On 2017-08-09 22:39, Nick Terrell wrote:
Add zstd compression and decompression support to BtrFS. zstd at its
fastest level compresses almost as well as zlib, while offering much
faster compression and decompression, approaching lzo speeds.

I benchmarked btrfs with zstd compression against no compression, lzo
compression, and zlib compression. I benchmarked two scenarios. Copying
a set of files to btrfs, and then reading the files. Copying a tarball
to btrfs, extracting it to btrfs, and then reading the extracted files.
After every operation, I call `sync` and include the sync time.
Between every pair of operations I unmount and remount the filesystem
to avoid caching. The benchmark files can be found in the upstream
zstd source repository under
`contrib/linux-kernel/{btrfs-benchmark.sh,btrfs-extract-benchmark.sh}`
[1] [2].

I ran the benchmarks on a Ubuntu 14.04 VM with 2 cores and 4 GiB of RAM.
The VM is running on a MacBook Pro with a 3.1 GHz Intel Core i7 processor,
16 GB of RAM, and a SSD.

The first compression benchmark is copying 10 copies of the unzipped
Silesia corpus [3] into a BtrFS filesystem mounted with
`-o compress-force=Method`. The decompression benchmark times how long
it takes to `tar` all 10 copies into `/dev/null`. The compression ratio is
measured by comparing the output of `df` and `du`. See the benchmark file
[1] for details. I benchmarked multiple zstd compression levels, although
the patch uses zstd level 1.

| Method  | Ratio | Compression MB/s | Decompression speed |
|---------|-------|------------------|---------------------|
| None    |  0.99 |              504 |                 686 |
| lzo     |  1.66 |              398 |                 442 |
| zlib    |  2.58 |               65 |                 241 |
| zstd 1  |  2.57 |              260 |                 383 |
| zstd 3  |  2.71 |              174 |                 408 |
| zstd 6  |  2.87 |               70 |                 398 |
| zstd 9  |  2.92 |               43 |                 406 |
| zstd 12 |  2.93 |               21 |                 408 |
| zstd 15 |  3.01 |               11 |                 354 |

The next benchmark first copies `linux-4.11.6.tar` [4] to btrfs. Then it
measures the compression ratio, extracts the tar, and deletes the tar.
Then it measures the compression ratio again, and `tar`s the extracted
files into `/dev/null`. See the benchmark file [2] for details.

| Method | Tar Ratio | Extract Ratio | Copy (s) | Extract (s)| Read (s) |
|--------|-----------|---------------|----------|------------|----------|
| None   |      0.97 |          0.78 |    0.981 |      5.501 |    8.807 |
| lzo    |      2.06 |          1.38 |    1.631 |      8.458 |    8.585 |
| zlib   |      3.40 |          1.86 |    7.750 |     21.544 |   11.744 |
| zstd 1 |      3.57 |          1.85 |    2.579 |     11.479 |    9.389 |

[1] 
https://github.com/facebook/zstd/blob/dev/contrib/linux-kernel/btrfs-benchmark.sh
[2] 
https://github.com/facebook/zstd/blob/dev/contrib/linux-kernel/btrfs-extract-benchmark.sh
[3] http://sun.aei.polsl.pl/~sdeor/index.php?page=silesia
[4] https://cdn.kernel.org/pub/linux/kernel/v4.x/linux-4.11.6.tar.xz

zstd source repository: https://github.com/facebook/zstd

Signed-off-by: Nick Terrell <terre...@fb.com>
Considering how things went with the previous patch, I've been a bit more aggressive testing this one, but after now almost 72 hours of combined runtime for each of the architectures I have tests set up for with nothing breaking (well, nothing breaking that wasn't already breaking before this patch set, some of the raid56 tests are still failing semi-reliably as expected), I'd say this is reasonably stable and looks good overall.
---
v2 -> v3:
- Port upstream BtrFS commits e1ddce71d6, 389a6cfc2a, and 6acafd1eff
- Change default compression level for BtrFS to 3

v3 -> v4:
- Add missing includes, which fixes the aarch64 build
- Fix minor linter warnings

  fs/btrfs/Kconfig           |   2 +
  fs/btrfs/Makefile          |   2 +-
  fs/btrfs/compression.c     |   1 +
  fs/btrfs/compression.h     |   6 +-
  fs/btrfs/ctree.h           |   1 +
  fs/btrfs/disk-io.c         |   2 +
  fs/btrfs/ioctl.c           |   6 +-
  fs/btrfs/props.c           |   6 +
  fs/btrfs/super.c           |  12 +-
  fs/btrfs/sysfs.c           |   2 +
  fs/btrfs/zstd.c            | 432 +++++++++++++++++++++++++++++++++++++++++++++
  include/uapi/linux/btrfs.h |   8 +-
  12 files changed, 468 insertions(+), 12 deletions(-)
  create mode 100644 fs/btrfs/zstd.c

diff --git a/fs/btrfs/Kconfig b/fs/btrfs/Kconfig
index 80e9c18..a26c63b 100644
--- a/fs/btrfs/Kconfig
+++ b/fs/btrfs/Kconfig
@@ -6,6 +6,8 @@ config BTRFS_FS
        select ZLIB_DEFLATE
        select LZO_COMPRESS
        select LZO_DECOMPRESS
+       select ZSTD_COMPRESS
+       select ZSTD_DECOMPRESS
        select RAID6_PQ
        select XOR_BLOCKS
        select SRCU
diff --git a/fs/btrfs/Makefile b/fs/btrfs/Makefile
index 128ce17..962a95a 100644
--- a/fs/btrfs/Makefile
+++ b/fs/btrfs/Makefile
@@ -6,7 +6,7 @@ btrfs-y += super.o ctree.o extent-tree.o print-tree.o 
root-tree.o dir-item.o \
           transaction.o inode.o file.o tree-defrag.o \
           extent_map.o sysfs.o struct-funcs.o xattr.o ordered-data.o \
           extent_io.o volumes.o async-thread.o ioctl.o locking.o orphan.o \
-          export.o tree-log.o free-space-cache.o zlib.o lzo.o \
+          export.o tree-log.o free-space-cache.o zlib.o lzo.o zstd.o \
           compression.o delayed-ref.o relocation.o delayed-inode.o scrub.o \
           reada.o backref.o ulist.o qgroup.o send.o dev-replace.o raid56.o \
           uuid-tree.o props.o hash.o free-space-tree.o
diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
index d2ef9ac..4ff42d1 100644
--- a/fs/btrfs/compression.c
+++ b/fs/btrfs/compression.c
@@ -704,6 +704,7 @@ static struct {
  static const struct btrfs_compress_op * const btrfs_compress_op[] = {
        &btrfs_zlib_compress,
        &btrfs_lzo_compress,
+       &btrfs_zstd_compress,
  };

  void __init btrfs_init_compress(void)
diff --git a/fs/btrfs/compression.h b/fs/btrfs/compression.h
index 87f6d33..2269e00 100644
--- a/fs/btrfs/compression.h
+++ b/fs/btrfs/compression.h
@@ -99,8 +99,9 @@ enum btrfs_compression_type {
        BTRFS_COMPRESS_NONE  = 0,
        BTRFS_COMPRESS_ZLIB  = 1,
        BTRFS_COMPRESS_LZO   = 2,
-       BTRFS_COMPRESS_TYPES = 2,
-       BTRFS_COMPRESS_LAST  = 3,
+       BTRFS_COMPRESS_ZSTD  = 3,
+       BTRFS_COMPRESS_TYPES = 3,
+       BTRFS_COMPRESS_LAST  = 4,
  };

  struct btrfs_compress_op {
@@ -128,5 +129,6 @@ struct btrfs_compress_op {

  extern const struct btrfs_compress_op btrfs_zlib_compress;
  extern const struct btrfs_compress_op btrfs_lzo_compress;
+extern const struct btrfs_compress_op btrfs_zstd_compress;

  #endif
diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 3f3eb7b..845d77c 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -270,6 +270,7 @@ struct btrfs_super_block {
         BTRFS_FEATURE_INCOMPAT_MIXED_GROUPS |          \
         BTRFS_FEATURE_INCOMPAT_BIG_METADATA |          \
         BTRFS_FEATURE_INCOMPAT_COMPRESS_LZO |          \
+        BTRFS_FEATURE_INCOMPAT_COMPRESS_ZSTD |         \
         BTRFS_FEATURE_INCOMPAT_RAID56 |                \
         BTRFS_FEATURE_INCOMPAT_EXTENDED_IREF |         \
         BTRFS_FEATURE_INCOMPAT_SKINNY_METADATA |       \
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 080e2eb..04632f4 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -2828,6 +2828,8 @@ int open_ctree(struct super_block *sb,
        features |= BTRFS_FEATURE_INCOMPAT_MIXED_BACKREF;
        if (fs_info->compress_type == BTRFS_COMPRESS_LZO)
                features |= BTRFS_FEATURE_INCOMPAT_COMPRESS_LZO;
+       else if (fs_info->compress_type == BTRFS_COMPRESS_ZSTD)
+               features |= BTRFS_FEATURE_INCOMPAT_COMPRESS_ZSTD;

        if (features & BTRFS_FEATURE_INCOMPAT_SKINNY_METADATA)
                btrfs_info(fs_info, "has skinny extents");
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index fa1b78c..b9963d9 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -327,8 +327,10 @@ static int btrfs_ioctl_setflags(struct file *file, void 
__user *arg)

                if (fs_info->compress_type == BTRFS_COMPRESS_LZO)
                        comp = "lzo";
-               else
+               else if (fs_info->compress_type == BTRFS_COMPRESS_ZLIB)
                        comp = "zlib";
+               else
+                       comp = "zstd";
                ret = btrfs_set_prop(inode, "btrfs.compression",
                                     comp, strlen(comp), 0);
                if (ret)
@@ -1466,6 +1468,8 @@ int btrfs_defrag_file(struct inode *inode, struct file 
*file,

        if (range->compress_type == BTRFS_COMPRESS_LZO) {
                btrfs_set_fs_incompat(fs_info, COMPRESS_LZO);
+       } else if (range->compress_type == BTRFS_COMPRESS_ZSTD) {
+               btrfs_set_fs_incompat(fs_info, COMPRESS_ZSTD);
        }

        ret = defrag_count;
diff --git a/fs/btrfs/props.c b/fs/btrfs/props.c
index 4b23ae5..20631e9 100644
--- a/fs/btrfs/props.c
+++ b/fs/btrfs/props.c
@@ -390,6 +390,8 @@ static int prop_compression_validate(const char *value, 
size_t len)
                return 0;
        else if (!strncmp("zlib", value, len))
                return 0;
+       else if (!strncmp("zstd", value, len))
+               return 0;

        return -EINVAL;
  }
@@ -412,6 +414,8 @@ static int prop_compression_apply(struct inode *inode,
                type = BTRFS_COMPRESS_LZO;
        else if (!strncmp("zlib", value, len))
                type = BTRFS_COMPRESS_ZLIB;
+       else if (!strncmp("zstd", value, len))
+               type = BTRFS_COMPRESS_ZSTD;
        else
                return -EINVAL;

@@ -429,6 +433,8 @@ static const char *prop_compression_extract(struct inode 
*inode)
                return "zlib";
        case BTRFS_COMPRESS_LZO:
                return "lzo";
+       case BTRFS_COMPRESS_ZSTD:
+               return "zstd";
        }

        return NULL;
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 12540b6..c370dea 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -513,6 +513,14 @@ int btrfs_parse_options(struct btrfs_fs_info *info, char 
*options,
                                btrfs_clear_opt(info->mount_opt, NODATASUM);
                                btrfs_set_fs_incompat(info, COMPRESS_LZO);
                                no_compress = 0;
+                       } else if (strcmp(args[0].from, "zstd") == 0) {
+                               compress_type = "zstd";
+                               info->compress_type = BTRFS_COMPRESS_ZSTD;
+                               btrfs_set_opt(info->mount_opt, COMPRESS);
+                               btrfs_clear_opt(info->mount_opt, NODATACOW);
+                               btrfs_clear_opt(info->mount_opt, NODATASUM);
+                               btrfs_set_fs_incompat(info, COMPRESS_ZSTD);
+                               no_compress = 0;
                        } else if (strncmp(args[0].from, "no", 2) == 0) {
                                compress_type = "no";
                                btrfs_clear_opt(info->mount_opt, COMPRESS);
@@ -1227,8 +1235,10 @@ static int btrfs_show_options(struct seq_file *seq, 
struct dentry *dentry)
        if (btrfs_test_opt(info, COMPRESS)) {
                if (info->compress_type == BTRFS_COMPRESS_ZLIB)
                        compress_type = "zlib";
-               else
+               else if (info->compress_type == BTRFS_COMPRESS_LZO)
                        compress_type = "lzo";
+               else
+                       compress_type = "zstd";
                if (btrfs_test_opt(info, FORCE_COMPRESS))
                        seq_printf(seq, ",compress-force=%s", compress_type);
                else
diff --git a/fs/btrfs/sysfs.c b/fs/btrfs/sysfs.c
index c2d5f35..2b6d37c 100644
--- a/fs/btrfs/sysfs.c
+++ b/fs/btrfs/sysfs.c
@@ -200,6 +200,7 @@ BTRFS_FEAT_ATTR_INCOMPAT(mixed_backref, MIXED_BACKREF);
  BTRFS_FEAT_ATTR_INCOMPAT(default_subvol, DEFAULT_SUBVOL);
  BTRFS_FEAT_ATTR_INCOMPAT(mixed_groups, MIXED_GROUPS);
  BTRFS_FEAT_ATTR_INCOMPAT(compress_lzo, COMPRESS_LZO);
+BTRFS_FEAT_ATTR_INCOMPAT(compress_zstd, COMPRESS_ZSTD);
  BTRFS_FEAT_ATTR_INCOMPAT(big_metadata, BIG_METADATA);
  BTRFS_FEAT_ATTR_INCOMPAT(extended_iref, EXTENDED_IREF);
  BTRFS_FEAT_ATTR_INCOMPAT(raid56, RAID56);
@@ -212,6 +213,7 @@ static struct attribute *btrfs_supported_feature_attrs[] = {
        BTRFS_FEAT_ATTR_PTR(default_subvol),
        BTRFS_FEAT_ATTR_PTR(mixed_groups),
        BTRFS_FEAT_ATTR_PTR(compress_lzo),
+       BTRFS_FEAT_ATTR_PTR(compress_zstd),
        BTRFS_FEAT_ATTR_PTR(big_metadata),
        BTRFS_FEAT_ATTR_PTR(extended_iref),
        BTRFS_FEAT_ATTR_PTR(raid56),
diff --git a/fs/btrfs/zstd.c b/fs/btrfs/zstd.c
new file mode 100644
index 0000000..607ce47
--- /dev/null
+++ b/fs/btrfs/zstd.c
@@ -0,0 +1,432 @@
+/*
+ * Copyright (c) 2016-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public
+ * License v2 as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ */
+#include <linux/bio.h>
+#include <linux/err.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/mm.h>
+#include <linux/pagemap.h>
+#include <linux/refcount.h>
+#include <linux/sched.h>
+#include <linux/slab.h>
+#include <linux/zstd.h>
+#include "compression.h"
+
+#define ZSTD_BTRFS_MAX_WINDOWLOG 17
+#define ZSTD_BTRFS_MAX_INPUT (1 << ZSTD_BTRFS_MAX_WINDOWLOG)
+#define ZSTD_BTRFS_DEFAULT_LEVEL 3
+
+static ZSTD_parameters zstd_get_btrfs_parameters(size_t src_len)
+{
+       ZSTD_parameters params = ZSTD_getParams(ZSTD_BTRFS_DEFAULT_LEVEL,
+                                               src_len, 0);
+
+       if (params.cParams.windowLog > ZSTD_BTRFS_MAX_WINDOWLOG)
+               params.cParams.windowLog = ZSTD_BTRFS_MAX_WINDOWLOG;
+       WARN_ON(src_len > ZSTD_BTRFS_MAX_INPUT);
+       return params;
+}
+
+struct workspace {
+       void *mem;
+       size_t size;
+       char *buf;
+       struct list_head list;
+};
+
+static void zstd_free_workspace(struct list_head *ws)
+{
+       struct workspace *workspace = list_entry(ws, struct workspace, list);
+
+       kvfree(workspace->mem);
+       kfree(workspace->buf);
+       kfree(workspace);
+}
+
+static struct list_head *zstd_alloc_workspace(void)
+{
+       ZSTD_parameters params =
+                       zstd_get_btrfs_parameters(ZSTD_BTRFS_MAX_INPUT);
+       struct workspace *workspace;
+
+       workspace = kzalloc(sizeof(*workspace), GFP_KERNEL);
+       if (!workspace)
+               return ERR_PTR(-ENOMEM);
+
+       workspace->size = max_t(size_t,
+                       ZSTD_CStreamWorkspaceBound(params.cParams),
+                       ZSTD_DStreamWorkspaceBound(ZSTD_BTRFS_MAX_INPUT));
+       workspace->mem = kvmalloc(workspace->size, GFP_KERNEL);
+       workspace->buf = kmalloc(PAGE_SIZE, GFP_KERNEL);
+       if (!workspace->mem || !workspace->buf)
+               goto fail;
+
+       INIT_LIST_HEAD(&workspace->list);
+
+       return &workspace->list;
+fail:
+       zstd_free_workspace(&workspace->list);
+       return ERR_PTR(-ENOMEM);
+}
+
+static int zstd_compress_pages(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)
+{
+       struct workspace *workspace = list_entry(ws, struct workspace, list);
+       ZSTD_CStream *stream;
+       int ret = 0;
+       int nr_pages = 0;
+       struct page *in_page = NULL;  /* The current page to read */
+       struct page *out_page = NULL; /* The current page to write to */
+       ZSTD_inBuffer in_buf = { NULL, 0, 0 };
+       ZSTD_outBuffer out_buf = { NULL, 0, 0 };
+       unsigned long tot_in = 0;
+       unsigned long tot_out = 0;
+       unsigned long len = *total_out;
+       const unsigned long nr_dest_pages = *out_pages;
+       unsigned long max_out = nr_dest_pages * PAGE_SIZE;
+       ZSTD_parameters params = zstd_get_btrfs_parameters(len);
+
+       *out_pages = 0;
+       *total_out = 0;
+       *total_in = 0;
+
+       /* Initialize the stream */
+       stream = ZSTD_initCStream(params, len, workspace->mem,
+                       workspace->size);
+       if (!stream) {
+               pr_warn("BTRFS: ZSTD_initCStream failed\n");
+               ret = -EIO;
+               goto out;
+       }
+
+       /* map in the first page of input data */
+       in_page = find_get_page(mapping, start >> PAGE_SHIFT);
+       in_buf.src = kmap(in_page);
+       in_buf.pos = 0;
+       in_buf.size = min_t(size_t, len, PAGE_SIZE);
+
+
+       /* Allocate and map in the output buffer */
+       out_page = alloc_page(GFP_NOFS | __GFP_HIGHMEM);
+       if (out_page == NULL) {
+               ret = -ENOMEM;
+               goto out;
+       }
+       pages[nr_pages++] = out_page;
+       out_buf.dst = kmap(out_page);
+       out_buf.pos = 0;
+       out_buf.size = min_t(size_t, max_out, PAGE_SIZE);
+
+       while (1) {
+               size_t ret2;
+
+               ret2 = ZSTD_compressStream(stream, &out_buf, &in_buf);
+               if (ZSTD_isError(ret2)) {
+                       pr_debug("BTRFS: ZSTD_compressStream returned %d\n",
+                                       ZSTD_getErrorCode(ret2));
+                       ret = -EIO;
+                       goto out;
+               }
+
+               /* Check to see if we are making it bigger */
+               if (tot_in + in_buf.pos > 8192 &&
+                               tot_in + in_buf.pos <
+                               tot_out + out_buf.pos) {
+                       ret = -E2BIG;
+                       goto out;
+               }
+
+               /* We've reached the end of our output range */
+               if (out_buf.pos >= max_out) {
+                       tot_out += out_buf.pos;
+                       ret = -E2BIG;
+                       goto out;
+               }
+
+               /* Check if we need more output space */
+               if (out_buf.pos == out_buf.size) {
+                       tot_out += PAGE_SIZE;
+                       max_out -= PAGE_SIZE;
+                       kunmap(out_page);
+                       if (nr_pages == nr_dest_pages) {
+                               out_page = NULL;
+                               ret = -E2BIG;
+                               goto out;
+                       }
+                       out_page = alloc_page(GFP_NOFS | __GFP_HIGHMEM);
+                       if (out_page == NULL) {
+                               ret = -ENOMEM;
+                               goto out;
+                       }
+                       pages[nr_pages++] = out_page;
+                       out_buf.dst = kmap(out_page);
+                       out_buf.pos = 0;
+                       out_buf.size = min_t(size_t, max_out, PAGE_SIZE);
+               }
+
+               /* We've reached the end of the input */
+               if (in_buf.pos >= len) {
+                       tot_in += in_buf.pos;
+                       break;
+               }
+
+               /* Check if we need more input */
+               if (in_buf.pos == in_buf.size) {
+                       tot_in += PAGE_SIZE;
+                       kunmap(in_page);
+                       put_page(in_page);
+
+                       start += PAGE_SIZE;
+                       len -= PAGE_SIZE;
+                       in_page = find_get_page(mapping, start >> PAGE_SHIFT);
+                       in_buf.src = kmap(in_page);
+                       in_buf.pos = 0;
+                       in_buf.size = min_t(size_t, len, PAGE_SIZE);
+               }
+       }
+       while (1) {
+               size_t ret2;
+
+               ret2 = ZSTD_endStream(stream, &out_buf);
+               if (ZSTD_isError(ret2)) {
+                       pr_debug("BTRFS: ZSTD_endStream returned %d\n",
+                                       ZSTD_getErrorCode(ret2));
+                       ret = -EIO;
+                       goto out;
+               }
+               if (ret2 == 0) {
+                       tot_out += out_buf.pos;
+                       break;
+               }
+               if (out_buf.pos >= max_out) {
+                       tot_out += out_buf.pos;
+                       ret = -E2BIG;
+                       goto out;
+               }
+
+               tot_out += PAGE_SIZE;
+               max_out -= PAGE_SIZE;
+               kunmap(out_page);
+               if (nr_pages == nr_dest_pages) {
+                       out_page = NULL;
+                       ret = -E2BIG;
+                       goto out;
+               }
+               out_page = alloc_page(GFP_NOFS | __GFP_HIGHMEM);
+               if (out_page == NULL) {
+                       ret = -ENOMEM;
+                       goto out;
+               }
+               pages[nr_pages++] = out_page;
+               out_buf.dst = kmap(out_page);
+               out_buf.pos = 0;
+               out_buf.size = min_t(size_t, max_out, PAGE_SIZE);
+       }
+
+       if (tot_out >= tot_in) {
+               ret = -E2BIG;
+               goto out;
+       }
+
+       ret = 0;
+       *total_in = tot_in;
+       *total_out = tot_out;
+out:
+       *out_pages = nr_pages;
+       /* Cleanup */
+       if (in_page) {
+               kunmap(in_page);
+               put_page(in_page);
+       }
+       if (out_page)
+               kunmap(out_page);
+       return ret;
+}
+
+static int zstd_decompress_bio(struct list_head *ws, struct compressed_bio *cb)
+{
+       struct workspace *workspace = list_entry(ws, struct workspace, list);
+       struct page **pages_in = cb->compressed_pages;
+       u64 disk_start = cb->start;
+       struct bio *orig_bio = cb->orig_bio;
+       size_t srclen = cb->compressed_len;
+       ZSTD_DStream *stream;
+       int ret = 0;
+       unsigned long page_in_index = 0;
+       unsigned long total_pages_in = DIV_ROUND_UP(srclen, PAGE_SIZE);
+       unsigned long buf_start;
+       unsigned long total_out = 0;
+       ZSTD_inBuffer in_buf = { NULL, 0, 0 };
+       ZSTD_outBuffer out_buf = { NULL, 0, 0 };
+
+       stream = ZSTD_initDStream(
+                       ZSTD_BTRFS_MAX_INPUT, workspace->mem, workspace->size);
+       if (!stream) {
+               pr_debug("BTRFS: ZSTD_initDStream failed\n");
+               ret = -EIO;
+               goto done;
+       }
+
+       in_buf.src = kmap(pages_in[page_in_index]);
+       in_buf.pos = 0;
+       in_buf.size = min_t(size_t, srclen, PAGE_SIZE);
+
+       out_buf.dst = workspace->buf;
+       out_buf.pos = 0;
+       out_buf.size = PAGE_SIZE;
+
+       while (1) {
+               size_t ret2;
+
+               ret2 = ZSTD_decompressStream(stream, &out_buf, &in_buf);
+               if (ZSTD_isError(ret2)) {
+                       pr_debug("BTRFS: ZSTD_decompressStream returned %d\n",
+                                       ZSTD_getErrorCode(ret2));
+                       ret = -EIO;
+                       goto done;
+               }
+               buf_start = total_out;
+               total_out += out_buf.pos;
+               out_buf.pos = 0;
+
+               ret = btrfs_decompress_buf2page(out_buf.dst, buf_start,
+                               total_out, disk_start, orig_bio);
+               if (ret == 0)
+                       break;
+
+               if (in_buf.pos >= srclen)
+                       break;
+
+               /* Check if we've hit the end of a frame */
+               if (ret2 == 0)
+                       break;
+
+               if (in_buf.pos == in_buf.size) {
+                       kunmap(pages_in[page_in_index++]);
+                       if (page_in_index >= total_pages_in) {
+                               in_buf.src = NULL;
+                               ret = -EIO;
+                               goto done;
+                       }
+                       srclen -= PAGE_SIZE;
+                       in_buf.src = kmap(pages_in[page_in_index]);
+                       in_buf.pos = 0;
+                       in_buf.size = min_t(size_t, srclen, PAGE_SIZE);
+               }
+       }
+       ret = 0;
+       zero_fill_bio(orig_bio);
+done:
+       if (in_buf.src)
+               kunmap(pages_in[page_in_index]);
+       return ret;
+}
+
+static int zstd_decompress(struct list_head *ws, unsigned char *data_in,
+               struct page *dest_page,
+               unsigned long start_byte,
+               size_t srclen, size_t destlen)
+{
+       struct workspace *workspace = list_entry(ws, struct workspace, list);
+       ZSTD_DStream *stream;
+       int ret = 0;
+       size_t ret2;
+       ZSTD_inBuffer in_buf = { NULL, 0, 0 };
+       ZSTD_outBuffer out_buf = { NULL, 0, 0 };
+       unsigned long total_out = 0;
+       unsigned long pg_offset = 0;
+       char *kaddr;
+
+       stream = ZSTD_initDStream(
+                       ZSTD_BTRFS_MAX_INPUT, workspace->mem, workspace->size);
+       if (!stream) {
+               pr_warn("BTRFS: ZSTD_initDStream failed\n");
+               ret = -EIO;
+               goto finish;
+       }
+
+       destlen = min_t(size_t, destlen, PAGE_SIZE);
+
+       in_buf.src = data_in;
+       in_buf.pos = 0;
+       in_buf.size = srclen;
+
+       out_buf.dst = workspace->buf;
+       out_buf.pos = 0;
+       out_buf.size = PAGE_SIZE;
+
+       ret2 = 1;
+       while (pg_offset < destlen && in_buf.pos < in_buf.size) {
+               unsigned long buf_start;
+               unsigned long buf_offset;
+               unsigned long bytes;
+
+               /* Check if the frame is over and we still need more input */
+               if (ret2 == 0) {
+                       pr_debug("BTRFS: ZSTD_decompressStream ended early\n");
+                       ret = -EIO;
+                       goto finish;
+               }
+               ret2 = ZSTD_decompressStream(stream, &out_buf, &in_buf);
+               if (ZSTD_isError(ret2)) {
+                       pr_debug("BTRFS: ZSTD_decompressStream returned %d\n",
+                                       ZSTD_getErrorCode(ret2));
+                       ret = -EIO;
+                       goto finish;
+               }
+
+               buf_start = total_out;
+               total_out += out_buf.pos;
+               out_buf.pos = 0;
+
+               if (total_out <= start_byte)
+                       continue;
+
+               if (total_out > start_byte && buf_start < start_byte)
+                       buf_offset = start_byte - buf_start;
+               else
+                       buf_offset = 0;
+
+               bytes = min_t(unsigned long, destlen - pg_offset,
+                               out_buf.size - buf_offset);
+
+               kaddr = kmap_atomic(dest_page);
+               memcpy(kaddr + pg_offset, out_buf.dst + buf_offset, bytes);
+               kunmap_atomic(kaddr);
+
+               pg_offset += bytes;
+       }
+       ret = 0;
+finish:
+       if (pg_offset < destlen) {
+               kaddr = kmap_atomic(dest_page);
+               memset(kaddr + pg_offset, 0, destlen - pg_offset);
+               kunmap_atomic(kaddr);
+       }
+       return ret;
+}
+
+const struct btrfs_compress_op btrfs_zstd_compress = {
+       .alloc_workspace = zstd_alloc_workspace,
+       .free_workspace = zstd_free_workspace,
+       .compress_pages = zstd_compress_pages,
+       .decompress_bio = zstd_decompress_bio,
+       .decompress = zstd_decompress,
+};
diff --git a/include/uapi/linux/btrfs.h b/include/uapi/linux/btrfs.h
index 9aa74f3..378230c 100644
--- a/include/uapi/linux/btrfs.h
+++ b/include/uapi/linux/btrfs.h
@@ -255,13 +255,7 @@ struct btrfs_ioctl_fs_info_args {
  #define BTRFS_FEATURE_INCOMPAT_DEFAULT_SUBVOL (1ULL << 1)
  #define BTRFS_FEATURE_INCOMPAT_MIXED_GROUPS   (1ULL << 2)
  #define BTRFS_FEATURE_INCOMPAT_COMPRESS_LZO   (1ULL << 3)
-/*
- * some patches floated around with a second compression method
- * lets save that incompat here for when they do get in
- * Note we don't actually support it, we're just reserving the
- * number
- */
-#define BTRFS_FEATURE_INCOMPAT_COMPRESS_LZOv2  (1ULL << 4)
+#define BTRFS_FEATURE_INCOMPAT_COMPRESS_ZSTD   (1ULL << 4)

  /*
   * older kernels tried to do bigger metadata blocks, but the
--
2.9.3


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