linux-stable/fs/btrfs/compression.c
Qu Wenruo 6275193ef1 btrfs: refactor btrfs_lookup_bio_sums to handle out-of-order bvecs
Refactor btrfs_lookup_bio_sums() by:

- Remove the @file_offset parameter
  There are two factors making the @file_offset parameter useless:

  * For csum lookup in csum tree, file offset makes no sense
    We only need disk_bytenr, which is unrelated to file_offset

  * page_offset (file offset) of each bvec is not contiguous.
    Pages can be added to the same bio as long as their on-disk bytenr
    is contiguous, meaning we could have pages at different file offsets
    in the same bio.

  Thus passing file_offset makes no sense any more.
  The only user of file_offset is for data reloc inode, we will use
  a new function, search_file_offset_in_bio(), to handle it.

- Extract the csum tree lookup into search_csum_tree()
  The new function will handle the csum search in csum tree.
  The return value is the same as btrfs_find_ordered_sum(), returning
  the number of found sectors which have checksum.

- Change how we do the main loop
  The only needed info from bio is:
  * the on-disk bytenr
  * the length

  After extracting the above info, we can do the search without bio
  at all, which makes the main loop much simpler:

	for (cur_disk_bytenr = orig_disk_bytenr;
	     cur_disk_bytenr < orig_disk_bytenr + orig_len;
	     cur_disk_bytenr += count * sectorsize) {

		/* Lookup csum tree */
		count = search_csum_tree(fs_info, path, cur_disk_bytenr,
					 search_len, csum_dst);
		if (!count) {
			/* Csum hole handling */
		}
	}

- Use single variable as the source to calculate all other offsets
  Instead of all different type of variables, we use only one main
  variable, cur_disk_bytenr, which represents the current disk bytenr.

  All involved values can be calculated from that variable, and
  all those variable will only be visible in the inner loop.

The above refactoring makes btrfs_lookup_bio_sums() way more robust than
it used to be, especially related to the file offset lookup.  Now
file_offset lookup is only related to data reloc inode, otherwise we
don't need to bother file_offset at all.

Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
2020-12-09 19:16:11 +01:00

1719 lines
44 KiB
C

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