summaryrefslogtreecommitdiffstats
path: root/fs/btrfs/compression.c
diff options
context:
space:
mode:
Diffstat (limited to '')
-rw-r--r--fs/btrfs/compression.c1747
1 files changed, 1747 insertions, 0 deletions
diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
new file mode 100644
index 000000000..e6635fe70
--- /dev/null
+++ b/fs/btrfs/compression.c
@@ -0,0 +1,1747 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2008 Oracle. All rights reserved.
+ */
+
+#include <linux/kernel.h>
+#include <linux/bio.h>
+#include <linux/file.h>
+#include <linux/fs.h>
+#include <linux/pagemap.h>
+#include <linux/pagevec.h>
+#include <linux/highmem.h>
+#include <linux/kthread.h>
+#include <linux/time.h>
+#include <linux/init.h>
+#include <linux/string.h>
+#include <linux/backing-dev.h>
+#include <linux/writeback.h>
+#include <linux/psi.h>
+#include <linux/slab.h>
+#include <linux/sched/mm.h>
+#include <linux/log2.h>
+#include <crypto/hash.h>
+#include "misc.h"
+#include "ctree.h"
+#include "disk-io.h"
+#include "transaction.h"
+#include "btrfs_inode.h"
+#include "volumes.h"
+#include "ordered-data.h"
+#include "compression.h"
+#include "extent_io.h"
+#include "extent_map.h"
+#include "subpage.h"
+#include "zoned.h"
+
+static const char* const btrfs_compress_types[] = { "", "zlib", "lzo", "zstd" };
+
+const char* btrfs_compress_type2str(enum btrfs_compression_type type)
+{
+ switch (type) {
+ case BTRFS_COMPRESS_ZLIB:
+ case BTRFS_COMPRESS_LZO:
+ case BTRFS_COMPRESS_ZSTD:
+ case BTRFS_COMPRESS_NONE:
+ return btrfs_compress_types[type];
+ default:
+ break;
+ }
+
+ return NULL;
+}
+
+bool btrfs_compress_is_valid_type(const char *str, size_t len)
+{
+ int i;
+
+ for (i = 1; i < ARRAY_SIZE(btrfs_compress_types); i++) {
+ size_t comp_len = strlen(btrfs_compress_types[i]);
+
+ if (len < comp_len)
+ continue;
+
+ if (!strncmp(btrfs_compress_types[i], str, comp_len))
+ return true;
+ }
+ return false;
+}
+
+static int compression_compress_pages(int type, struct list_head *ws,
+ struct address_space *mapping, u64 start, struct page **pages,
+ unsigned long *out_pages, unsigned long *total_in,
+ unsigned long *total_out)
+{
+ switch (type) {
+ case BTRFS_COMPRESS_ZLIB:
+ return zlib_compress_pages(ws, mapping, start, pages,
+ out_pages, total_in, total_out);
+ case BTRFS_COMPRESS_LZO:
+ return lzo_compress_pages(ws, mapping, start, pages,
+ out_pages, total_in, total_out);
+ case BTRFS_COMPRESS_ZSTD:
+ return zstd_compress_pages(ws, mapping, start, pages,
+ out_pages, total_in, total_out);
+ case BTRFS_COMPRESS_NONE:
+ default:
+ /*
+ * This can happen when compression races with remount setting
+ * it to 'no compress', while caller doesn't call
+ * inode_need_compress() to check if we really need to
+ * compress.
+ *
+ * Not a big deal, just need to inform caller that we
+ * haven't allocated any pages yet.
+ */
+ *out_pages = 0;
+ return -E2BIG;
+ }
+}
+
+static int compression_decompress_bio(struct list_head *ws,
+ struct compressed_bio *cb)
+{
+ switch (cb->compress_type) {
+ case BTRFS_COMPRESS_ZLIB: return zlib_decompress_bio(ws, cb);
+ case BTRFS_COMPRESS_LZO: return lzo_decompress_bio(ws, cb);
+ case BTRFS_COMPRESS_ZSTD: return zstd_decompress_bio(ws, cb);
+ case BTRFS_COMPRESS_NONE:
+ default:
+ /*
+ * This can't happen, the type is validated several times
+ * before we get here.
+ */
+ BUG();
+ }
+}
+
+static int compression_decompress(int type, struct list_head *ws,
+ unsigned char *data_in, struct page *dest_page,
+ unsigned long start_byte, size_t srclen, size_t destlen)
+{
+ switch (type) {
+ case BTRFS_COMPRESS_ZLIB: return zlib_decompress(ws, data_in, dest_page,
+ start_byte, srclen, destlen);
+ case BTRFS_COMPRESS_LZO: return lzo_decompress(ws, data_in, dest_page,
+ start_byte, srclen, destlen);
+ case BTRFS_COMPRESS_ZSTD: return zstd_decompress(ws, data_in, dest_page,
+ start_byte, srclen, destlen);
+ case BTRFS_COMPRESS_NONE:
+ default:
+ /*
+ * This can't happen, the type is validated several times
+ * before we get here.
+ */
+ BUG();
+ }
+}
+
+static int btrfs_decompress_bio(struct compressed_bio *cb);
+
+static void finish_compressed_bio_read(struct compressed_bio *cb)
+{
+ unsigned int index;
+ struct page *page;
+
+ if (cb->status == BLK_STS_OK)
+ cb->status = errno_to_blk_status(btrfs_decompress_bio(cb));
+
+ /* Release the compressed pages */
+ for (index = 0; index < cb->nr_pages; index++) {
+ page = cb->compressed_pages[index];
+ page->mapping = NULL;
+ put_page(page);
+ }
+
+ /* Do io completion on the original bio */
+ btrfs_bio_end_io(btrfs_bio(cb->orig_bio), cb->status);
+
+ /* Finally free the cb struct */
+ kfree(cb->compressed_pages);
+ kfree(cb);
+}
+
+/*
+ * Verify the checksums and kick off repair if needed on the uncompressed data
+ * before decompressing it into the original bio and freeing the uncompressed
+ * pages.
+ */
+static void end_compressed_bio_read(struct btrfs_bio *bbio)
+{
+ struct compressed_bio *cb = bbio->private;
+ struct inode *inode = cb->inode;
+ struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
+ struct btrfs_inode *bi = BTRFS_I(inode);
+ bool csum = !(bi->flags & BTRFS_INODE_NODATASUM) &&
+ !test_bit(BTRFS_FS_STATE_NO_CSUMS, &fs_info->fs_state);
+ blk_status_t status = bbio->bio.bi_status;
+ struct bvec_iter iter;
+ struct bio_vec bv;
+ u32 offset;
+
+ btrfs_bio_for_each_sector(fs_info, bv, bbio, iter, offset) {
+ u64 start = bbio->file_offset + offset;
+
+ if (!status &&
+ (!csum || !btrfs_check_data_csum(inode, bbio, offset,
+ bv.bv_page, bv.bv_offset))) {
+ btrfs_clean_io_failure(bi, start, bv.bv_page,
+ bv.bv_offset);
+ } else {
+ int ret;
+
+ refcount_inc(&cb->pending_ios);
+ ret = btrfs_repair_one_sector(inode, bbio, offset,
+ bv.bv_page, bv.bv_offset,
+ btrfs_submit_data_read_bio);
+ if (ret) {
+ refcount_dec(&cb->pending_ios);
+ status = errno_to_blk_status(ret);
+ }
+ }
+ }
+
+ if (status)
+ cb->status = status;
+
+ if (refcount_dec_and_test(&cb->pending_ios))
+ finish_compressed_bio_read(cb);
+ btrfs_bio_free_csum(bbio);
+ bio_put(&bbio->bio);
+}
+
+/*
+ * Clear the writeback bits on all of the file
+ * pages for a compressed write
+ */
+static noinline void end_compressed_writeback(struct inode *inode,
+ const struct compressed_bio *cb)
+{
+ struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
+ unsigned long index = cb->start >> PAGE_SHIFT;
+ unsigned long end_index = (cb->start + cb->len - 1) >> PAGE_SHIFT;
+ struct folio_batch fbatch;
+ const int errno = blk_status_to_errno(cb->status);
+ int i;
+ int ret;
+
+ if (errno)
+ mapping_set_error(inode->i_mapping, errno);
+
+ folio_batch_init(&fbatch);
+ while (index <= end_index) {
+ ret = filemap_get_folios(inode->i_mapping, &index, end_index,
+ &fbatch);
+
+ if (ret == 0)
+ return;
+
+ for (i = 0; i < ret; i++) {
+ struct folio *folio = fbatch.folios[i];
+
+ if (errno)
+ folio_set_error(folio);
+ btrfs_page_clamp_clear_writeback(fs_info, &folio->page,
+ cb->start, cb->len);
+ }
+ folio_batch_release(&fbatch);
+ }
+ /* the inode may be gone now */
+}
+
+static void finish_compressed_bio_write(struct compressed_bio *cb)
+{
+ struct inode *inode = cb->inode;
+ unsigned int index;
+
+ /*
+ * Ok, we're the last bio for this extent, step one is to call back
+ * into the FS and do all the end_io operations.
+ */
+ btrfs_writepage_endio_finish_ordered(BTRFS_I(inode), NULL,
+ cb->start, cb->start + cb->len - 1,
+ cb->status == BLK_STS_OK);
+
+ if (cb->writeback)
+ end_compressed_writeback(inode, cb);
+ /* Note, our inode could be gone now */
+
+ /*
+ * Release the compressed pages, these came from alloc_page and
+ * are not attached to the inode at all
+ */
+ for (index = 0; index < cb->nr_pages; index++) {
+ struct page *page = cb->compressed_pages[index];
+
+ page->mapping = NULL;
+ put_page(page);
+ }
+
+ /* Finally free the cb struct */
+ kfree(cb->compressed_pages);
+ kfree(cb);
+}
+
+static void btrfs_finish_compressed_write_work(struct work_struct *work)
+{
+ struct compressed_bio *cb =
+ container_of(work, struct compressed_bio, write_end_work);
+
+ finish_compressed_bio_write(cb);
+}
+
+/*
+ * Do the cleanup once all the compressed pages hit the disk. This will clear
+ * writeback on the file pages and free the compressed pages.
+ *
+ * This also calls the writeback end hooks for the file pages so that metadata
+ * and checksums can be updated in the file.
+ */
+static void end_compressed_bio_write(struct btrfs_bio *bbio)
+{
+ struct compressed_bio *cb = bbio->private;
+
+ if (bbio->bio.bi_status)
+ cb->status = bbio->bio.bi_status;
+
+ if (refcount_dec_and_test(&cb->pending_ios)) {
+ struct btrfs_fs_info *fs_info = btrfs_sb(cb->inode->i_sb);
+
+ btrfs_record_physical_zoned(cb->inode, cb->start, &bbio->bio);
+ queue_work(fs_info->compressed_write_workers, &cb->write_end_work);
+ }
+ bio_put(&bbio->bio);
+}
+
+/*
+ * Allocate a compressed_bio, which will be used to read/write on-disk
+ * (aka, compressed) * data.
+ *
+ * @cb: The compressed_bio structure, which records all the needed
+ * information to bind the compressed data to the uncompressed
+ * page cache.
+ * @disk_byten: The logical bytenr where the compressed data will be read
+ * from or written to.
+ * @endio_func: The endio function to call after the IO for compressed data
+ * is finished.
+ * @next_stripe_start: Return value of logical bytenr of where next stripe starts.
+ * Let the caller know to only fill the bio up to the stripe
+ * boundary.
+ */
+
+
+static struct bio *alloc_compressed_bio(struct compressed_bio *cb, u64 disk_bytenr,
+ blk_opf_t opf,
+ btrfs_bio_end_io_t endio_func,
+ u64 *next_stripe_start)
+{
+ struct btrfs_fs_info *fs_info = btrfs_sb(cb->inode->i_sb);
+ struct btrfs_io_geometry geom;
+ struct extent_map *em;
+ struct bio *bio;
+ int ret;
+
+ bio = btrfs_bio_alloc(BIO_MAX_VECS, opf, endio_func, cb);
+ bio->bi_iter.bi_sector = disk_bytenr >> SECTOR_SHIFT;
+
+ em = btrfs_get_chunk_map(fs_info, disk_bytenr, fs_info->sectorsize);
+ if (IS_ERR(em)) {
+ bio_put(bio);
+ return ERR_CAST(em);
+ }
+
+ if (bio_op(bio) == REQ_OP_ZONE_APPEND)
+ bio_set_dev(bio, em->map_lookup->stripes[0].dev->bdev);
+
+ ret = btrfs_get_io_geometry(fs_info, em, btrfs_op(bio), disk_bytenr, &geom);
+ free_extent_map(em);
+ if (ret < 0) {
+ bio_put(bio);
+ return ERR_PTR(ret);
+ }
+ *next_stripe_start = disk_bytenr + geom.len;
+ refcount_inc(&cb->pending_ios);
+ return bio;
+}
+
+/*
+ * worker function to build and submit bios for previously compressed pages.
+ * The corresponding pages in the inode should be marked for writeback
+ * and the compressed pages should have a reference on them for dropping
+ * when the IO is complete.
+ *
+ * This also checksums the file bytes and gets things ready for
+ * the end io hooks.
+ */
+blk_status_t btrfs_submit_compressed_write(struct btrfs_inode *inode, u64 start,
+ unsigned int len, u64 disk_start,
+ unsigned int compressed_len,
+ struct page **compressed_pages,
+ unsigned int nr_pages,
+ blk_opf_t write_flags,
+ struct cgroup_subsys_state *blkcg_css,
+ bool writeback)
+{
+ struct btrfs_fs_info *fs_info = inode->root->fs_info;
+ struct bio *bio = NULL;
+ struct compressed_bio *cb;
+ u64 cur_disk_bytenr = disk_start;
+ u64 next_stripe_start;
+ blk_status_t ret = BLK_STS_OK;
+ int skip_sum = inode->flags & BTRFS_INODE_NODATASUM;
+ const bool use_append = btrfs_use_zone_append(inode, disk_start);
+ const enum req_op bio_op = use_append ? REQ_OP_ZONE_APPEND : REQ_OP_WRITE;
+
+ ASSERT(IS_ALIGNED(start, fs_info->sectorsize) &&
+ IS_ALIGNED(len, fs_info->sectorsize));
+ cb = kmalloc(sizeof(struct compressed_bio), GFP_NOFS);
+ if (!cb)
+ return BLK_STS_RESOURCE;
+ refcount_set(&cb->pending_ios, 1);
+ cb->status = BLK_STS_OK;
+ cb->inode = &inode->vfs_inode;
+ cb->start = start;
+ cb->len = len;
+ cb->compressed_pages = compressed_pages;
+ cb->compressed_len = compressed_len;
+ cb->writeback = writeback;
+ INIT_WORK(&cb->write_end_work, btrfs_finish_compressed_write_work);
+ cb->nr_pages = nr_pages;
+
+ if (blkcg_css)
+ kthread_associate_blkcg(blkcg_css);
+
+ while (cur_disk_bytenr < disk_start + compressed_len) {
+ u64 offset = cur_disk_bytenr - disk_start;
+ unsigned int index = offset >> PAGE_SHIFT;
+ unsigned int real_size;
+ unsigned int added;
+ struct page *page = compressed_pages[index];
+ bool submit = false;
+
+ /* Allocate new bio if submitted or not yet allocated */
+ if (!bio) {
+ bio = alloc_compressed_bio(cb, cur_disk_bytenr,
+ bio_op | write_flags, end_compressed_bio_write,
+ &next_stripe_start);
+ if (IS_ERR(bio)) {
+ ret = errno_to_blk_status(PTR_ERR(bio));
+ break;
+ }
+ if (blkcg_css)
+ bio->bi_opf |= REQ_CGROUP_PUNT;
+ }
+ /*
+ * We should never reach next_stripe_start start as we will
+ * submit comp_bio when reach the boundary immediately.
+ */
+ ASSERT(cur_disk_bytenr != next_stripe_start);
+
+ /*
+ * We have various limits on the real read size:
+ * - stripe boundary
+ * - page boundary
+ * - compressed length boundary
+ */
+ real_size = min_t(u64, U32_MAX, next_stripe_start - cur_disk_bytenr);
+ real_size = min_t(u64, real_size, PAGE_SIZE - offset_in_page(offset));
+ real_size = min_t(u64, real_size, compressed_len - offset);
+ ASSERT(IS_ALIGNED(real_size, fs_info->sectorsize));
+
+ if (use_append)
+ added = bio_add_zone_append_page(bio, page, real_size,
+ offset_in_page(offset));
+ else
+ added = bio_add_page(bio, page, real_size,
+ offset_in_page(offset));
+ /* Reached zoned boundary */
+ if (added == 0)
+ submit = true;
+
+ cur_disk_bytenr += added;
+ /* Reached stripe boundary */
+ if (cur_disk_bytenr == next_stripe_start)
+ submit = true;
+
+ /* Finished the range */
+ if (cur_disk_bytenr == disk_start + compressed_len)
+ submit = true;
+
+ if (submit) {
+ if (!skip_sum) {
+ ret = btrfs_csum_one_bio(inode, bio, start, true);
+ if (ret) {
+ btrfs_bio_end_io(btrfs_bio(bio), ret);
+ break;
+ }
+ }
+
+ ASSERT(bio->bi_iter.bi_size);
+ btrfs_submit_bio(fs_info, bio, 0);
+ bio = NULL;
+ }
+ cond_resched();
+ }
+
+ if (blkcg_css)
+ kthread_associate_blkcg(NULL);
+
+ if (refcount_dec_and_test(&cb->pending_ios))
+ finish_compressed_bio_write(cb);
+ return ret;
+}
+
+static u64 bio_end_offset(struct bio *bio)
+{
+ struct bio_vec *last = bio_last_bvec_all(bio);
+
+ return page_offset(last->bv_page) + last->bv_len + last->bv_offset;
+}
+
+/*
+ * Add extra pages in the same compressed file extent so that we don't need to
+ * re-read the same extent again and again.
+ *
+ * NOTE: this won't work well for subpage, as for subpage read, we lock the
+ * full page then submit bio for each compressed/regular extents.
+ *
+ * This means, if we have several sectors in the same page points to the same
+ * on-disk compressed data, we will re-read the same extent many times and
+ * this function can only help for the next page.
+ */
+static noinline int add_ra_bio_pages(struct inode *inode,
+ u64 compressed_end,
+ struct compressed_bio *cb,
+ int *memstall, unsigned long *pflags)
+{
+ struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
+ unsigned long end_index;
+ u64 cur = bio_end_offset(cb->orig_bio);
+ u64 isize = i_size_read(inode);
+ int ret;
+ struct page *page;
+ struct extent_map *em;
+ struct address_space *mapping = inode->i_mapping;
+ struct extent_map_tree *em_tree;
+ struct extent_io_tree *tree;
+ int sectors_missed = 0;
+
+ em_tree = &BTRFS_I(inode)->extent_tree;
+ tree = &BTRFS_I(inode)->io_tree;
+
+ if (isize == 0)
+ return 0;
+
+ /*
+ * For current subpage support, we only support 64K page size,
+ * which means maximum compressed extent size (128K) is just 2x page
+ * size.
+ * This makes readahead less effective, so here disable readahead for
+ * subpage for now, until full compressed write is supported.
+ */
+ if (btrfs_sb(inode->i_sb)->sectorsize < PAGE_SIZE)
+ return 0;
+
+ end_index = (i_size_read(inode) - 1) >> PAGE_SHIFT;
+
+ while (cur < compressed_end) {
+ u64 page_end;
+ u64 pg_index = cur >> PAGE_SHIFT;
+ u32 add_size;
+
+ if (pg_index > end_index)
+ break;
+
+ page = xa_load(&mapping->i_pages, pg_index);
+ if (page && !xa_is_value(page)) {
+ sectors_missed += (PAGE_SIZE - offset_in_page(cur)) >>
+ fs_info->sectorsize_bits;
+
+ /* Beyond threshold, no need to continue */
+ if (sectors_missed > 4)
+ break;
+
+ /*
+ * Jump to next page start as we already have page for
+ * current offset.
+ */
+ cur = (pg_index << PAGE_SHIFT) + PAGE_SIZE;
+ continue;
+ }
+
+ page = __page_cache_alloc(mapping_gfp_constraint(mapping,
+ ~__GFP_FS));
+ if (!page)
+ break;
+
+ if (add_to_page_cache_lru(page, mapping, pg_index, GFP_NOFS)) {
+ put_page(page);
+ /* There is already a page, skip to page end */
+ cur = (pg_index << PAGE_SHIFT) + PAGE_SIZE;
+ continue;
+ }
+
+ if (!*memstall && PageWorkingset(page)) {
+ psi_memstall_enter(pflags);
+ *memstall = 1;
+ }
+
+ ret = set_page_extent_mapped(page);
+ if (ret < 0) {
+ unlock_page(page);
+ put_page(page);
+ break;
+ }
+
+ page_end = (pg_index << PAGE_SHIFT) + PAGE_SIZE - 1;
+ lock_extent(tree, cur, page_end, NULL);
+ read_lock(&em_tree->lock);
+ em = lookup_extent_mapping(em_tree, cur, page_end + 1 - cur);
+ read_unlock(&em_tree->lock);
+
+ /*
+ * At this point, we have a locked page in the page cache for
+ * these bytes in the file. But, we have to make sure they map
+ * to this compressed extent on disk.
+ */
+ if (!em || cur < em->start ||
+ (cur + fs_info->sectorsize > extent_map_end(em)) ||
+ (em->block_start >> 9) != cb->orig_bio->bi_iter.bi_sector) {
+ free_extent_map(em);
+ unlock_extent(tree, cur, page_end, NULL);
+ unlock_page(page);
+ put_page(page);
+ break;
+ }
+ free_extent_map(em);
+
+ if (page->index == end_index) {
+ size_t zero_offset = offset_in_page(isize);
+
+ if (zero_offset) {
+ int zeros;
+ zeros = PAGE_SIZE - zero_offset;
+ memzero_page(page, zero_offset, zeros);
+ }
+ }
+
+ add_size = min(em->start + em->len, page_end + 1) - cur;
+ ret = bio_add_page(cb->orig_bio, page, add_size, offset_in_page(cur));
+ if (ret != add_size) {
+ unlock_extent(tree, cur, page_end, NULL);
+ unlock_page(page);
+ put_page(page);
+ break;
+ }
+ /*
+ * If it's subpage, we also need to increase its
+ * subpage::readers number, as at endio we will decrease
+ * subpage::readers and to unlock the page.
+ */
+ if (fs_info->sectorsize < PAGE_SIZE)
+ btrfs_subpage_start_reader(fs_info, page, cur, add_size);
+ put_page(page);
+ cur += add_size;
+ }
+ return 0;
+}
+
+/*
+ * for a compressed read, the bio we get passed has all the inode pages
+ * in it. We don't actually do IO on those pages but allocate new ones
+ * to hold the compressed pages on disk.
+ *
+ * bio->bi_iter.bi_sector points to the compressed extent on disk
+ * bio->bi_io_vec points to all of the inode pages
+ *
+ * After the compressed pages are read, we copy the bytes into the
+ * bio we were passed and then call the bio end_io calls
+ */
+void btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
+ int mirror_num)
+{
+ struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
+ struct extent_map_tree *em_tree;
+ struct compressed_bio *cb;
+ unsigned int compressed_len;
+ struct bio *comp_bio = NULL;
+ const u64 disk_bytenr = bio->bi_iter.bi_sector << SECTOR_SHIFT;
+ u64 cur_disk_byte = disk_bytenr;
+ u64 next_stripe_start;
+ u64 file_offset;
+ u64 em_len;
+ u64 em_start;
+ struct extent_map *em;
+ unsigned long pflags;
+ int memstall = 0;
+ blk_status_t ret;
+ int ret2;
+ int i;
+
+ em_tree = &BTRFS_I(inode)->extent_tree;
+
+ file_offset = bio_first_bvec_all(bio)->bv_offset +
+ page_offset(bio_first_page_all(bio));
+
+ /* we need the actual starting offset of this extent in the file */
+ read_lock(&em_tree->lock);
+ em = lookup_extent_mapping(em_tree, file_offset, fs_info->sectorsize);
+ read_unlock(&em_tree->lock);
+ if (!em) {
+ ret = BLK_STS_IOERR;
+ goto out;
+ }
+
+ ASSERT(em->compress_type != BTRFS_COMPRESS_NONE);
+ compressed_len = em->block_len;
+ cb = kmalloc(sizeof(struct compressed_bio), GFP_NOFS);
+ if (!cb) {
+ ret = BLK_STS_RESOURCE;
+ goto out;
+ }
+
+ refcount_set(&cb->pending_ios, 1);
+ cb->status = BLK_STS_OK;
+ cb->inode = inode;
+
+ cb->start = em->orig_start;
+ em_len = em->len;
+ em_start = em->start;
+
+ cb->len = bio->bi_iter.bi_size;
+ cb->compressed_len = compressed_len;
+ cb->compress_type = em->compress_type;
+ cb->orig_bio = bio;
+
+ free_extent_map(em);
+ em = NULL;
+
+ cb->nr_pages = DIV_ROUND_UP(compressed_len, PAGE_SIZE);
+ cb->compressed_pages = kcalloc(cb->nr_pages, sizeof(struct page *), GFP_NOFS);
+ if (!cb->compressed_pages) {
+ ret = BLK_STS_RESOURCE;
+ goto fail;
+ }
+
+ ret2 = btrfs_alloc_page_array(cb->nr_pages, cb->compressed_pages);
+ if (ret2) {
+ ret = BLK_STS_RESOURCE;
+ goto fail;
+ }
+
+ add_ra_bio_pages(inode, em_start + em_len, cb, &memstall, &pflags);
+
+ /* include any pages we added in add_ra-bio_pages */
+ cb->len = bio->bi_iter.bi_size;
+
+ while (cur_disk_byte < disk_bytenr + compressed_len) {
+ u64 offset = cur_disk_byte - disk_bytenr;
+ unsigned int index = offset >> PAGE_SHIFT;
+ unsigned int real_size;
+ unsigned int added;
+ struct page *page = cb->compressed_pages[index];
+ bool submit = false;
+
+ /* Allocate new bio if submitted or not yet allocated */
+ if (!comp_bio) {
+ comp_bio = alloc_compressed_bio(cb, cur_disk_byte,
+ REQ_OP_READ, end_compressed_bio_read,
+ &next_stripe_start);
+ if (IS_ERR(comp_bio)) {
+ cb->status = errno_to_blk_status(PTR_ERR(comp_bio));
+ break;
+ }
+ }
+ /*
+ * We should never reach next_stripe_start start as we will
+ * submit comp_bio when reach the boundary immediately.
+ */
+ ASSERT(cur_disk_byte != next_stripe_start);
+ /*
+ * We have various limit on the real read size:
+ * - stripe boundary
+ * - page boundary
+ * - compressed length boundary
+ */
+ real_size = min_t(u64, U32_MAX, next_stripe_start - cur_disk_byte);
+ real_size = min_t(u64, real_size, PAGE_SIZE - offset_in_page(offset));
+ real_size = min_t(u64, real_size, compressed_len - offset);
+ ASSERT(IS_ALIGNED(real_size, fs_info->sectorsize));
+
+ added = bio_add_page(comp_bio, page, real_size, offset_in_page(offset));
+ /*
+ * Maximum compressed extent is smaller than bio size limit,
+ * thus bio_add_page() should always success.
+ */
+ ASSERT(added == real_size);
+ cur_disk_byte += added;
+
+ /* Reached stripe boundary, need to submit */
+ if (cur_disk_byte == next_stripe_start)
+ submit = true;
+
+ /* Has finished the range, need to submit */
+ if (cur_disk_byte == disk_bytenr + compressed_len)
+ submit = true;
+
+ if (submit) {
+ /* Save the original iter for read repair */
+ if (bio_op(comp_bio) == REQ_OP_READ)
+ btrfs_bio(comp_bio)->iter = comp_bio->bi_iter;
+
+ /*
+ * Save the initial offset of this chunk, as there
+ * is no direct correlation between compressed pages and
+ * the original file offset. The field is only used for
+ * priting error messages.
+ */
+ btrfs_bio(comp_bio)->file_offset = file_offset;
+
+ ret = btrfs_lookup_bio_sums(inode, comp_bio, NULL);
+ if (ret) {
+ btrfs_bio_end_io(btrfs_bio(comp_bio), ret);
+ break;
+ }
+
+ ASSERT(comp_bio->bi_iter.bi_size);
+ btrfs_submit_bio(fs_info, comp_bio, mirror_num);
+ comp_bio = NULL;
+ }
+ }
+
+ if (memstall)
+ psi_memstall_leave(&pflags);
+
+ if (refcount_dec_and_test(&cb->pending_ios))
+ finish_compressed_bio_read(cb);
+ return;
+
+fail:
+ if (cb->compressed_pages) {
+ for (i = 0; i < cb->nr_pages; i++) {
+ if (cb->compressed_pages[i])
+ __free_page(cb->compressed_pages[i]);
+ }
+ }
+
+ kfree(cb->compressed_pages);
+ kfree(cb);
+out:
+ free_extent_map(em);
+ btrfs_bio_end_io(btrfs_bio(bio), ret);
+ return;
+}
+
+/*
+ * Heuristic uses systematic sampling to collect data from the input data
+ * range, the logic can be tuned by the following constants:
+ *
+ * @SAMPLING_READ_SIZE - how many bytes will be copied from for each sample
+ * @SAMPLING_INTERVAL - range from which the sampled data can be collected
+ */
+#define SAMPLING_READ_SIZE (16)
+#define SAMPLING_INTERVAL (256)
+
+/*
+ * For statistical analysis of the input data we consider bytes that form a
+ * Galois Field of 256 objects. Each object has an attribute count, ie. how
+ * many times the object appeared in the sample.
+ */
+#define BUCKET_SIZE (256)
+
+/*
+ * The size of the sample is based on a statistical sampling rule of thumb.
+ * The common way is to perform sampling tests as long as the number of
+ * elements in each cell is at least 5.
+ *
+ * Instead of 5, we choose 32 to obtain more accurate results.
+ * If the data contain the maximum number of symbols, which is 256, we obtain a
+ * sample size bound by 8192.
+ *
+ * For a sample of at most 8KB of data per data range: 16 consecutive bytes
+ * from up to 512 locations.
+ */
+#define MAX_SAMPLE_SIZE (BTRFS_MAX_UNCOMPRESSED * \
+ SAMPLING_READ_SIZE / SAMPLING_INTERVAL)
+
+struct bucket_item {
+ u32 count;
+};
+
+struct heuristic_ws {
+ /* Partial copy of input data */
+ u8 *sample;
+ u32 sample_size;
+ /* Buckets store counters for each byte value */
+ struct bucket_item *bucket;
+ /* Sorting buffer */
+ struct bucket_item *bucket_b;
+ struct list_head list;
+};
+
+static struct workspace_manager heuristic_wsm;
+
+static void free_heuristic_ws(struct list_head *ws)
+{
+ struct heuristic_ws *workspace;
+
+ workspace = list_entry(ws, struct heuristic_ws, list);
+
+ kvfree(workspace->sample);
+ kfree(workspace->bucket);
+ kfree(workspace->bucket_b);
+ kfree(workspace);
+}
+
+static struct list_head *alloc_heuristic_ws(unsigned int level)
+{
+ struct heuristic_ws *ws;
+
+ ws = kzalloc(sizeof(*ws), GFP_KERNEL);
+ if (!ws)
+ return ERR_PTR(-ENOMEM);
+
+ ws->sample = kvmalloc(MAX_SAMPLE_SIZE, GFP_KERNEL);
+ if (!ws->sample)
+ goto fail;
+
+ ws->bucket = kcalloc(BUCKET_SIZE, sizeof(*ws->bucket), GFP_KERNEL);
+ if (!ws->bucket)
+ goto fail;
+
+ ws->bucket_b = kcalloc(BUCKET_SIZE, sizeof(*ws->bucket_b), GFP_KERNEL);
+ if (!ws->bucket_b)
+ goto fail;
+
+ INIT_LIST_HEAD(&ws->list);
+ return &ws->list;
+fail:
+ free_heuristic_ws(&ws->list);
+ return ERR_PTR(-ENOMEM);
+}
+
+const struct btrfs_compress_op btrfs_heuristic_compress = {
+ .workspace_manager = &heuristic_wsm,
+};
+
+static const struct btrfs_compress_op * const btrfs_compress_op[] = {
+ /* The heuristic is represented as compression type 0 */
+ &btrfs_heuristic_compress,
+ &btrfs_zlib_compress,
+ &btrfs_lzo_compress,
+ &btrfs_zstd_compress,
+};
+
+static struct list_head *alloc_workspace(int type, unsigned int level)
+{
+ switch (type) {
+ case BTRFS_COMPRESS_NONE: return alloc_heuristic_ws(level);
+ case BTRFS_COMPRESS_ZLIB: return zlib_alloc_workspace(level);
+ case BTRFS_COMPRESS_LZO: return lzo_alloc_workspace(level);
+ case BTRFS_COMPRESS_ZSTD: return zstd_alloc_workspace(level);
+ default:
+ /*
+ * This can't happen, the type is validated several times
+ * before we get here.
+ */
+ BUG();
+ }
+}
+
+static void free_workspace(int type, struct list_head *ws)
+{
+ switch (type) {
+ case BTRFS_COMPRESS_NONE: return free_heuristic_ws(ws);
+ case BTRFS_COMPRESS_ZLIB: return zlib_free_workspace(ws);
+ case BTRFS_COMPRESS_LZO: return lzo_free_workspace(ws);
+ case BTRFS_COMPRESS_ZSTD: return zstd_free_workspace(ws);
+ default:
+ /*
+ * This can't happen, the type is validated several times
+ * before we get here.
+ */
+ BUG();
+ }
+}
+
+static void btrfs_init_workspace_manager(int type)
+{
+ struct workspace_manager *wsm;
+ struct list_head *workspace;
+
+ wsm = btrfs_compress_op[type]->workspace_manager;
+ INIT_LIST_HEAD(&wsm->idle_ws);
+ spin_lock_init(&wsm->ws_lock);
+ atomic_set(&wsm->total_ws, 0);
+ init_waitqueue_head(&wsm->ws_wait);
+
+ /*
+ * Preallocate one workspace for each compression type so we can
+ * guarantee forward progress in the worst case
+ */
+ workspace = alloc_workspace(type, 0);
+ if (IS_ERR(workspace)) {
+ pr_warn(
+ "BTRFS: cannot preallocate compression workspace, will try later\n");
+ } else {
+ atomic_set(&wsm->total_ws, 1);
+ wsm->free_ws = 1;
+ list_add(workspace, &wsm->idle_ws);
+ }
+}
+
+static void btrfs_cleanup_workspace_manager(int type)
+{
+ struct workspace_manager *wsman;
+ struct list_head *ws;
+
+ wsman = btrfs_compress_op[type]->workspace_manager;
+ while (!list_empty(&wsman->idle_ws)) {
+ ws = wsman->idle_ws.next;
+ list_del(ws);
+ free_workspace(type, ws);
+ atomic_dec(&wsman->total_ws);
+ }
+}
+
+/*
+ * This finds an available workspace or allocates a new one.
+ * If it's not possible to allocate a new one, waits until there's one.
+ * Preallocation makes a forward progress guarantees and we do not return
+ * errors.
+ */
+struct list_head *btrfs_get_workspace(int type, unsigned int level)
+{
+ struct workspace_manager *wsm;
+ struct list_head *workspace;
+ int cpus = num_online_cpus();
+ unsigned nofs_flag;
+ struct list_head *idle_ws;
+ spinlock_t *ws_lock;
+ atomic_t *total_ws;
+ wait_queue_head_t *ws_wait;
+ int *free_ws;
+
+ wsm = btrfs_compress_op[type]->workspace_manager;
+ idle_ws = &wsm->idle_ws;
+ ws_lock = &wsm->ws_lock;
+ total_ws = &wsm->total_ws;
+ ws_wait = &wsm->ws_wait;
+ free_ws = &wsm->free_ws;
+
+again:
+ spin_lock(ws_lock);
+ if (!list_empty(idle_ws)) {
+ workspace = idle_ws->next;
+ list_del(workspace);
+ (*free_ws)--;
+ spin_unlock(ws_lock);
+ return workspace;
+
+ }
+ if (atomic_read(total_ws) > cpus) {
+ DEFINE_WAIT(wait);
+
+ spin_unlock(ws_lock);
+ prepare_to_wait(ws_wait, &wait, TASK_UNINTERRUPTIBLE);
+ if (atomic_read(total_ws) > cpus && !*free_ws)
+ schedule();
+ finish_wait(ws_wait, &wait);
+ goto again;
+ }
+ atomic_inc(total_ws);
+ spin_unlock(ws_lock);
+
+ /*
+ * Allocation helpers call vmalloc that can't use GFP_NOFS, so we have
+ * to turn it off here because we might get called from the restricted
+ * context of btrfs_compress_bio/btrfs_compress_pages
+ */
+ nofs_flag = memalloc_nofs_save();
+ workspace = alloc_workspace(type, level);
+ memalloc_nofs_restore(nofs_flag);
+
+ if (IS_ERR(workspace)) {
+ atomic_dec(total_ws);
+ wake_up(ws_wait);
+
+ /*
+ * Do not return the error but go back to waiting. There's a
+ * workspace preallocated for each type and the compression
+ * time is bounded so we get to a workspace eventually. This
+ * makes our caller's life easier.
+ *
+ * To prevent silent and low-probability deadlocks (when the
+ * initial preallocation fails), check if there are any
+ * workspaces at all.
+ */
+ if (atomic_read(total_ws) == 0) {
+ static DEFINE_RATELIMIT_STATE(_rs,
+ /* once per minute */ 60 * HZ,
+ /* no burst */ 1);
+
+ if (__ratelimit(&_rs)) {
+ pr_warn("BTRFS: no compression workspaces, low memory, retrying\n");
+ }
+ }
+ goto again;
+ }
+ return workspace;
+}
+
+static struct list_head *get_workspace(int type, int level)
+{
+ switch (type) {
+ case BTRFS_COMPRESS_NONE: return btrfs_get_workspace(type, level);
+ case BTRFS_COMPRESS_ZLIB: return zlib_get_workspace(level);
+ case BTRFS_COMPRESS_LZO: return btrfs_get_workspace(type, level);
+ case BTRFS_COMPRESS_ZSTD: return zstd_get_workspace(level);
+ default:
+ /*
+ * This can't happen, the type is validated several times
+ * before we get here.
+ */
+ BUG();
+ }
+}
+
+/*
+ * put a workspace struct back on the list or free it if we have enough
+ * idle ones sitting around
+ */
+void btrfs_put_workspace(int type, struct list_head *ws)
+{
+ struct workspace_manager *wsm;
+ struct list_head *idle_ws;
+ spinlock_t *ws_lock;
+ atomic_t *total_ws;
+ wait_queue_head_t *ws_wait;
+ int *free_ws;
+
+ wsm = btrfs_compress_op[type]->workspace_manager;
+ idle_ws = &wsm->idle_ws;
+ ws_lock = &wsm->ws_lock;
+ total_ws = &wsm->total_ws;
+ ws_wait = &wsm->ws_wait;
+ free_ws = &wsm->free_ws;
+
+ spin_lock(ws_lock);
+ if (*free_ws <= num_online_cpus()) {
+ list_add(ws, idle_ws);
+ (*free_ws)++;
+ spin_unlock(ws_lock);
+ goto wake;
+ }
+ spin_unlock(ws_lock);
+
+ free_workspace(type, ws);
+ atomic_dec(total_ws);
+wake:
+ cond_wake_up(ws_wait);
+}
+
+static void put_workspace(int type, struct list_head *ws)
+{
+ switch (type) {
+ case BTRFS_COMPRESS_NONE: return btrfs_put_workspace(type, ws);
+ case BTRFS_COMPRESS_ZLIB: return btrfs_put_workspace(type, ws);
+ case BTRFS_COMPRESS_LZO: return btrfs_put_workspace(type, ws);
+ case BTRFS_COMPRESS_ZSTD: return zstd_put_workspace(ws);
+ default:
+ /*
+ * This can't happen, the type is validated several times
+ * before we get here.
+ */
+ BUG();
+ }
+}
+
+/*
+ * Adjust @level according to the limits of the compression algorithm or
+ * fallback to default
+ */
+static unsigned int btrfs_compress_set_level(int type, unsigned level)
+{
+ const struct btrfs_compress_op *ops = btrfs_compress_op[type];
+
+ if (level == 0)
+ level = ops->default_level;
+ else
+ level = min(level, ops->max_level);
+
+ return level;
+}
+
+/*
+ * Given an address space and start and length, compress the bytes into @pages
+ * that are allocated on demand.
+ *
+ * @type_level is encoded algorithm and level, where level 0 means whatever
+ * default the algorithm chooses and is opaque here;
+ * - compression algo are 0-3
+ * - the level are bits 4-7
+ *
+ * @out_pages is an in/out parameter, holds maximum number of pages to allocate
+ * and returns number of actually allocated pages
+ *
+ * @total_in is used to return the number of bytes actually read. It
+ * may be smaller than the input length if we had to exit early because we
+ * ran out of room in the pages array or because we cross the
+ * max_out threshold.
+ *
+ * @total_out is an in/out parameter, must be set to the input length and will
+ * be also used to return the total number of compressed bytes
+ */
+int btrfs_compress_pages(unsigned int type_level, struct address_space *mapping,
+ u64 start, struct page **pages,
+ unsigned long *out_pages,
+ unsigned long *total_in,
+ unsigned long *total_out)
+{
+ int type = btrfs_compress_type(type_level);
+ int level = btrfs_compress_level(type_level);
+ struct list_head *workspace;
+ int ret;
+
+ level = btrfs_compress_set_level(type, level);
+ workspace = get_workspace(type, level);
+ ret = compression_compress_pages(type, workspace, mapping, start, pages,
+ out_pages, total_in, total_out);
+ put_workspace(type, workspace);
+ return ret;
+}
+
+static int btrfs_decompress_bio(struct compressed_bio *cb)
+{
+ struct list_head *workspace;
+ int ret;
+ int type = cb->compress_type;
+
+ workspace = get_workspace(type, 0);
+ ret = compression_decompress_bio(workspace, cb);
+ put_workspace(type, workspace);
+
+ return ret;
+}
+
+/*
+ * a less complex decompression routine. Our compressed data fits in a
+ * single page, and we want to read a single page out of it.
+ * start_byte tells us the offset into the compressed data we're interested in
+ */
+int btrfs_decompress(int type, unsigned char *data_in, struct page *dest_page,
+ unsigned long start_byte, size_t srclen, size_t destlen)
+{
+ struct list_head *workspace;
+ int ret;
+
+ workspace = get_workspace(type, 0);
+ ret = compression_decompress(type, workspace, data_in, dest_page,
+ start_byte, srclen, destlen);
+ put_workspace(type, workspace);
+
+ return ret;
+}
+
+void __init btrfs_init_compress(void)
+{
+ btrfs_init_workspace_manager(BTRFS_COMPRESS_NONE);
+ btrfs_init_workspace_manager(BTRFS_COMPRESS_ZLIB);
+ btrfs_init_workspace_manager(BTRFS_COMPRESS_LZO);
+ zstd_init_workspace_manager();
+}
+
+void __cold btrfs_exit_compress(void)
+{
+ btrfs_cleanup_workspace_manager(BTRFS_COMPRESS_NONE);
+ btrfs_cleanup_workspace_manager(BTRFS_COMPRESS_ZLIB);
+ btrfs_cleanup_workspace_manager(BTRFS_COMPRESS_LZO);
+ zstd_cleanup_workspace_manager();
+}
+
+/*
+ * Copy decompressed data from working buffer to pages.
+ *
+ * @buf: The decompressed data buffer
+ * @buf_len: The decompressed data length
+ * @decompressed: Number of bytes that are already decompressed inside the
+ * compressed extent
+ * @cb: The compressed extent descriptor
+ * @orig_bio: The original bio that the caller wants to read for
+ *
+ * An easier to understand graph is like below:
+ *
+ * |<- orig_bio ->| |<- orig_bio->|
+ * |<------- full decompressed extent ----->|
+ * |<----------- @cb range ---->|
+ * | |<-- @buf_len -->|
+ * |<--- @decompressed --->|
+ *
+ * Note that, @cb can be a subpage of the full decompressed extent, but
+ * @cb->start always has the same as the orig_file_offset value of the full
+ * decompressed extent.
+ *
+ * When reading compressed extent, we have to read the full compressed extent,
+ * while @orig_bio may only want part of the range.
+ * Thus this function will ensure only data covered by @orig_bio will be copied
+ * to.
+ *
+ * Return 0 if we have copied all needed contents for @orig_bio.
+ * Return >0 if we need continue decompress.
+ */
+int btrfs_decompress_buf2page(const char *buf, u32 buf_len,
+ struct compressed_bio *cb, u32 decompressed)
+{
+ struct bio *orig_bio = cb->orig_bio;
+ /* Offset inside the full decompressed extent */
+ u32 cur_offset;
+
+ cur_offset = decompressed;
+ /* The main loop to do the copy */
+ while (cur_offset < decompressed + buf_len) {
+ struct bio_vec bvec;
+ size_t copy_len;
+ u32 copy_start;
+ /* Offset inside the full decompressed extent */
+ u32 bvec_offset;
+
+ bvec = bio_iter_iovec(orig_bio, orig_bio->bi_iter);
+ /*
+ * cb->start may underflow, but subtracting that value can still
+ * give us correct offset inside the full decompressed extent.
+ */
+ bvec_offset = page_offset(bvec.bv_page) + bvec.bv_offset - cb->start;
+
+ /* Haven't reached the bvec range, exit */
+ if (decompressed + buf_len <= bvec_offset)
+ return 1;
+
+ copy_start = max(cur_offset, bvec_offset);
+ copy_len = min(bvec_offset + bvec.bv_len,
+ decompressed + buf_len) - copy_start;
+ ASSERT(copy_len);
+
+ /*
+ * Extra range check to ensure we didn't go beyond
+ * @buf + @buf_len.
+ */
+ ASSERT(copy_start - decompressed < buf_len);
+ memcpy_to_page(bvec.bv_page, bvec.bv_offset,
+ buf + copy_start - decompressed, copy_len);
+ cur_offset += copy_len;
+
+ bio_advance(orig_bio, copy_len);
+ /* Finished the bio */
+ if (!orig_bio->bi_iter.bi_size)
+ return 0;
+ }
+ return 1;
+}
+
+/*
+ * Shannon Entropy calculation
+ *
+ * Pure byte distribution analysis fails to determine compressibility of data.
+ * Try calculating entropy to estimate the average minimum number of bits
+ * needed to encode the sampled data.
+ *
+ * For convenience, return the percentage of needed bits, instead of amount of
+ * bits directly.
+ *
+ * @ENTROPY_LVL_ACEPTABLE - below that threshold, sample has low byte entropy
+ * and can be compressible with high probability
+ *
+ * @ENTROPY_LVL_HIGH - data are not compressible with high probability
+ *
+ * Use of ilog2() decreases precision, we lower the LVL to 5 to compensate.
+ */
+#define ENTROPY_LVL_ACEPTABLE (65)
+#define ENTROPY_LVL_HIGH (80)
+
+/*
+ * For increasead precision in shannon_entropy calculation,
+ * let's do pow(n, M) to save more digits after comma:
+ *
+ * - maximum int bit length is 64
+ * - ilog2(MAX_SAMPLE_SIZE) -> 13
+ * - 13 * 4 = 52 < 64 -> M = 4
+ *
+ * So use pow(n, 4).
+ */
+static inline u32 ilog2_w(u64 n)
+{
+ return ilog2(n * n * n * n);
+}
+
+static u32 shannon_entropy(struct heuristic_ws *ws)
+{
+ const u32 entropy_max = 8 * ilog2_w(2);
+ u32 entropy_sum = 0;
+ u32 p, p_base, sz_base;
+ u32 i;
+
+ sz_base = ilog2_w(ws->sample_size);
+ for (i = 0; i < BUCKET_SIZE && ws->bucket[i].count > 0; i++) {
+ p = ws->bucket[i].count;
+ p_base = ilog2_w(p);
+ entropy_sum += p * (sz_base - p_base);
+ }
+
+ entropy_sum /= ws->sample_size;
+ return entropy_sum * 100 / entropy_max;
+}
+
+#define RADIX_BASE 4U
+#define COUNTERS_SIZE (1U << RADIX_BASE)
+
+static u8 get4bits(u64 num, int shift) {
+ u8 low4bits;
+
+ num >>= shift;
+ /* Reverse order */
+ low4bits = (COUNTERS_SIZE - 1) - (num % COUNTERS_SIZE);
+ return low4bits;
+}
+
+/*
+ * Use 4 bits as radix base
+ * Use 16 u32 counters for calculating new position in buf array
+ *
+ * @array - array that will be sorted
+ * @array_buf - buffer array to store sorting results
+ * must be equal in size to @array
+ * @num - array size
+ */
+static void radix_sort(struct bucket_item *array, struct bucket_item *array_buf,
+ int num)
+{
+ u64 max_num;
+ u64 buf_num;
+ u32 counters[COUNTERS_SIZE];
+ u32 new_addr;
+ u32 addr;
+ int bitlen;
+ int shift;
+ int i;
+
+ /*
+ * Try avoid useless loop iterations for small numbers stored in big
+ * counters. Example: 48 33 4 ... in 64bit array
+ */
+ max_num = array[0].count;
+ for (i = 1; i < num; i++) {
+ buf_num = array[i].count;
+ if (buf_num > max_num)
+ max_num = buf_num;
+ }
+
+ buf_num = ilog2(max_num);
+ bitlen = ALIGN(buf_num, RADIX_BASE * 2);
+
+ shift = 0;
+ while (shift < bitlen) {
+ memset(counters, 0, sizeof(counters));
+
+ for (i = 0; i < num; i++) {
+ buf_num = array[i].count;
+ addr = get4bits(buf_num, shift);
+ counters[addr]++;
+ }
+
+ for (i = 1; i < COUNTERS_SIZE; i++)
+ counters[i] += counters[i - 1];
+
+ for (i = num - 1; i >= 0; i--) {
+ buf_num = array[i].count;
+ addr = get4bits(buf_num, shift);
+ counters[addr]--;
+ new_addr = counters[addr];
+ array_buf[new_addr] = array[i];
+ }
+
+ shift += RADIX_BASE;
+
+ /*
+ * Normal radix expects to move data from a temporary array, to
+ * the main one. But that requires some CPU time. Avoid that
+ * by doing another sort iteration to original array instead of
+ * memcpy()
+ */
+ memset(counters, 0, sizeof(counters));
+
+ for (i = 0; i < num; i ++) {
+ buf_num = array_buf[i].count;
+ addr = get4bits(buf_num, shift);
+ counters[addr]++;
+ }
+
+ for (i = 1; i < COUNTERS_SIZE; i++)
+ counters[i] += counters[i - 1];
+
+ for (i = num - 1; i >= 0; i--) {
+ buf_num = array_buf[i].count;
+ addr = get4bits(buf_num, shift);
+ counters[addr]--;
+ new_addr = counters[addr];
+ array[new_addr] = array_buf[i];
+ }
+
+ shift += RADIX_BASE;
+ }
+}
+
+/*
+ * Size of the core byte set - how many bytes cover 90% of the sample
+ *
+ * There are several types of structured binary data that use nearly all byte
+ * values. The distribution can be uniform and counts in all buckets will be
+ * nearly the same (eg. encrypted data). Unlikely to be compressible.
+ *
+ * Other possibility is normal (Gaussian) distribution, where the data could
+ * be potentially compressible, but we have to take a few more steps to decide
+ * how much.
+ *
+ * @BYTE_CORE_SET_LOW - main part of byte values repeated frequently,
+ * compression algo can easy fix that
+ * @BYTE_CORE_SET_HIGH - data have uniform distribution and with high
+ * probability is not compressible
+ */
+#define BYTE_CORE_SET_LOW (64)
+#define BYTE_CORE_SET_HIGH (200)
+
+static int byte_core_set_size(struct heuristic_ws *ws)
+{
+ u32 i;
+ u32 coreset_sum = 0;
+ const u32 core_set_threshold = ws->sample_size * 90 / 100;
+ struct bucket_item *bucket = ws->bucket;
+
+ /* Sort in reverse order */
+ radix_sort(ws->bucket, ws->bucket_b, BUCKET_SIZE);
+
+ for (i = 0; i < BYTE_CORE_SET_LOW; i++)
+ coreset_sum += bucket[i].count;
+
+ if (coreset_sum > core_set_threshold)
+ return i;
+
+ for (; i < BYTE_CORE_SET_HIGH && bucket[i].count > 0; i++) {
+ coreset_sum += bucket[i].count;
+ if (coreset_sum > core_set_threshold)
+ break;
+ }
+
+ return i;
+}
+
+/*
+ * Count byte values in buckets.
+ * This heuristic can detect textual data (configs, xml, json, html, etc).
+ * Because in most text-like data byte set is restricted to limited number of
+ * possible characters, and that restriction in most cases makes data easy to
+ * compress.
+ *
+ * @BYTE_SET_THRESHOLD - consider all data within this byte set size:
+ * less - compressible
+ * more - need additional analysis
+ */
+#define BYTE_SET_THRESHOLD (64)
+
+static u32 byte_set_size(const struct heuristic_ws *ws)
+{
+ u32 i;
+ u32 byte_set_size = 0;
+
+ for (i = 0; i < BYTE_SET_THRESHOLD; i++) {
+ if (ws->bucket[i].count > 0)
+ byte_set_size++;
+ }
+
+ /*
+ * Continue collecting count of byte values in buckets. If the byte
+ * set size is bigger then the threshold, it's pointless to continue,
+ * the detection technique would fail for this type of data.
+ */
+ for (; i < BUCKET_SIZE; i++) {
+ if (ws->bucket[i].count > 0) {
+ byte_set_size++;
+ if (byte_set_size > BYTE_SET_THRESHOLD)
+ return byte_set_size;
+ }
+ }
+
+ return byte_set_size;
+}
+
+static bool sample_repeated_patterns(struct heuristic_ws *ws)
+{
+ const u32 half_of_sample = ws->sample_size / 2;
+ const u8 *data = ws->sample;
+
+ return memcmp(&data[0], &data[half_of_sample], half_of_sample) == 0;
+}
+
+static void heuristic_collect_sample(struct inode *inode, u64 start, u64 end,
+ struct heuristic_ws *ws)
+{
+ struct page *page;
+ u64 index, index_end;
+ u32 i, curr_sample_pos;
+ u8 *in_data;
+
+ /*
+ * Compression handles the input data by chunks of 128KiB
+ * (defined by BTRFS_MAX_UNCOMPRESSED)
+ *
+ * We do the same for the heuristic and loop over the whole range.
+ *
+ * MAX_SAMPLE_SIZE - calculated under assumption that heuristic will
+ * process no more than BTRFS_MAX_UNCOMPRESSED at a time.
+ */
+ if (end - start > BTRFS_MAX_UNCOMPRESSED)
+ end = start + BTRFS_MAX_UNCOMPRESSED;
+
+ index = start >> PAGE_SHIFT;
+ index_end = end >> PAGE_SHIFT;
+
+ /* Don't miss unaligned end */
+ if (!IS_ALIGNED(end, PAGE_SIZE))
+ index_end++;
+
+ curr_sample_pos = 0;
+ while (index < index_end) {
+ page = find_get_page(inode->i_mapping, index);
+ in_data = kmap_local_page(page);
+ /* Handle case where the start is not aligned to PAGE_SIZE */
+ i = start % PAGE_SIZE;
+ while (i < PAGE_SIZE - SAMPLING_READ_SIZE) {
+ /* Don't sample any garbage from the last page */
+ if (start > end - SAMPLING_READ_SIZE)
+ break;
+ memcpy(&ws->sample[curr_sample_pos], &in_data[i],
+ SAMPLING_READ_SIZE);
+ i += SAMPLING_INTERVAL;
+ start += SAMPLING_INTERVAL;
+ curr_sample_pos += SAMPLING_READ_SIZE;
+ }
+ kunmap_local(in_data);
+ put_page(page);
+
+ index++;
+ }
+
+ ws->sample_size = curr_sample_pos;
+}
+
+/*
+ * Compression heuristic.
+ *
+ * For now is's a naive and optimistic 'return true', we'll extend the logic to
+ * quickly (compared to direct compression) detect data characteristics
+ * (compressible/uncompressible) to avoid wasting CPU time on uncompressible
+ * data.
+ *
+ * The following types of analysis can be performed:
+ * - detect mostly zero data
+ * - detect data with low "byte set" size (text, etc)
+ * - detect data with low/high "core byte" set
+ *
+ * Return non-zero if the compression should be done, 0 otherwise.
+ */
+int btrfs_compress_heuristic(struct inode *inode, u64 start, u64 end)
+{
+ struct list_head *ws_list = get_workspace(0, 0);
+ struct heuristic_ws *ws;
+ u32 i;
+ u8 byte;
+ int ret = 0;
+
+ ws = list_entry(ws_list, struct heuristic_ws, list);
+
+ heuristic_collect_sample(inode, start, end, ws);
+
+ if (sample_repeated_patterns(ws)) {
+ ret = 1;
+ goto out;
+ }
+
+ memset(ws->bucket, 0, sizeof(*ws->bucket)*BUCKET_SIZE);
+
+ for (i = 0; i < ws->sample_size; i++) {
+ byte = ws->sample[i];
+ ws->bucket[byte].count++;
+ }
+
+ i = byte_set_size(ws);
+ if (i < BYTE_SET_THRESHOLD) {
+ ret = 2;
+ goto out;
+ }
+
+ i = byte_core_set_size(ws);
+ if (i <= BYTE_CORE_SET_LOW) {
+ ret = 3;
+ goto out;
+ }
+
+ if (i >= BYTE_CORE_SET_HIGH) {
+ ret = 0;
+ goto out;
+ }
+
+ i = shannon_entropy(ws);
+ if (i <= ENTROPY_LVL_ACEPTABLE) {
+ ret = 4;
+ goto out;
+ }
+
+ /*
+ * For the levels below ENTROPY_LVL_HIGH, additional analysis would be
+ * needed to give green light to compression.
+ *
+ * For now just assume that compression at that level is not worth the
+ * resources because:
+ *
+ * 1. it is possible to defrag the data later
+ *
+ * 2. the data would turn out to be hardly compressible, eg. 150 byte
+ * values, every bucket has counter at level ~54. The heuristic would
+ * be confused. This can happen when data have some internal repeated
+ * patterns like "abbacbbc...". This can be detected by analyzing
+ * pairs of bytes, which is too costly.
+ */
+ if (i < ENTROPY_LVL_HIGH) {
+ ret = 5;
+ goto out;
+ } else {
+ ret = 0;
+ goto out;
+ }
+
+out:
+ put_workspace(0, ws_list);
+ return ret;
+}
+
+/*
+ * Convert the compression suffix (eg. after "zlib" starting with ":") to
+ * level, unrecognized string will set the default level
+ */
+unsigned int btrfs_compress_str2level(unsigned int type, const char *str)
+{
+ unsigned int level = 0;
+ int ret;
+
+ if (!type)
+ return 0;
+
+ if (str[0] == ':') {
+ ret = kstrtouint(str + 1, 10, &level);
+ if (ret)
+ level = 0;
+ }
+
+ level = btrfs_compress_set_level(type, level);
+
+ return level;
+}