_bio->bi_end_io = end_compressed_bio_read; |
| |
| bio_add_page(comp_bio, page, PAGE_SIZE, 0); |
| } |
| cur_disk_byte += PAGE_SIZE; |
| } |
| bio_get(comp_bio); |
| |
| ret = btrfs_bio_wq_end_io(fs_info, comp_bio, BTRFS_WQ_ENDIO_DATA); |
| BUG_ON(ret); /* -ENOMEM */ |
| |
| if (!(BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM)) { |
| ret = btrfs_lookup_bio_sums(inode, comp_bio, sums); |
| BUG_ON(ret); /* -ENOMEM */ |
| } |
| |
| ret = btrfs_map_bio(fs_info, comp_bio, mirror_num, 0); |
| if (ret) { |
| comp_bio->bi_status = ret; |
| bio_endio(comp_bio); |
| } |
| |
| bio_put(comp_bio); |
| return 0; |
| |
| fail2: |
| while (faili >= 0) { |
| __free_page(cb->compressed_pages[faili]); |
| faili--; |
| } |
| |
| kfree(cb->compressed_pages); |
| fail1: |
| kfree(cb); |
| out: |
| free_extent_map(em); |
| return ret; |
| } |
| |
| /* |
| * Heuristic uses systematic sampling to collect data from the input data |
| * range, the logic can be tuned by the following constants: |
| * |
| * @SAMPLING_READ_SIZE - how many bytes will be copied from for each sample |
| * @SAMPLING_INTERVAL - range from which the sampled data can be collected |
| */ |
| #define SAMPLING_READ_SIZE (16) |
| #define SAMPLING_INTERVAL (256) |
| |
| /* |
| * For statistical analysis of the input data we consider bytes that form a |
| * Galois Field of 256 objects. Each object has an attribute count, ie. how |
| * many times the object appeared in the sample. |
| */ |
| #define BUCKET_SIZE (256) |
| |
| /* |
| * The size of the sample is based on a statistical sampling rule of thumb. |
| * The common way is to perform sampling tests as long as the number of |
| * elements in each cell is at least 5. |
| * |
| * Instead of 5, we choose 32 to obtain more accurate results. |
| * If the data contain the maximum number of symbols, which is 256, we obtain a |
| * sample size bound by 8192. |
| * |
| * For a sample of at most 8KB of data per data range: 16 consecutive bytes |
| * from up to 512 locations. |
| */ |
| #define MAX_SAMPLE_SIZE (BTRFS_MAX_UNCOMPRESSED * \ |
| SAMPLING_READ_SIZE / SAMPLING_INTERVAL) |
| |
| struct bucket_item { |
| u32 count; |
| }; |
| |
| struct heuristic_ws { |
| /* Partial copy of input data */ |
| u8 *sample; |
| u32 sample_size; |
| /* Buckets store counters for each byte value */ |
| struct bucket_item *bucket; |
| struct list_head list; |
| }; |
| |
| 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); |
| } |
| |
| static struct list_head *alloc_heuristic_ws(void) |
| { |
| 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; |
| |
| INIT_LIST_HEAD(&ws->list); |
| return &ws->list; |
| fail: |
| free_heuristic_ws(&ws->list); |
| return ERR_PTR(-ENOMEM); |
| } |
| |
| struct workspaces_list { |
| struct list_head idle_ws; |
| spinlock_t ws_lock; |
| /* Number of free workspaces */ |
| int free_ws; |
| /* Total number of allocated workspaces */ |
| atomic_t total_ws; |
| /* Waiters for a free workspace */ |
| wait_queue_head_t ws_wait; |
| }; |
| |
| static struct workspaces_list btrfs_comp_ws[BTRFS_COMPRESS_TYPES]; |
| |
| static struct workspaces_list btrfs_heuristic_ws; |
| |
| static const struct btrfs_compress_op * const btrfs_compress_op[] = { |
| &btrfs_zlib_compress, |
| &btrfs_lzo_compress, |
| &btrfs_zstd_compress, |
| }; |
| |
| void __init btrfs_init_compress(void) |
| { |
| struct list_head *workspace; |
| int i; |
| |
| INIT_LIST_HEAD(&btrfs_heuristic_ws.idle_ws); |
| spin_lock_init(&btrfs_heuristic_ws.ws_lock); |
| atomic_set(&btrfs_heuristic_ws.total_ws, 0); |
| init_waitqueue_head(&btrfs_heuristic_ws.ws_wait); |
| |
| workspace = alloc_heuristic_ws(); |
| if (IS_ERR(workspace)) { |
| pr_warn( |
| "BTRFS: cannot preallocate heuristic workspace, will try later\n"); |
| } else { |
| atomic_set(&btrfs_heuristic_ws.total_ws, 1); |
| btrfs_heuristic_ws.free_ws = 1; |
| list_add(workspace, &btrfs_heuristic_ws.idle_ws); |
| } |
| |
| for (i = 0; i < BTRFS_COMPRESS_TYPES; i++) { |
| INIT_LIST_HEAD(&btrfs_comp_ws[i].idle_ws); |
| spin_lock_init(&btrfs_comp_ws[i].ws_lock); |
| atomic_set(&btrfs_comp_ws[i].total_ws, 0); |
| init_waitqueue_head(&btrfs_comp_ws[i].ws_wait); |
| |
| /* |
| * Preallocate one workspace for each compression type so |
| * we can guarantee forward progress in the worst case |
| */ |
| workspace = btrfs_compress_op[i]->alloc_workspace(); |
| if (IS_ERR(workspace)) { |
| pr_warn("BTRFS: cannot preallocate compression workspace, will try later\n"); |
| } else { |
| atomic_set(&btrfs_comp_ws[i].total_ws, 1); |
| btrfs_comp_ws[i].free_ws = 1; |
| list_add(workspace, &btrfs_comp_ws[i].idle_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. |
| */ |
| static struct list_head *__find_workspace(int type, bool heuristic) |
| { |
| struct list_head *workspace; |
| int cpus = num_online_cpus(); |
| int idx = type - 1; |
| 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; |
| |
| if (heuristic) { |
| idle_ws = &btrfs_heuristic_ws.idle_ws; |
| ws_lock = &btrfs_heuristic_ws.ws_lock; |
| total_ws = &btrfs_heuristic_ws.total_ws; |
| ws_wait = &btrfs_heuristic_ws.ws_wait; |
| free_ws = &btrfs_heuristic_ws.free_ws; |
| } else { |
| idle_ws = &btrfs_comp_ws[idx].idle_ws; |
| ws_lock = &btrfs_comp_ws[idx].ws_lock; |
| total_ws = &btrfs_comp_ws[idx].total_ws; |
| ws_wait = &btrfs_comp_ws[idx].ws_wait; |
| free_ws = &btrfs_comp_ws[idx].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(); |
| if (heuristic) |
| workspace = alloc_heuristic_ws(); |
| else |
| workspace = btrfs_compress_op[idx]->alloc_workspace(); |
| 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 *find_workspace(int type) |
| { |
| return __find_workspace(type, false); |
| } |
| |
| /* |
| * put a workspace struct back on the list or free it if we have enough |
| * idle ones sitting around |
| */ |
| static void __free_workspace(int type, struct list_head *workspace, |
| bool heuristic) |
| { |
| int idx = type - 1; |
| struct list_head *idle_ws; |
| spinlock_t *ws_lock; |
| atomic_t *total_ws; |
| wait_queue_head_t *ws_wait; |
| int *free_ws; |
| |
| if (heuristic) { |
| idle_ws = &btrfs_heuristic_ws.idle_ws; |
| ws_lock = &btrfs_heuristic_ws.ws_lock; |
| total_ws = &btrfs_heuristic_ws.total_ws; |
| ws_wait = &btrfs_heuristic_ws.ws_wait; |
| free_ws = &btrfs_heuristic_ws.free_ws; |
| } else { |
| idle_ws = &btrfs_comp_ws[idx].idle_ws; |
| ws_lock = &btrfs_comp_ws[idx].ws_lock; |
| total_ws = &btrfs_comp_ws[idx].total_ws; |
| ws_wait = &btrfs_comp_ws[idx].ws_wait; |
| free_ws = &btrfs_comp_ws[idx].free_ws; |
| } |
| |
| spin_lock(ws_lock); |
| if (*free_ws <= num_online_cpus()) { |
| list_add(workspace, idle_ws); |
| (*free_ws)++; |
| spin_unlock(ws_lock); |
| goto wake; |
| } |
| spin_unlock(ws_lock); |
| |
| if (heuristic) |
| free_heuristic_ws(workspace); |
| else |
| btrfs_compress_op[idx]->free_workspace(workspace); |
| atomic_dec(total_ws); |
| wake: |
| /* |
| * Make sure counter is updated before we wake up waiters. |
| */ |
| smp_mb(); |
| if (waitqueue_active(ws_wait)) |
| wake_up(ws_wait); |
| } |
| |
| static void free_workspace(int type, struct list_head *ws) |
| { |
| return __free_workspace(type, ws, false); |
| } |
| |
| /* |
| * cleanup function for module exit |
| */ |
| static void free_workspaces(void) |
| { |
| struct list_head *workspace; |
| int i; |
| |
| while (!list_empty(&btrfs_heuristic_ws.idle_ws)) { |
| workspace = btrfs_heuristic_ws.idle_ws.next; |
| list_del(workspace); |
| free_heuristic_ws(workspace); |
| atomic_dec(&btrfs_heuristic_ws.total_ws); |
| } |
| |
| for (i = 0; i < BTRFS_COMPRESS_TYPES; i++) { |
| while (!list_empty(&btrfs_comp_ws[i].idle_ws)) { |
| workspace = btrfs_comp_ws[i].idle_ws.next; |
| list_del(workspace); |
| btrfs_compress_op[i]->free_workspace(workspace); |
| atomic_dec(&btrfs_comp_ws[i].total_ws); |
| } |
| } |
| } |
| |
| /* |
| * Given an address space and start and length, compress the bytes into @pages |
| * that are allocated on demand. |
| * |
| * @type_level is encoded algorithm and level, where level 0 means whatever |
| * default the algorithm chooses and is opaque here; |
| * - compression algo are 0-3 |
| * - the level are bits 4-7 |
| * |
| * @out_pages is an in/out parameter, holds maximum number of pages to allocate |
| * and returns number of actually allocated pages |
| * |
| * @total_in is used to return the number of bytes actually read. It |
| * may be smaller than the input length if we had to exit early because we |
| * ran out of room in the pages array or because we cross the |
| * max_out threshold. |
| * |
| * @total_out is an in/out parameter, must be set to the input length and will |
| * be also used to return the total number of compressed bytes |
| * |
| * @max_out tells us the max number of bytes that we're allowed to |
| * stuff into pages |
| */ |
| int btrfs_compress_pages(unsigned int type_level, struct address_space *mapping, |
| u64 start, struct page **pages, |
| unsigned long *out_pages, |
| unsigned long *total_in, |
| unsigned long *total_out) |
| { |
| struct list_head *workspace; |
| int ret; |
| int type = type_level & 0xF; |
| |
| workspace = find_workspace(type); |
| |
| btrfs_compress_op[type - 1]->set_level(workspace, type_level); |
| ret = btrfs_compress_op[type-1]->compress_pages(workspace, mapping, |
| start, pages, |
| out_pages, |
| total_in, total_out); |
| free_workspace(type, workspace); |
| return ret; |
| } |
| |
| /* |
| * pages_in is an array of pages with compressed data. |
| * |
| * disk_start is the starting logical offset of this array in the file |
| * |
| * orig_bio contains the pages from the file that we want to decompress into |
| * |
| * srclen is the number of bytes in pages_in |
| * |
| * The basic idea is that we have a bio that was created by readpages. |
| * The pages in the bio are for the uncompressed data, and they may not |
| * be contiguous. They all correspond to the range of bytes covered by |
| * the compressed extent. |
| */ |
| static int btrfs_decompress_bio(struct compressed_bio *cb) |
| { |
| struct list_head *workspace; |
| int ret; |
| int type = cb->compress_type; |
| |
| workspace = find_workspace(type); |
| ret = btrfs_compress_op[type - 1]->decompress_bio(workspace, cb); |
| free_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 = find_workspace(type); |
| |
| ret = btrfs_compress_op[type-1]->decompress(workspace, data_in, |
| dest_page, start_byte, |
| srclen, destlen); |
| |
| free_workspace(type, workspace); |
| return ret; |
| } |
| |
| void btrfs_exit_compress(void) |
| { |
| free_workspaces(); |
| } |
| |
| /* |
| * Copy uncompressed data from working buffer to pages. |
| * |
| * buf_start is the byte offset we're of the start of our workspace buffer. |
| * |
| * total_out is the last byte of the buffer |
| */ |
| int btrfs_decompress_buf2page(const char *buf, unsigned long buf_start, |
| unsigned long total_out, u64 disk_start, |
| struct bio *bio) |
| { |
| unsigned long buf_offset; |
| unsigned long current_buf_start; |
| unsigned long start_byte; |
| unsigned long prev_start_byte; |
| unsigned long working_bytes = total_out - buf_start; |
| unsigned long bytes; |
| char *kaddr; |
| struct bio_vec bvec = bio_iter_iovec(bio, bio->bi_iter); |
| |
| /* |
| * start byte is the first byte of the page we're currently |
| * copying into relative to the start of the compressed data. |
| */ |
| start_byte = page_offset(bvec.bv_page) - disk_start; |
| |
| /* we haven't yet hit data corresponding to this page */ |
| if (total_out <= start_byte) |
| return 1; |
| |
| /* |
| * the start of the data we care about is offset into |
| * the middle of our working buffer |
| */ |
| if (total_out > start_byte && buf_start < start_byte) { |
| buf_offset = start_byte - buf_start; |
| working_bytes -= buf_offset; |
| } else { |
| buf_offset = 0; |
| } |
| current_buf_start = buf_start; |
| |
| /* copy bytes from the working buffer into the pages */ |
| while (working_bytes > 0) { |
| bytes = min_t(unsigned long, bvec.bv_len, |
| PAGE_SIZE - buf_offset); |
| bytes = min(bytes, working_bytes); |
| |
| kaddr = kmap_atomic(bvec.bv_page); |
| memcpy(kaddr + bvec.bv_offset, buf + buf_offset, bytes); |
| kunmap_atomic(kaddr); |
| flush_dcache_page(bvec.bv_page); |
| |
| buf_offset += bytes; |
| working_bytes -= bytes; |
| current_buf_start += bytes; |
| |
| /* check if we need to pick another page */ |
| bio_advance(bio, bytes); |
| if (!bio->bi_iter.bi_size) |
| return 0; |
| bvec = bio_iter_iovec(bio, bio->bi_iter); |
| prev_start_byte = start_byte; |
| start_byte = page_offset(bvec.bv_page) - disk_start; |
| |
| /* |
| * We need to make sure we're only adjusting |
| * our offset into compression working buffer when |
| * we're switching pages. Otherwise we can incorrectly |
| * keep copying when we were actually done. |
| */ |
| if (start_byte != prev_start_byte) { |
| /* |
| * make sure our new page is covered by this |
| * working buffer |
| */ |
| if (total_out <= start_byte) |
| return 1; |
| |
| /* |
| * the next page in the biovec might not be adjacent |
| * to the last page, but it might still be found |
| * inside this working buffer. bump our offset pointer |
| */ |
| if (total_out > start_byte && |
| current_buf_start < start_byte) { |
| buf_offset = start_byte - buf_start; |
| working_bytes = total_out - start_byte; |
| current_buf_start = buf_start + buf_offset; |
| } |
| } |
| } |
| |
| return 1; |
| } |
| |
| /* |
| * Shannon Entropy calculation |
| * |
| * Pure byte distribution analysis fails to determine compressiability 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; |
| } |
| |
| /* Compare buckets by size, ascending */ |
| static int bucket_comp_rev(const void *lv, const void *rv) |
| { |
| const struct bucket_item *l = (const struct bucket_item *)lv; |
| const struct bucket_item *r = (const struct bucket_item *)rv; |
| |
| return r->count - l->count; |
| } |
| |
| /* |
| * 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 */ |
| sort(bucket, BUCKET_SIZE, sizeof(*bucket), &bucket_comp_rev, NULL); |
| |
| for (i = 0; i < BYTE_CORE_SET_LOW; i++) |
| coreset_sum += bucket[i].count; |
| |
| if (coreset_sum > core_set_threshold) |
| return i; |
| |
| for (; i < BYTE_CORE_SET_HIGH && bucket[i].count > 0; i++) { |
| coreset_sum += bucket[i].count; |
| if (coreset_sum > core_set_threshold) |
| break; |
| } |
| |
| return i; |
| } |
| |
| /* |
| * Count byte values in buckets. |
| * This heuristic can detect textual data (configs, xml, json, html, etc). |
| * Because in most text-like data byte set is restricted to limited number of |
| * possible characters, and that restriction in most cases makes data easy to |
| * compress. |
| * |
| * @BYTE_SET_THRESHOLD - consider all data within this byte set size: |
| * less - compressible |
| * more - need additional analysis |
| */ |
| #define BYTE_SET_THRESHOLD (64) |
| |
| static u32 byte_set_size(const struct heuristic_ws *ws) |
| { |
| u32 i; |
| u32 byte_set_size = 0; |
| |
| for (i = 0; i < BYTE_SET_THRESHOLD; i++) { |
| if (ws->bucket[i].count > 0) |
| byte_set_size++; |
| } |
| |
| /* |
| * Continue collecting count of byte values in buckets. If the byte |
| * set size is bigger then the threshold, it's pointless to continue, |
| * the detection technique would fail for this type of data. |
| */ |
| for (; i < BUCKET_SIZE; i++) { |
| if (ws->bucket[i].count > 0) { |
| byte_set_size++; |
| if (byte_set_size > BYTE_SET_THRESHOLD) |
| return byte_set_size; |
| } |
| } |
| |
| return byte_set_size; |
| } |
| |
| static bool sample_repeated_patterns(struct heuristic_ws *ws) |
| { |
| const u32 half_of_sample = ws->sample_size / 2; |
| const u8 *data = ws->sample; |
| |
| return memcmp(&data[0], &data[half_of_sample], half_of_sample) == 0; |
| } |
| |
| static void heuristic_collect_sample(struct inode *inode, u64 start, u64 end, |
| struct heuristic_ws *ws) |
| { |
| struct page *page; |
| u64 index, index_end; |
| u32 i, curr_sample_pos; |
| u8 *in_data; |
| |
| /* |
| * Compression handles the input data by chunks of 128KiB |
| * (defined by BTRFS_MAX_UNCOMPRESSED) |
| * |
| * We do the same for the heuristic and loop over the whole range. |
| * |
| * MAX_SAMPLE_SIZE - calculated under assumption that heuristic will |
| * process no more than BTRFS_MAX_UNCOMPRESSED at a time. |
| */ |
| if (end - start > BTRFS_MAX_UNCOMPRESSED) |
| end = start + BTRFS_MAX_UNCOMPRESSED; |
| |
| index = start >> PAGE_SHIFT; |
| index_end = end >> PAGE_SHIFT; |
| |
| /* Don't miss unaligned end */ |
| if (!IS_ALIGNED(end, PAGE_SIZE)) |
| index_end++; |
| |
| curr_sample_pos = 0; |
| while (index < index_end) { |
| page = find_get_page(inode->i_mapping, index); |
| in_data = kmap(page); |
| /* Handle case where the start is not aligned to PAGE_SIZE */ |
| i = start % PAGE_SIZE; |
| while (i < PAGE_SIZE - SAMPLING_READ_SIZE) { |
| /* Don't sample any garbage from the last page */ |
| if (start > end - SAMPLING_READ_SIZE) |
| break; |
| memcpy(&ws->sample[curr_sample_pos], &in_data[i], |
| SAMPLING_READ_SIZE); |
| i += SAMPLING_INTERVAL; |
| start += SAMPLING_INTERVAL; |
| curr_sample_pos += SAMPLING_READ_SIZE; |
| } |
| kunmap(page); |
| put_page(page); |
| |
| index++; |
| } |
| |
| ws->sample_size = curr_sample_pos; |
| } |
| |
| /* |
| * Compression heuristic. |
| * |
| * For now is's a naive and optimistic 'return true', we'll extend the logic to |
| * quickly (compared to direct compression) detect data characteristics |
| * (compressible/uncompressible) to avoid wasting CPU time on uncompressible |
| * data. |
| * |
| * The following types of analysis can be performed: |
| * - detect mostly zero data |
| * - detect data with low "byte set" size (text, etc) |
| * - detect data with low/high "core byte" set |
| * |
| * Return non-zero if the compression should be done, 0 otherwise. |
| */ |
| int btrfs_compress_heuristic(struct inode *inode, u64 start, u64 end) |
| { |
| struct list_head *ws_list = __find_workspace(0, true); |
| 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: |
| __free_workspace(0, ws_list, true); |
| return ret; |
| } |
| |
| unsigned int btrfs_compress_str2level(const char *str) |
| { |
| if (strncmp(str, "zlib", 4) != 0) |
| return 0; |
| |
| /* Accepted form: zlib:1 up to zlib:9 and nothing left after the number */ |
| if (str[4] == ':' && '1' <= str[5] && str[5] <= '9' && str[6] == 0) |
| return str[5] - '0'; |
| |
| return 0; |
| } |