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squashfs: Add zstd support

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Add zstd compression and decompression support to SquashFS. zstd is a
great fit for SquashFS because it can compress at ratios approaching xz,
while decompressing twice as fast as zlib. For SquashFS in particular,
it can decompress as fast as lzo and lz4. It also has the flexibility
to turn down the compression ratio for faster compression times.

The compression benchmark is run on the file tree from the SquashFS archive
found in ubuntu-16.10-desktop-amd64.iso [1]. It uses `mksquashfs` with the
default block size (128 KB) and and various compression algorithms/levels.
xz and zstd are also benchmarked with 256 KB blocks. The decompression
benchmark times how long it takes to `tar` the file tree into `/dev/null`.
See the benchmark file in the upstream zstd source repository located under
`contrib/linux-kernel/squashfs-benchmark.sh` [2] for details.

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.

| Method         | Ratio | Compression MB/s | Decompression MB/s |
|----------------|-------|------------------|--------------------|
| gzip           |  2.92 |               15 |                128 |
| lzo            |  2.64 |              9.5 |                217 |
| lz4            |  2.12 |               94 |                218 |
| xz             |  3.43 |              5.5 |                 35 |
| xz 256 KB      |  3.53 |              5.4 |                 40 |
| zstd 1         |  2.71 |               96 |                210 |
| zstd 5         |  2.93 |               69 |                198 |
| zstd 10        |  3.01 |               41 |                225 |
| zstd 15        |  3.13 |             11.4 |                224 |
| zstd 16 256 KB |  3.24 |              8.1 |                210 |

This patch was written by Sean Purcell <me@seanp.xyz>, but I will be
taking over the submission process.

[1] http://releases.ubuntu.com/16.10/
[2] https://github.com/facebook/zstd/blob/dev/contrib/linux-kernel/squashfs-benchmark.sh

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

Signed-off-by: Sean Purcell <me@seanp.xyz>
Signed-off-by: Nick Terrell <terrelln@fb.com>
Signed-off-by: Chris Mason <clm@fb.com>
Acked-by: Phillip Lougher <phillip@squashfs.org.uk>
This commit is contained in:
Sean Purcell 2017-08-09 19:42:36 -07:00 committed by Chris Mason
parent 5c1aab1dd5
commit 87bf54bb43
6 changed files with 178 additions and 0 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

14
fs/squashfs/Kconfig
View file

@ -165,6 +165,20 @@ config SQUASHFS_XZ
If unsure, say N.
config SQUASHFS_ZSTD
bool "Include support for ZSTD compressed file systems"
depends on SQUASHFS
select ZSTD_DECOMPRESS
help
Saying Y here includes support for reading Squashfs file systems
compressed with ZSTD compression. ZSTD gives better compression than
the default ZLIB compression, while using less CPU.
ZSTD is not the standard compression used in Squashfs and so most
file systems will be readable without selecting this option.
If unsure, say N.
config SQUASHFS_4K_DEVBLK_SIZE
bool "Use 4K device block size?"
depends on SQUASHFS

1
fs/squashfs/Makefile
View file

@ -15,3 +15,4 @@ squashfs-$(CONFIG_SQUASHFS_LZ4) += lz4_wrapper.o
squashfs-$(CONFIG_SQUASHFS_LZO) += lzo_wrapper.o
squashfs-$(CONFIG_SQUASHFS_XZ) += xz_wrapper.o
squashfs-$(CONFIG_SQUASHFS_ZLIB) += zlib_wrapper.o
squashfs-$(CONFIG_SQUASHFS_ZSTD) += zstd_wrapper.o

7
fs/squashfs/decompressor.c
View file

@ -65,6 +65,12 @@ static const struct squashfs_decompressor squashfs_zlib_comp_ops = {
};
#endif
#ifndef CONFIG_SQUASHFS_ZSTD
static const struct squashfs_decompressor squashfs_zstd_comp_ops = {
NULL, NULL, NULL, NULL, ZSTD_COMPRESSION, "zstd", 0
};
#endif
static const struct squashfs_decompressor squashfs_unknown_comp_ops = {
NULL, NULL, NULL, NULL, 0, "unknown", 0
};
@ -75,6 +81,7 @@ static const struct squashfs_decompressor *decompressor[] = {
&squashfs_lzo_comp_ops,
&squashfs_xz_comp_ops,
&squashfs_lzma_unsupported_comp_ops,
&squashfs_zstd_comp_ops,
&squashfs_unknown_comp_ops
};

4
fs/squashfs/decompressor.h
View file

@ -58,4 +58,8 @@ extern const struct squashfs_decompressor squashfs_lzo_comp_ops;
extern const struct squashfs_decompressor squashfs_zlib_comp_ops;
#endif
#ifdef CONFIG_SQUASHFS_ZSTD
extern const struct squashfs_decompressor squashfs_zstd_comp_ops;
#endif
#endif

1
fs/squashfs/squashfs_fs.h
View file

@ -241,6 +241,7 @@ struct meta_index {
#define LZO_COMPRESSION 3
#define XZ_COMPRESSION 4
#define LZ4_COMPRESSION 5
#define ZSTD_COMPRESSION 6
struct squashfs_super_block {
__le32 s_magic;

151
fs/squashfs/zstd_wrapper.c Normal file
View file

@ -0,0 +1,151 @@
/*
* Squashfs - a compressed read only filesystem for Linux
*
* 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
* as published by the Free Software Foundation; either version 2,
* or (at your option) any later version.
*
* 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.
*
* zstd_wrapper.c
*/
#include <linux/mutex.h>
#include <linux/buffer_head.h>
#include <linux/slab.h>
#include <linux/zstd.h>
#include <linux/vmalloc.h>
#include "squashfs_fs.h"
#include "squashfs_fs_sb.h"
#include "squashfs.h"
#include "decompressor.h"
#include "page_actor.h"
struct workspace {
void *mem;
size_t mem_size;
size_t window_size;
};
static void *zstd_init(struct squashfs_sb_info *msblk, void *buff)
{
struct workspace *wksp = kmalloc(sizeof(*wksp), GFP_KERNEL);
if (wksp == NULL)
goto failed;
wksp->window_size = max_t(size_t,
msblk->block_size, SQUASHFS_METADATA_SIZE);
wksp->mem_size = ZSTD_DStreamWorkspaceBound(wksp->window_size);
wksp->mem = vmalloc(wksp->mem_size);
if (wksp->mem == NULL)
goto failed;
return wksp;
failed:
ERROR("Failed to allocate zstd workspace\n");
kfree(wksp);
return ERR_PTR(-ENOMEM);
}
static void zstd_free(void *strm)
{
struct workspace *wksp = strm;
if (wksp)
vfree(wksp->mem);
kfree(wksp);
}
static int zstd_uncompress(struct squashfs_sb_info *msblk, void *strm,
struct buffer_head **bh, int b, int offset, int length,
struct squashfs_page_actor *output)
{
struct workspace *wksp = strm;
ZSTD_DStream *stream;
size_t total_out = 0;
size_t zstd_err;
int k = 0;
ZSTD_inBuffer in_buf = { NULL, 0, 0 };
ZSTD_outBuffer out_buf = { NULL, 0, 0 };
stream = ZSTD_initDStream(wksp->window_size, wksp->mem, wksp->mem_size);
if (!stream) {
ERROR("Failed to initialize zstd decompressor\n");
goto out;
}
out_buf.size = PAGE_SIZE;
out_buf.dst = squashfs_first_page(output);
do {
if (in_buf.pos == in_buf.size && k < b) {
int avail = min(length, msblk->devblksize - offset);
length -= avail;
in_buf.src = bh[k]->b_data + offset;
in_buf.size = avail;
in_buf.pos = 0;
offset = 0;
}
if (out_buf.pos == out_buf.size) {
out_buf.dst = squashfs_next_page(output);
if (out_buf.dst == NULL) {
/* Shouldn't run out of pages
* before stream is done.
*/
squashfs_finish_page(output);
goto out;
}
out_buf.pos = 0;
out_buf.size = PAGE_SIZE;
}
total_out -= out_buf.pos;
zstd_err = ZSTD_decompressStream(stream, &out_buf, &in_buf);
total_out += out_buf.pos; /* add the additional data produced */
if (in_buf.pos == in_buf.size && k < b)
put_bh(bh[k++]);
} while (zstd_err != 0 && !ZSTD_isError(zstd_err));
squashfs_finish_page(output);
if (ZSTD_isError(zstd_err)) {
ERROR("zstd decompression error: %d\n",
(int)ZSTD_getErrorCode(zstd_err));
goto out;
}
if (k < b)
goto out;
return (int)total_out;
out:
for (; k < b; k++)
put_bh(bh[k]);
return -EIO;
}
const struct squashfs_decompressor squashfs_zstd_comp_ops = {
.init = zstd_init,
.free = zstd_free,
.decompress = zstd_uncompress,
.id = ZSTD_COMPRESSION,
.name = "zstd",
.supported = 1
};