diff options
Diffstat (limited to 'fs/btrfs/compression.c')
| -rw-r--r-- | fs/btrfs/compression.c | 511 |
1 files changed, 480 insertions, 31 deletions
diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c index b51d23f5cafa..b35ce16b3df3 100644 --- a/fs/btrfs/compression.c +++ b/fs/btrfs/compression.c @@ -33,6 +33,8 @@ #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" @@ -107,7 +109,8 @@ static void end_compressed_bio_read(struct bio *bio) struct inode *inode; struct page *page; unsigned long index; - int ret; + unsigned int mirror = btrfs_io_bio(bio)->mirror_num; + int ret = 0; if (bio->bi_status) cb->errors = 1; @@ -118,6 +121,21 @@ static void end_compressed_bio_read(struct bio *bio) 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); @@ -239,7 +257,8 @@ static void end_compressed_bio_write(struct bio *bio) cb->start, cb->start + cb->len - 1, NULL, - bio->bi_status ? 0 : 1); + bio->bi_status ? + BLK_STS_OK : BLK_STS_NOTSUPP); cb->compressed_pages[0]->mapping = NULL; end_compressed_writeback(inode, cb); @@ -690,7 +709,86 @@ out: return ret; } -static struct { +/* + * 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 */ @@ -699,7 +797,11 @@ static struct { atomic_t total_ws; /* Waiters for a free workspace */ wait_queue_head_t ws_wait; -} btrfs_comp_ws[BTRFS_COMPRESS_TYPES]; +}; + +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, @@ -709,11 +811,25 @@ static const struct btrfs_compress_op * const btrfs_compress_op[] = { void __init btrfs_init_compress(void) { + struct list_head *workspace; int i; - for (i = 0; i < BTRFS_COMPRESS_TYPES; i++) { - struct list_head *workspace; + 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); @@ -740,18 +856,32 @@ void __init btrfs_init_compress(void) * Preallocation makes a forward progress guarantees and we do not return * errors. */ -static struct list_head *find_workspace(int type) +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; + } - struct list_head *idle_ws = &btrfs_comp_ws[idx].idle_ws; - spinlock_t *ws_lock = &btrfs_comp_ws[idx].ws_lock; - atomic_t *total_ws = &btrfs_comp_ws[idx].total_ws; - wait_queue_head_t *ws_wait = &btrfs_comp_ws[idx].ws_wait; - int *free_ws = &btrfs_comp_ws[idx].free_ws; again: spin_lock(ws_lock); if (!list_empty(idle_ws)) { @@ -781,7 +911,10 @@ again: * context of btrfs_compress_bio/btrfs_compress_pages */ nofs_flag = memalloc_nofs_save(); - workspace = btrfs_compress_op[idx]->alloc_workspace(); + if (heuristic) + workspace = alloc_heuristic_ws(); + else + workspace = btrfs_compress_op[idx]->alloc_workspace(); memalloc_nofs_restore(nofs_flag); if (IS_ERR(workspace)) { @@ -812,18 +945,38 @@ 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) +static void __free_workspace(int type, struct list_head *workspace, + bool heuristic) { int idx = type - 1; - struct list_head *idle_ws = &btrfs_comp_ws[idx].idle_ws; - spinlock_t *ws_lock = &btrfs_comp_ws[idx].ws_lock; - atomic_t *total_ws = &btrfs_comp_ws[idx].total_ws; - wait_queue_head_t *ws_wait = &btrfs_comp_ws[idx].ws_wait; - int *free_ws = &btrfs_comp_ws[idx].free_ws; + 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()) { @@ -834,7 +987,10 @@ static void free_workspace(int type, struct list_head *workspace) } spin_unlock(ws_lock); - btrfs_compress_op[idx]->free_workspace(workspace); + if (heuristic) + free_heuristic_ws(workspace); + else + btrfs_compress_op[idx]->free_workspace(workspace); atomic_dec(total_ws); wake: /* @@ -845,6 +1001,11 @@ wake: 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 */ @@ -853,6 +1014,13 @@ 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; @@ -867,6 +1035,11 @@ static void free_workspaces(void) * 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 * @@ -881,7 +1054,7 @@ static void free_workspaces(void) * @max_out tells us the max number of bytes that we're allowed to * stuff into pages */ -int btrfs_compress_pages(int type, struct address_space *mapping, +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, @@ -889,9 +1062,11 @@ int btrfs_compress_pages(int type, struct address_space *mapping, { 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, @@ -1050,6 +1225,211 @@ int btrfs_decompress_buf2page(const char *buf, unsigned long buf_start, } /* + * 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 @@ -1066,18 +1446,87 @@ int btrfs_decompress_buf2page(const char *buf, unsigned long buf_start, */ int btrfs_compress_heuristic(struct inode *inode, u64 start, u64 end) { - u64 index = start >> PAGE_SHIFT; - u64 end_index = end >> PAGE_SHIFT; - struct page *page; - int ret = 1; + struct list_head *ws_list = __find_workspace(0, true); + struct heuristic_ws *ws; + u32 i; + u8 byte; + int ret = 0; - while (index <= end_index) { - page = find_get_page(inode->i_mapping, index); - kmap(page); - kunmap(page); - put_page(page); - index++; + 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; +} |