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WSL2-Linux-Kernel
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WSL2-Linux-Kernel/fs/btrfs/compression.c

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50 KiB
C
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// 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/kthread.h>
#include <linux/time.h>
#include <linux/init.h>
#include <linux/string.h>
#include <linux/backing-dev.h>
#include <linux/writeback.h>
#include <linux/slab.h>
#include <linux/sched/mm.h>
#include <linux/log2.h>
#include <crypto/hash.h>
#include "misc.h"
#include "ctree.h"
#include "disk-io.h"
#include "transaction.h"
#include "btrfs_inode.h"
#include "volumes.h"
#include "ordered-data.h"
#include "compression.h"
#include "extent_io.h"
#include "extent_map.h"
#include "subpage.h"
#include "zoned.h"
static const char* const btrfs_compress_types[] = { "", "zlib", "lzo", "zstd" };
const char* btrfs_compress_type2str(enum btrfs_compression_type type)
{
switch (type) {
case BTRFS_COMPRESS_ZLIB:
case BTRFS_COMPRESS_LZO:
case BTRFS_COMPRESS_ZSTD:
case BTRFS_COMPRESS_NONE:
return btrfs_compress_types[type];
default:
break;
}
return NULL;
}
bool btrfs_compress_is_valid_type(const char *str, size_t len)
{
int i;
for (i = 1; i < ARRAY_SIZE(btrfs_compress_types); i++) {
size_t comp_len = strlen(btrfs_compress_types[i]);
if (len < comp_len)
continue;
if (!strncmp(btrfs_compress_types[i], str, comp_len))
return true;
}
return false;
}
static int compression_compress_pages(int type, struct list_head *ws,
struct address_space *mapping, u64 start, struct page **pages,
unsigned long *out_pages, unsigned long *total_in,
unsigned long *total_out)
{
switch (type) {
case BTRFS_COMPRESS_ZLIB:
return zlib_compress_pages(ws, mapping, start, pages,
out_pages, total_in, total_out);
case BTRFS_COMPRESS_LZO:
return lzo_compress_pages(ws, mapping, start, pages,
out_pages, total_in, total_out);
case BTRFS_COMPRESS_ZSTD:
return zstd_compress_pages(ws, mapping, start, pages,
out_pages, total_in, total_out);
case BTRFS_COMPRESS_NONE:
default:
/*
* This can happen when compression races with remount setting
* it to 'no compress', while caller doesn't call
* inode_need_compress() to check if we really need to
* compress.
*
* Not a big deal, just need to inform caller that we
* haven't allocated any pages yet.
*/
*out_pages = 0;
return -E2BIG;
}
}
static int compression_decompress_bio(struct list_head *ws,
struct compressed_bio *cb)
{
switch (cb->compress_type) {
case BTRFS_COMPRESS_ZLIB: return zlib_decompress_bio(ws, cb);
case BTRFS_COMPRESS_LZO: return lzo_decompress_bio(ws, cb);
case BTRFS_COMPRESS_ZSTD: return zstd_decompress_bio(ws, cb);
case BTRFS_COMPRESS_NONE:
default:
/*
* This can't happen, the type is validated several times
* before we get here.
*/
BUG();
}
}
static int compression_decompress(int type, struct list_head *ws,
unsigned char *data_in, struct page *dest_page,
unsigned long start_byte, size_t srclen, size_t destlen)
{
switch (type) {
case BTRFS_COMPRESS_ZLIB: return zlib_decompress(ws, data_in, dest_page,
start_byte, srclen, destlen);
case BTRFS_COMPRESS_LZO: return lzo_decompress(ws, data_in, dest_page,
start_byte, srclen, destlen);
case BTRFS_COMPRESS_ZSTD: return zstd_decompress(ws, data_in, dest_page,
start_byte, srclen, destlen);
case BTRFS_COMPRESS_NONE:
default:
/*
* This can't happen, the type is validated several times
* before we get here.
*/
BUG();
}
}
static int btrfs_decompress_bio(struct compressed_bio *cb);
static inline int compressed_bio_size(struct btrfs_fs_info *fs_info,
unsigned long disk_size)
{
return sizeof(struct compressed_bio) +
(DIV_ROUND_UP(disk_size, fs_info->sectorsize)) * fs_info->csum_size;
}
static int check_compressed_csum(struct btrfs_inode *inode, struct bio *bio,
u64 disk_start)
{
struct btrfs_fs_info *fs_info = inode->root->fs_info;
SHASH_DESC_ON_STACK(shash, fs_info->csum_shash);
const u32 csum_size = fs_info->csum_size;
const u32 sectorsize = fs_info->sectorsize;
struct page *page;
unsigned int i;
char *kaddr;
u8 csum[BTRFS_CSUM_SIZE];
struct compressed_bio *cb = bio->bi_private;
u8 *cb_sum = cb->sums;
if ((inode->flags & BTRFS_INODE_NODATASUM) ||
test_bit(BTRFS_FS_STATE_NO_CSUMS, &fs_info->fs_state))
return 0;
shash->tfm = fs_info->csum_shash;
for (i = 0; i < cb->nr_pages; i++) {
u32 pg_offset;
u32 bytes_left = PAGE_SIZE;
page = cb->compressed_pages[i];
/* Determine the remaining bytes inside the page first */
if (i == cb->nr_pages - 1)
bytes_left = cb->compressed_len - i * PAGE_SIZE;
/* Hash through the page sector by sector */
for (pg_offset = 0; pg_offset < bytes_left;
pg_offset += sectorsize) {
kaddr = kmap_atomic(page);
crypto_shash_digest(shash, kaddr + pg_offset,
sectorsize, csum);
kunmap_atomic(kaddr);
if (memcmp(&csum, cb_sum, csum_size) != 0) {
btrfs_print_data_csum_error(inode, disk_start,
csum, cb_sum, cb->mirror_num);
if (btrfs_bio(bio)->device)
btrfs_dev_stat_inc_and_print(
btrfs_bio(bio)->device,
BTRFS_DEV_STAT_CORRUPTION_ERRS);
return -EIO;
}
cb_sum += csum_size;
disk_start += sectorsize;
}
}
return 0;
}
/*
* Reduce bio and io accounting for a compressed_bio with its corresponding bio.
*
* Return true if there is no pending bio nor io.
* Return false otherwise.
*/
static bool dec_and_test_compressed_bio(struct compressed_bio *cb, struct bio *bio)
{
struct btrfs_fs_info *fs_info = btrfs_sb(cb->inode->i_sb);
unsigned int bi_size = 0;
bool last_io = false;
struct bio_vec *bvec;
struct bvec_iter_all iter_all;
/*
* At endio time, bi_iter.bi_size doesn't represent the real bio size.
* Thus here we have to iterate through all segments to grab correct
* bio size.
*/
bio_for_each_segment_all(bvec, bio, iter_all)
bi_size += bvec->bv_len;
if (bio->bi_status)
cb->status = bio->bi_status;
ASSERT(bi_size && bi_size <= cb->compressed_len);
last_io = refcount_sub_and_test(bi_size >> fs_info->sectorsize_bits,
&cb->pending_sectors);
/*
* Here we must wake up the possible error handler after all other
* operations on @cb finished, or we can race with
* finish_compressed_bio_*() which may free @cb.
*/
wake_up_var(cb);
return last_io;
}
static void finish_compressed_bio_read(struct compressed_bio *cb)
{
unsigned int index;
struct page *page;
/* Release the compressed pages */
for (index = 0; index < cb->nr_pages; index++) {
page = cb->compressed_pages[index];
page->mapping = NULL;
put_page(page);
}
/* Do io completion on the original bio */
if (cb->status != BLK_STS_OK) {
cb->orig_bio->bi_status = cb->status;
bio_endio(cb->orig_bio);
} else {
struct bio_vec *bvec;
struct bvec_iter_all iter_all;
/*
* We have verified the checksum already, set page checked so
* the end_io handlers know about it
*/
ASSERT(!bio_flagged(cb->orig_bio, BIO_CLONED));
bio_for_each_segment_all(bvec, cb->orig_bio, iter_all) {
u64 bvec_start = page_offset(bvec->bv_page) +
bvec->bv_offset;
btrfs_page_set_checked(btrfs_sb(cb->inode->i_sb),
bvec->bv_page, bvec_start,
bvec->bv_len);
}
bio_endio(cb->orig_bio);
}
/* Finally free the cb struct */
kfree(cb->compressed_pages);
kfree(cb);
}
/* when we finish reading compressed pages from the disk, we
* decompress them and then run the bio end_io routines on the
* decompressed pages (in the inode address space).
*
* This allows the checksumming and other IO error handling routines
* to work normally
*
* The compressed pages are freed here, and it must be run
* in process context
*/
static void end_compressed_bio_read(struct bio *bio)
{
struct compressed_bio *cb = bio->bi_private;
struct inode *inode;
unsigned int mirror = btrfs_bio(bio)->mirror_num;
int ret = 0;
if (!dec_and_test_compressed_bio(cb, bio))
goto out;
/*
* Record the correct mirror_num in cb->orig_bio so that
* read-repair can work properly.
*/
btrfs_bio(cb->orig_bio)->mirror_num = mirror;
cb->mirror_num = mirror;
/*
* Some IO in this cb have failed, just skip checksum as there
* is no way it could be correct.
*/
if (cb->status != BLK_STS_OK)
goto csum_failed;
inode = cb->inode;
ret = check_compressed_csum(BTRFS_I(inode), bio,
bio->bi_iter.bi_sector << 9);
if (ret)
goto csum_failed;
/* ok, we're the last bio for this extent, lets start
* the decompression.
*/
ret = btrfs_decompress_bio(cb);
csum_failed:
if (ret)
cb->status = errno_to_blk_status(ret);
finish_compressed_bio_read(cb);
out:
bio_put(bio);
}
/*
* Clear the writeback bits on all of the file
* pages for a compressed write
*/
static noinline void end_compressed_writeback(struct inode *inode,
const struct compressed_bio *cb)
{
struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
unsigned long index = cb->start >> PAGE_SHIFT;
unsigned long end_index = (cb->start + cb->len - 1) >> PAGE_SHIFT;
struct page *pages[16];
unsigned long nr_pages = end_index - index + 1;
const int errno = blk_status_to_errno(cb->status);
int i;
int ret;
if (errno)
mapping_set_error(inode->i_mapping, errno);
while (nr_pages > 0) {
ret = find_get_pages_contig(inode->i_mapping, index,
min_t(unsigned long,
nr_pages, ARRAY_SIZE(pages)), pages);
if (ret == 0) {
nr_pages -= 1;
index += 1;
continue;
}
for (i = 0; i < ret; i++) {
if (errno)
SetPageError(pages[i]);
btrfs_page_clamp_clear_writeback(fs_info, pages[i],
cb->start, cb->len);
put_page(pages[i]);
}
nr_pages -= ret;
index += ret;
}
/* the inode may be gone now */
}
static void finish_compressed_bio_write(struct compressed_bio *cb)
{
struct inode *inode = cb->inode;
unsigned int index;
/*
* Ok, we're the last bio for this extent, step one is to call back
* into the FS and do all the end_io operations.
*/
btrfs_writepage_endio_finish_ordered(BTRFS_I(inode), NULL,
cb->start, cb->start + cb->len - 1,
cb->status == BLK_STS_OK);
if (cb->writeback)
end_compressed_writeback(inode, cb);
/* Note, our inode could be gone now */
/*
* Release the compressed pages, these came from alloc_page and
* are not attached to the inode at all
*/
for (index = 0; index < cb->nr_pages; index++) {
struct page *page = cb->compressed_pages[index];
page->mapping = NULL;
put_page(page);
}
/* Finally free the cb struct */
kfree(cb->compressed_pages);
kfree(cb);
}
/*
* Do the cleanup once all the compressed pages hit the disk. This will clear
* writeback on the file pages and free the compressed pages.
*
* This also calls the writeback end hooks for the file pages so that metadata
* and checksums can be updated in the file.
*/
static void end_compressed_bio_write(struct bio *bio)
{
struct compressed_bio *cb = bio->bi_private;
if (!dec_and_test_compressed_bio(cb, bio))
goto out;
btrfs_record_physical_zoned(cb->inode, cb->start, bio);
finish_compressed_bio_write(cb);
out:
bio_put(bio);
}
static blk_status_t submit_compressed_bio(struct btrfs_fs_info *fs_info,
struct compressed_bio *cb,
struct bio *bio, int mirror_num)
{
blk_status_t ret;
ASSERT(bio->bi_iter.bi_size);
ret = btrfs_bio_wq_end_io(fs_info, bio, BTRFS_WQ_ENDIO_DATA);
if (ret)
return ret;
ret = btrfs_map_bio(fs_info, bio, mirror_num);
return ret;
}
/*
* Allocate a compressed_bio, which will be used to read/write on-disk
* (aka, compressed) * data.
*
* @cb: The compressed_bio structure, which records all the needed
* information to bind the compressed data to the uncompressed
* page cache.
* @disk_byten: The logical bytenr where the compressed data will be read
* from or written to.
* @endio_func: The endio function to call after the IO for compressed data
* is finished.
* @next_stripe_start: Return value of logical bytenr of where next stripe starts.
* Let the caller know to only fill the bio up to the stripe
* boundary.
*/
static struct bio *alloc_compressed_bio(struct compressed_bio *cb, u64 disk_bytenr,
unsigned int opf, bio_end_io_t endio_func,
u64 *next_stripe_start)
{
struct btrfs_fs_info *fs_info = btrfs_sb(cb->inode->i_sb);
struct btrfs_io_geometry geom;
struct extent_map *em;
struct bio *bio;
int ret;
bio = btrfs_bio_alloc(BIO_MAX_VECS);
bio->bi_iter.bi_sector = disk_bytenr >> SECTOR_SHIFT;
bio->bi_opf = opf;
bio->bi_private = cb;
bio->bi_end_io = endio_func;
em = btrfs_get_chunk_map(fs_info, disk_bytenr, fs_info->sectorsize);
if (IS_ERR(em)) {
bio_put(bio);
return ERR_CAST(em);
}
if (bio_op(bio) == REQ_OP_ZONE_APPEND)
bio_set_dev(bio, em->map_lookup->stripes[0].dev->bdev);
ret = btrfs_get_io_geometry(fs_info, em, btrfs_op(bio), disk_bytenr, &geom);
free_extent_map(em);
if (ret < 0) {
bio_put(bio);
return ERR_PTR(ret);
}
*next_stripe_start = disk_bytenr + geom.len;
return bio;
}
/*
* worker function to build and submit bios for previously compressed pages.
* The corresponding pages in the inode should be marked for writeback
* and the compressed pages should have a reference on them for dropping
* when the IO is complete.
*
* This also checksums the file bytes and gets things ready for
* the end io hooks.
*/
blk_status_t btrfs_submit_compressed_write(struct btrfs_inode *inode, u64 start,
unsigned int len, u64 disk_start,
unsigned int compressed_len,
struct page **compressed_pages,
unsigned int nr_pages,
unsigned int write_flags,
struct cgroup_subsys_state *blkcg_css,
bool writeback)
{
struct btrfs_fs_info *fs_info = inode->root->fs_info;
struct bio *bio = NULL;
struct compressed_bio *cb;
u64 cur_disk_bytenr = disk_start;
u64 next_stripe_start;
blk_status_t ret;
int skip_sum = inode->flags & BTRFS_INODE_NODATASUM;
const bool use_append = btrfs_use_zone_append(inode, disk_start);
const unsigned int bio_op = use_append ? REQ_OP_ZONE_APPEND : REQ_OP_WRITE;
ASSERT(IS_ALIGNED(start, fs_info->sectorsize) &&
IS_ALIGNED(len, fs_info->sectorsize));
cb = kmalloc(compressed_bio_size(fs_info, compressed_len), GFP_NOFS);
if (!cb)
return BLK_STS_RESOURCE;
refcount_set(&cb->pending_sectors, compressed_len >> fs_info->sectorsize_bits);
cb->status = BLK_STS_OK;
cb->inode = &inode->vfs_inode;
cb->start = start;
cb->len = len;
cb->mirror_num = 0;
cb->compressed_pages = compressed_pages;
cb->compressed_len = compressed_len;
cb->writeback = writeback;
cb->orig_bio = NULL;
cb->nr_pages = nr_pages;
if (blkcg_css)
kthread_associate_blkcg(blkcg_css);
while (cur_disk_bytenr < disk_start + compressed_len) {
u64 offset = cur_disk_bytenr - disk_start;
unsigned int index = offset >> PAGE_SHIFT;
unsigned int real_size;
unsigned int added;
struct page *page = compressed_pages[index];
bool submit = false;
/* Allocate new bio if submitted or not yet allocated */
if (!bio) {
bio = alloc_compressed_bio(cb, cur_disk_bytenr,
bio_op | write_flags, end_compressed_bio_write,
&next_stripe_start);
if (IS_ERR(bio)) {
ret = errno_to_blk_status(PTR_ERR(bio));
bio = NULL;
goto finish_cb;
}
if (blkcg_css)
bio->bi_opf |= REQ_CGROUP_PUNT;
}
/*
* We should never reach next_stripe_start start as we will
* submit comp_bio when reach the boundary immediately.
*/
ASSERT(cur_disk_bytenr != next_stripe_start);
/*
* We have various limits on the real read size:
* - stripe boundary
* - page boundary
* - compressed length boundary
*/
real_size = min_t(u64, U32_MAX, next_stripe_start - cur_disk_bytenr);
real_size = min_t(u64, real_size, PAGE_SIZE - offset_in_page(offset));
real_size = min_t(u64, real_size, compressed_len - offset);
ASSERT(IS_ALIGNED(real_size, fs_info->sectorsize));
if (use_append)
added = bio_add_zone_append_page(bio, page, real_size,
offset_in_page(offset));
else
added = bio_add_page(bio, page, real_size,
offset_in_page(offset));
/* Reached zoned boundary */
if (added == 0)
submit = true;
cur_disk_bytenr += added;
/* Reached stripe boundary */
if (cur_disk_bytenr == next_stripe_start)
submit = true;
/* Finished the range */
if (cur_disk_bytenr == disk_start + compressed_len)
submit = true;
if (submit) {
if (!skip_sum) {
ret = btrfs_csum_one_bio(inode, bio, start, true);
if (ret)
goto finish_cb;
}
ret = submit_compressed_bio(fs_info, cb, bio, 0);
if (ret)
goto finish_cb;
bio = NULL;
}
cond_resched();
}
if (blkcg_css)
kthread_associate_blkcg(NULL);
return 0;
finish_cb:
if (blkcg_css)
kthread_associate_blkcg(NULL);
if (bio) {
bio->bi_status = ret;
bio_endio(bio);
}
/* Last byte of @cb is submitted, endio will free @cb */
if (cur_disk_bytenr == disk_start + compressed_len)
return ret;
wait_var_event(cb, refcount_read(&cb->pending_sectors) ==
(disk_start + compressed_len - cur_disk_bytenr) >>
fs_info->sectorsize_bits);
/*
* Even with previous bio ended, we should still have io not yet
* submitted, thus need to finish manually.
*/
ASSERT(refcount_read(&cb->pending_sectors));
/* Now we are the only one referring @cb, can finish it safely. */
finish_compressed_bio_write(cb);
return ret;
}
static u64 bio_end_offset(struct bio *bio)
{
struct bio_vec *last = bio_last_bvec_all(bio);
return page_offset(last->bv_page) + last->bv_len + last->bv_offset;
}
/*
* Add extra pages in the same compressed file extent so that we don't need to
* re-read the same extent again and again.
*
* NOTE: this won't work well for subpage, as for subpage read, we lock the
* full page then submit bio for each compressed/regular extents.
*
* This means, if we have several sectors in the same page points to the same
* on-disk compressed data, we will re-read the same extent many times and
* this function can only help for the next page.
*/
static noinline int add_ra_bio_pages(struct inode *inode,
u64 compressed_end,
struct compressed_bio *cb)
{
struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
unsigned long end_index;
u64 cur = bio_end_offset(cb->orig_bio);
u64 isize = i_size_read(inode);
int ret;
struct page *page;
struct extent_map *em;
struct address_space *mapping = inode->i_mapping;
struct extent_map_tree *em_tree;
struct extent_io_tree *tree;
int sectors_missed = 0;
em_tree = &BTRFS_I(inode)->extent_tree;
tree = &BTRFS_I(inode)->io_tree;
if (isize == 0)
return 0;
/*
* For current subpage support, we only support 64K page size,
* which means maximum compressed extent size (128K) is just 2x page
* size.
* This makes readahead less effective, so here disable readahead for
* subpage for now, until full compressed write is supported.
*/
if (btrfs_sb(inode->i_sb)->sectorsize < PAGE_SIZE)
return 0;
end_index = (i_size_read(inode) - 1) >> PAGE_SHIFT;
while (cur < compressed_end) {
u64 page_end;
u64 pg_index = cur >> PAGE_SHIFT;
u32 add_size;
if (pg_index > end_index)
break;
page = xa_load(&mapping->i_pages, pg_index);
if (page && !xa_is_value(page)) {
sectors_missed += (PAGE_SIZE - offset_in_page(cur)) >>
fs_info->sectorsize_bits;
/* Beyond threshold, no need to continue */
if (sectors_missed > 4)
break;
/*
* Jump to next page start as we already have page for
* current offset.
*/
cur = (pg_index << PAGE_SHIFT) + PAGE_SIZE;
continue;
}
page = __page_cache_alloc(mapping_gfp_constraint(mapping,
~__GFP_FS));
if (!page)
break;
if (add_to_page_cache_lru(page, mapping, pg_index, GFP_NOFS)) {
put_page(page);
/* There is already a page, skip to page end */
cur = (pg_index << PAGE_SHIFT) + PAGE_SIZE;
continue;
}
ret = set_page_extent_mapped(page);
if (ret < 0) {
unlock_page(page);
put_page(page);
break;
}
page_end = (pg_index << PAGE_SHIFT) + PAGE_SIZE - 1;
lock_extent(tree, cur, page_end);
read_lock(&em_tree->lock);
em = lookup_extent_mapping(em_tree, cur, page_end + 1 - cur);
read_unlock(&em_tree->lock);
/*
* At this point, we have a locked page in the page cache for
* these bytes in the file. But, we have to make sure they map
* to this compressed extent on disk.
*/
if (!em || cur < em->start ||
(cur + fs_info->sectorsize > extent_map_end(em)) ||
(em->block_start >> 9) != cb->orig_bio->bi_iter.bi_sector) {
free_extent_map(em);
unlock_extent(tree, cur, page_end);
unlock_page(page);
put_page(page);
break;
}
free_extent_map(em);
if (page->index == end_index) {
size_t zero_offset = offset_in_page(isize);
if (zero_offset) {
int zeros;
zeros = PAGE_SIZE - zero_offset;
memzero_page(page, zero_offset, zeros);
flush_dcache_page(page);
}
}
add_size = min(em->start + em->len, page_end + 1) - cur;
ret = bio_add_page(cb->orig_bio, page, add_size, offset_in_page(cur));
if (ret != add_size) {
unlock_extent(tree, cur, page_end);
unlock_page(page);
put_page(page);
break;
}
/*
* If it's subpage, we also need to increase its
* subpage::readers number, as at endio we will decrease
* subpage::readers and to unlock the page.
*/
if (fs_info->sectorsize < PAGE_SIZE)
btrfs_subpage_start_reader(fs_info, page, cur, add_size);
put_page(page);
cur += add_size;
}
return 0;
}
/*
* for a compressed read, the bio we get passed has all the inode pages
* in it. We don't actually do IO on those pages but allocate new ones
* to hold the compressed pages on disk.
*
* bio->bi_iter.bi_sector points to the compressed extent on disk
* bio->bi_io_vec points to all of the inode pages
*
* After the compressed pages are read, we copy the bytes into the
* bio we were passed and then call the bio end_io calls
*/
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 int compressed_len;
unsigned int nr_pages;
unsigned int pg_index;
struct bio *comp_bio = NULL;
const u64 disk_bytenr = bio->bi_iter.bi_sector << SECTOR_SHIFT;
u64 cur_disk_byte = disk_bytenr;
u64 next_stripe_start;
u64 file_offset;
u64 em_len;
u64 em_start;
struct extent_map *em;
blk_status_t ret;
int faili = 0;
u8 *sums;
em_tree = &BTRFS_I(inode)->extent_tree;
file_offset = bio_first_bvec_all(bio)->bv_offset +
page_offset(bio_first_page_all(bio));
/* we need the actual starting offset of this extent in the file */
read_lock(&em_tree->lock);
em = lookup_extent_mapping(em_tree, file_offset, fs_info->sectorsize);
read_unlock(&em_tree->lock);
if (!em) {
ret = BLK_STS_IOERR;
goto out;
}
ASSERT(em->compress_type != BTRFS_COMPRESS_NONE);
compressed_len = em->block_len;
cb = kmalloc(compressed_bio_size(fs_info, compressed_len), GFP_NOFS);
if (!cb) {
ret = BLK_STS_RESOURCE;
goto out;
}
refcount_set(&cb->pending_sectors, compressed_len >> fs_info->sectorsize_bits);
cb->status = BLK_STS_OK;
cb->inode = inode;
cb->mirror_num = mirror_num;
sums = cb->sums;
cb->start = em->orig_start;
em_len = em->len;
em_start = em->start;
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) {
ret = BLK_STS_RESOURCE;
goto fail1;
}
for (pg_index = 0; pg_index < nr_pages; pg_index++) {
cb->compressed_pages[pg_index] = alloc_page(GFP_NOFS);
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;
while (cur_disk_byte < disk_bytenr + compressed_len) {
u64 offset = cur_disk_byte - disk_bytenr;
unsigned int index = offset >> PAGE_SHIFT;
unsigned int real_size;
unsigned int added;
struct page *page = cb->compressed_pages[index];
bool submit = false;
/* Allocate new bio if submitted or not yet allocated */
if (!comp_bio) {
comp_bio = alloc_compressed_bio(cb, cur_disk_byte,
REQ_OP_READ, end_compressed_bio_read,
&next_stripe_start);
if (IS_ERR(comp_bio)) {
ret = errno_to_blk_status(PTR_ERR(comp_bio));
comp_bio = NULL;
goto finish_cb;
}
}
/*
* We should never reach next_stripe_start start as we will
* submit comp_bio when reach the boundary immediately.
*/
ASSERT(cur_disk_byte != next_stripe_start);
/*
* We have various limit on the real read size:
* - stripe boundary
* - page boundary
* - compressed length boundary
*/
real_size = min_t(u64, U32_MAX, next_stripe_start - cur_disk_byte);
real_size = min_t(u64, real_size, PAGE_SIZE - offset_in_page(offset));
real_size = min_t(u64, real_size, compressed_len - offset);
ASSERT(IS_ALIGNED(real_size, fs_info->sectorsize));
added = bio_add_page(comp_bio, page, real_size, offset_in_page(offset));
/*
* Maximum compressed extent is smaller than bio size limit,
* thus bio_add_page() should always success.
*/
ASSERT(added == real_size);
cur_disk_byte += added;
/* Reached stripe boundary, need to submit */
if (cur_disk_byte == next_stripe_start)
submit = true;
/* Has finished the range, need to submit */
if (cur_disk_byte == disk_bytenr + compressed_len)
submit = true;
if (submit) {
unsigned int nr_sectors;
ret = btrfs_lookup_bio_sums(inode, comp_bio, sums);
if (ret)
goto finish_cb;
nr_sectors = DIV_ROUND_UP(comp_bio->bi_iter.bi_size,
fs_info->sectorsize);
sums += fs_info->csum_size * nr_sectors;
ret = submit_compressed_bio(fs_info, cb, comp_bio, mirror_num);
if (ret)
goto finish_cb;
comp_bio = NULL;
}
}
return BLK_STS_OK;
fail2:
while (faili >= 0) {
__free_page(cb->compressed_pages[faili]);
faili--;
}
kfree(cb->compressed_pages);
fail1:
kfree(cb);
out:
free_extent_map(em);
bio->bi_status = ret;
bio_endio(bio);
return ret;
finish_cb:
if (comp_bio) {
comp_bio->bi_status = ret;
bio_endio(comp_bio);
}
/* All bytes of @cb is submitted, endio will free @cb */
if (cur_disk_byte == disk_bytenr + compressed_len)
return ret;
wait_var_event(cb, refcount_read(&cb->pending_sectors) ==
(disk_bytenr + compressed_len - cur_disk_byte) >>
fs_info->sectorsize_bits);
/*
* Even with previous bio ended, we should still have io not yet
* submitted, thus need to finish @cb manually.
*/
ASSERT(refcount_read(&cb->pending_sectors));
/* Now we are the only one referring @cb, can finish it safely. */
finish_compressed_bio_read(cb);
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
*/
int btrfs_compress_pages(unsigned int type_level, struct address_space *mapping,
u64 start, struct page **pages,
unsigned long *out_pages,
unsigned long *total_in,
unsigned long *total_out)
{
int type = btrfs_compress_type(type_level);
int level = btrfs_compress_level(type_level);
struct list_head *workspace;
int ret;
level = btrfs_compress_set_level(type, level);
workspace = get_workspace(type, level);
ret = compression_compress_pages(type, workspace, mapping, start, pages,
out_pages, total_in, total_out);
put_workspace(type, workspace);
return ret;
}
static int btrfs_decompress_bio(struct compressed_bio *cb)
{
struct list_head *workspace;
int ret;
int type = cb->compress_type;
workspace = get_workspace(type, 0);
ret = compression_decompress_bio(workspace, cb);
put_workspace(type, workspace);
return ret;
}
/*
* a less complex decompression routine. Our compressed data fits in a
* single page, and we want to read a single page out of it.
* start_byte tells us the offset into the compressed data we're interested in
*/
int btrfs_decompress(int type, unsigned char *data_in, struct page *dest_page,
unsigned long start_byte, size_t srclen, size_t destlen)
{
struct list_head *workspace;
int ret;
workspace = get_workspace(type, 0);
ret = compression_decompress(type, workspace, data_in, dest_page,
start_byte, srclen, destlen);
put_workspace(type, workspace);
return ret;
}
void __init btrfs_init_compress(void)
{
btrfs_init_workspace_manager(BTRFS_COMPRESS_NONE);
btrfs_init_workspace_manager(BTRFS_COMPRESS_ZLIB);
btrfs_init_workspace_manager(BTRFS_COMPRESS_LZO);
zstd_init_workspace_manager();
}
void __cold btrfs_exit_compress(void)
{
btrfs_cleanup_workspace_manager(BTRFS_COMPRESS_NONE);
btrfs_cleanup_workspace_manager(BTRFS_COMPRESS_ZLIB);
btrfs_cleanup_workspace_manager(BTRFS_COMPRESS_LZO);
zstd_cleanup_workspace_manager();
}
/*
* Copy decompressed data from working buffer to pages.
*
* @buf: The decompressed data buffer
* @buf_len: The decompressed data length
* @decompressed: Number of bytes that are already decompressed inside the
* compressed extent
* @cb: The compressed extent descriptor
* @orig_bio: The original bio that the caller wants to read for
*
* An easier to understand graph is like below:
*
* |<- orig_bio ->| |<- orig_bio->|
* |<------- full decompressed extent ----->|
* |<----------- @cb range ---->|
* | |<-- @buf_len -->|
* |<--- @decompressed --->|
*
* Note that, @cb can be a subpage of the full decompressed extent, but
* @cb->start always has the same as the orig_file_offset value of the full
* decompressed extent.
*
* When reading compressed extent, we have to read the full compressed extent,
* while @orig_bio may only want part of the range.
* Thus this function will ensure only data covered by @orig_bio will be copied
* to.
*
* Return 0 if we have copied all needed contents for @orig_bio.
* Return >0 if we need continue decompress.
*/
int btrfs_decompress_buf2page(const char *buf, u32 buf_len,
struct compressed_bio *cb, u32 decompressed)
{
struct bio *orig_bio = cb->orig_bio;
/* Offset inside the full decompressed extent */
u32 cur_offset;
cur_offset = decompressed;
/* The main loop to do the copy */
while (cur_offset < decompressed + buf_len) {
struct bio_vec bvec;
size_t copy_len;
u32 copy_start;
/* Offset inside the full decompressed extent */
u32 bvec_offset;
bvec = bio_iter_iovec(orig_bio, orig_bio->bi_iter);
/*
* cb->start may underflow, but subtracting that value can still
* give us correct offset inside the full decompressed extent.
*/
bvec_offset = page_offset(bvec.bv_page) + bvec.bv_offset - cb->start;
/* Haven't reached the bvec range, exit */
if (decompressed + buf_len <= bvec_offset)
return 1;
copy_start = max(cur_offset, bvec_offset);
copy_len = min(bvec_offset + bvec.bv_len,
decompressed + buf_len) - copy_start;
ASSERT(copy_len);
/*
* Extra range check to ensure we didn't go beyond
* @buf + @buf_len.
*/
ASSERT(copy_start - decompressed < buf_len);
memcpy_to_page(bvec.bv_page, bvec.bv_offset,
buf + copy_start - decompressed, copy_len);
flush_dcache_page(bvec.bv_page);
cur_offset += copy_len;
bio_advance(orig_bio, copy_len);
/* Finished the bio */
if (!orig_bio->bi_iter.bi_size)
return 0;
}
return 1;
}
/*
* Shannon Entropy calculation
*
* Pure byte distribution analysis fails to determine compressibility of data.
* Try calculating entropy to estimate the average minimum number of bits
* needed to encode the sampled data.
*
* For convenience, return the percentage of needed bits, instead of amount of
* bits directly.
*
* @ENTROPY_LVL_ACEPTABLE - below that threshold, sample has low byte entropy
* and can be compressible with high probability
*
* @ENTROPY_LVL_HIGH - data are not compressible with high probability
*
* Use of ilog2() decreases precision, we lower the LVL to 5 to compensate.
*/
#define ENTROPY_LVL_ACEPTABLE (65)
#define ENTROPY_LVL_HIGH (80)
/*
* For increasead precision in shannon_entropy calculation,
* let's do pow(n, M) to save more digits after comma:
*
* - maximum int bit length is 64
* - ilog2(MAX_SAMPLE_SIZE) -> 13
* - 13 * 4 = 52 < 64 -> M = 4
*
* So use pow(n, 4).
*/
static inline u32 ilog2_w(u64 n)
{
return ilog2(n * n * n * n);
}
static u32 shannon_entropy(struct heuristic_ws *ws)
{
const u32 entropy_max = 8 * ilog2_w(2);
u32 entropy_sum = 0;
u32 p, p_base, sz_base;
u32 i;
sz_base = ilog2_w(ws->sample_size);
for (i = 0; i < BUCKET_SIZE && ws->bucket[i].count > 0; i++) {
p = ws->bucket[i].count;
p_base = ilog2_w(p);
entropy_sum += p * (sz_base - p_base);
}
entropy_sum /= ws->sample_size;
return entropy_sum * 100 / entropy_max;
}
#define RADIX_BASE 4U
#define COUNTERS_SIZE (1U << RADIX_BASE)
static u8 get4bits(u64 num, int shift) {
u8 low4bits;
num >>= shift;
/* Reverse order */
low4bits = (COUNTERS_SIZE - 1) - (num % COUNTERS_SIZE);
return low4bits;
}
/*
* Use 4 bits as radix base
* Use 16 u32 counters for calculating new position in buf array
*
* @array - array that will be sorted
* @array_buf - buffer array to store sorting results
* must be equal in size to @array
* @num - array size
*/
static void radix_sort(struct bucket_item *array, struct bucket_item *array_buf,
int num)
{
u64 max_num;
u64 buf_num;
u32 counters[COUNTERS_SIZE];
u32 new_addr;
u32 addr;
int bitlen;
int shift;
int i;
/*
* Try avoid useless loop iterations for small numbers stored in big
* counters. Example: 48 33 4 ... in 64bit array
*/
max_num = array[0].count;
for (i = 1; i < num; i++) {
buf_num = array[i].count;
if (buf_num > max_num)
max_num = buf_num;
}
buf_num = ilog2(max_num);
bitlen = ALIGN(buf_num, RADIX_BASE * 2);
shift = 0;
while (shift < bitlen) {
memset(counters, 0, sizeof(counters));
for (i = 0; i < num; i++) {
buf_num = array[i].count;
addr = get4bits(buf_num, shift);
counters[addr]++;
}
for (i = 1; i < COUNTERS_SIZE; i++)
counters[i] += counters[i - 1];
for (i = num - 1; i >= 0; i--) {
buf_num = array[i].count;
addr = get4bits(buf_num, shift);
counters[addr]--;
new_addr = counters[addr];
array_buf[new_addr] = array[i];
}
shift += RADIX_BASE;
/*
* Normal radix expects to move data from a temporary array, to
* the main one. But that requires some CPU time. Avoid that
* by doing another sort iteration to original array instead of
* memcpy()
*/
memset(counters, 0, sizeof(counters));
for (i = 0; i < num; i ++) {
buf_num = array_buf[i].count;
addr = get4bits(buf_num, shift);
counters[addr]++;
}
for (i = 1; i < COUNTERS_SIZE; i++)
counters[i] += counters[i - 1];
for (i = num - 1; i >= 0; i--) {
buf_num = array_buf[i].count;
addr = get4bits(buf_num, shift);
counters[addr]--;
new_addr = counters[addr];
array[new_addr] = array_buf[i];
}
shift += RADIX_BASE;
}
}
/*
* Size of the core byte set - how many bytes cover 90% of the sample
*
* There are several types of structured binary data that use nearly all byte
* values. The distribution can be uniform and counts in all buckets will be
* nearly the same (eg. encrypted data). Unlikely to be compressible.
*
* Other possibility is normal (Gaussian) distribution, where the data could
* be potentially compressible, but we have to take a few more steps to decide
* how much.
*
* @BYTE_CORE_SET_LOW - main part of byte values repeated frequently,
* compression algo can easy fix that
* @BYTE_CORE_SET_HIGH - data have uniform distribution and with high
* probability is not compressible
*/
#define BYTE_CORE_SET_LOW (64)
#define BYTE_CORE_SET_HIGH (200)
static int byte_core_set_size(struct heuristic_ws *ws)
{
u32 i;
u32 coreset_sum = 0;
const u32 core_set_threshold = ws->sample_size * 90 / 100;
struct bucket_item *bucket = ws->bucket;
/* Sort in reverse order */
radix_sort(ws->bucket, ws->bucket_b, BUCKET_SIZE);
for (i = 0; i < BYTE_CORE_SET_LOW; i++)
coreset_sum += bucket[i].count;
if (coreset_sum > core_set_threshold)
return i;
for (; i < BYTE_CORE_SET_HIGH && bucket[i].count > 0; i++) {
coreset_sum += bucket[i].count;
if (coreset_sum > core_set_threshold)
break;
}
return i;
}
/*
* Count byte values in buckets.
* This heuristic can detect textual data (configs, xml, json, html, etc).
* Because in most text-like data byte set is restricted to limited number of
* possible characters, and that restriction in most cases makes data easy to
* compress.
*
* @BYTE_SET_THRESHOLD - consider all data within this byte set size:
* less - compressible
* more - need additional analysis
*/
#define BYTE_SET_THRESHOLD (64)
static u32 byte_set_size(const struct heuristic_ws *ws)
{
u32 i;
u32 byte_set_size = 0;
for (i = 0; i < BYTE_SET_THRESHOLD; i++) {
if (ws->bucket[i].count > 0)
byte_set_size++;
}
/*
* Continue collecting count of byte values in buckets. If the byte
* set size is bigger then the threshold, it's pointless to continue,
* the detection technique would fail for this type of data.
*/
for (; i < BUCKET_SIZE; i++) {
if (ws->bucket[i].count > 0) {
byte_set_size++;
if (byte_set_size > BYTE_SET_THRESHOLD)
return byte_set_size;
}
}
return byte_set_size;
}
static bool sample_repeated_patterns(struct heuristic_ws *ws)
{
const u32 half_of_sample = ws->sample_size / 2;
const u8 *data = ws->sample;
return memcmp(&data[0], &data[half_of_sample], half_of_sample) == 0;
}
static void heuristic_collect_sample(struct inode *inode, u64 start, u64 end,
struct heuristic_ws *ws)
{
struct page *page;
u64 index, index_end;
u32 i, curr_sample_pos;
u8 *in_data;
/*
* Compression handles the input data by chunks of 128KiB
* (defined by BTRFS_MAX_UNCOMPRESSED)
*
* We do the same for the heuristic and loop over the whole range.
*
* MAX_SAMPLE_SIZE - calculated under assumption that heuristic will
* process no more than BTRFS_MAX_UNCOMPRESSED at a time.
*/
if (end - start > BTRFS_MAX_UNCOMPRESSED)
end = start + BTRFS_MAX_UNCOMPRESSED;
index = start >> PAGE_SHIFT;
index_end = end >> PAGE_SHIFT;
/* Don't miss unaligned end */
if (!IS_ALIGNED(end, PAGE_SIZE))
index_end++;
curr_sample_pos = 0;
while (index < index_end) {
page = find_get_page(inode->i_mapping, index);
in_data = kmap_local_page(page);
/* Handle case where the start is not aligned to PAGE_SIZE */
i = start % PAGE_SIZE;
while (i < PAGE_SIZE - SAMPLING_READ_SIZE) {
/* Don't sample any garbage from the last page */
if (start > end - SAMPLING_READ_SIZE)
break;
memcpy(&ws->sample[curr_sample_pos], &in_data[i],
SAMPLING_READ_SIZE);
i += SAMPLING_INTERVAL;
start += SAMPLING_INTERVAL;
curr_sample_pos += SAMPLING_READ_SIZE;
}
kunmap_local(in_data);
put_page(page);
index++;
}
ws->sample_size = curr_sample_pos;
}
/*
* Compression heuristic.
*
* For now is's a naive and optimistic 'return true', we'll extend the logic to
* quickly (compared to direct compression) detect data characteristics
* (compressible/uncompressible) to avoid wasting CPU time on uncompressible
* data.
*
* The following types of analysis can be performed:
* - detect mostly zero data
* - detect data with low "byte set" size (text, etc)
* - detect data with low/high "core byte" set
*
* Return non-zero if the compression should be done, 0 otherwise.
*/
int btrfs_compress_heuristic(struct inode *inode, u64 start, u64 end)
{
struct list_head *ws_list = get_workspace(0, 0);
struct heuristic_ws *ws;
u32 i;
u8 byte;
int ret = 0;
ws = list_entry(ws_list, struct heuristic_ws, list);
heuristic_collect_sample(inode, start, end, ws);
if (sample_repeated_patterns(ws)) {
ret = 1;
goto out;
}
memset(ws->bucket, 0, sizeof(*ws->bucket)*BUCKET_SIZE);
for (i = 0; i < ws->sample_size; i++) {
byte = ws->sample[i];
ws->bucket[byte].count++;
}
i = byte_set_size(ws);
if (i < BYTE_SET_THRESHOLD) {
ret = 2;
goto out;
}
i = byte_core_set_size(ws);
if (i <= BYTE_CORE_SET_LOW) {
ret = 3;
goto out;
}
if (i >= BYTE_CORE_SET_HIGH) {
ret = 0;
goto out;
}
i = shannon_entropy(ws);
if (i <= ENTROPY_LVL_ACEPTABLE) {
ret = 4;
goto out;
}
/*
* For the levels below ENTROPY_LVL_HIGH, additional analysis would be
* needed to give green light to compression.
*
* For now just assume that compression at that level is not worth the
* resources because:
*
* 1. it is possible to defrag the data later
*
* 2. the data would turn out to be hardly compressible, eg. 150 byte
* values, every bucket has counter at level ~54. The heuristic would
* be confused. This can happen when data have some internal repeated
* patterns like "abbacbbc...". This can be detected by analyzing
* pairs of bytes, which is too costly.
*/
if (i < ENTROPY_LVL_HIGH) {
ret = 5;
goto out;
} else {
ret = 0;
goto out;
}
out:
put_workspace(0, ws_list);
return ret;
}
/*
* Convert the compression suffix (eg. after "zlib" starting with ":") to
* level, unrecognized string will set the default level
*/
unsigned int btrfs_compress_str2level(unsigned int type, const char *str)
{
unsigned int level = 0;
int ret;
if (!type)
return 0;
if (str[0] == ':') {
ret = kstrtouint(str + 1, 10, &level);
if (ret)
level = 0;
}
level = btrfs_compress_set_level(type, level);
return level;
}
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