tjh.dev
Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
1# SPDX-License-Identifier: GPL-2.0-only
2config SQUASHFS
3 tristate "SquashFS 4.0 - Squashed file system support"
4 depends on BLOCK
5 help
6 Saying Y here includes support for SquashFS 4.0 (a Compressed
7 Read-Only File System). Squashfs is a highly compressed read-only
8 filesystem for Linux. It uses zlib, lz4, lzo, xz or zstd compression
9 to compress both files, inodes and directories. Inodes in the system
10 are very small and all blocks are packed to minimise data overhead.
11 Block sizes greater than 4K are supported up to a maximum of 1 Mbytes
12 (default block size 128K). SquashFS 4.0 supports 64 bit filesystems
13 and files (larger than 4GB), full uid/gid information, hard links and
14 timestamps.
15
16 Squashfs is intended for general read-only filesystem use, for
17 archival use (i.e. in cases where a .tar.gz file may be used), and in
18 embedded systems where low overhead is needed. Further information
19 and tools are available from github.com/plougher/squashfs-tools.
20
21 If you want to compile this as a module ( = code which can be
22 inserted in and removed from the running kernel whenever you want),
23 say M here. The module will be called squashfs. Note that the root
24 file system (the one containing the directory /) cannot be compiled
25 as a module.
26
27 If unsure, say N.
28
29choice
30 prompt "File decompression options"
31 depends on SQUASHFS
32 help
33 Squashfs now supports two options for decompressing file
34 data. Traditionally Squashfs has decompressed into an
35 intermediate buffer and then memcopied it into the page cache.
36 Squashfs now supports the ability to decompress directly into
37 the page cache.
38
39 If unsure, select "Decompress file data into an intermediate buffer"
40
41config SQUASHFS_FILE_CACHE
42 bool "Decompress file data into an intermediate buffer"
43 help
44 Decompress file data into an intermediate buffer and then
45 memcopy it into the page cache.
46
47config SQUASHFS_FILE_DIRECT
48 bool "Decompress files directly into the page cache"
49 help
50 Directly decompress file data into the page cache.
51 Doing so can significantly improve performance because
52 it eliminates a memcpy and it also removes the lock contention
53 on the single buffer.
54
55endchoice
56
57config SQUASHFS_DECOMP_SINGLE
58 depends on SQUASHFS
59 def_bool n
60
61config SQUASHFS_DECOMP_MULTI
62 depends on SQUASHFS
63 def_bool n
64
65config SQUASHFS_DECOMP_MULTI_PERCPU
66 depends on SQUASHFS
67 def_bool n
68
69config SQUASHFS_CHOICE_DECOMP_BY_MOUNT
70 bool "Select the parallel decompression mode during mount"
71 depends on SQUASHFS
72 default n
73 select SQUASHFS_DECOMP_SINGLE
74 select SQUASHFS_DECOMP_MULTI
75 select SQUASHFS_DECOMP_MULTI_PERCPU
76 select SQUASHFS_MOUNT_DECOMP_THREADS
77 help
78 Compile all parallel decompression modes and specify the
79 decompression mode by setting "threads=" during mount.
80 default Decompressor parallelisation is SQUASHFS_DECOMP_SINGLE
81
82choice
83 prompt "Select decompression parallel mode at compile time"
84 depends on SQUASHFS
85 depends on !SQUASHFS_CHOICE_DECOMP_BY_MOUNT
86 help
87 Squashfs now supports three parallelisation options for
88 decompression. Each one exhibits various trade-offs between
89 decompression performance and CPU and memory usage.
90
91 If in doubt, select "Single threaded compression"
92
93config SQUASHFS_COMPILE_DECOMP_SINGLE
94 bool "Single threaded compression"
95 select SQUASHFS_DECOMP_SINGLE
96 help
97 Traditionally Squashfs has used single-threaded decompression.
98 Only one block (data or metadata) can be decompressed at any
99 one time. This limits CPU and memory usage to a minimum.
100
101config SQUASHFS_COMPILE_DECOMP_MULTI
102 bool "Use multiple decompressors for parallel I/O"
103 select SQUASHFS_DECOMP_MULTI
104 help
105 By default Squashfs uses a single decompressor but it gives
106 poor performance on parallel I/O workloads when using multiple CPU
107 machines due to waiting on decompressor availability.
108
109 If you have a parallel I/O workload and your system has enough memory,
110 using this option may improve overall I/O performance.
111
112 This decompressor implementation uses up to two parallel
113 decompressors per core. It dynamically allocates decompressors
114 on a demand basis.
115
116config SQUASHFS_COMPILE_DECOMP_MULTI_PERCPU
117 bool "Use percpu multiple decompressors for parallel I/O"
118 select SQUASHFS_DECOMP_MULTI_PERCPU
119 help
120 By default Squashfs uses a single decompressor but it gives
121 poor performance on parallel I/O workloads when using multiple CPU
122 machines due to waiting on decompressor availability.
123
124 This decompressor implementation uses a maximum of one
125 decompressor per core. It uses percpu variables to ensure
126 decompression is load-balanced across the cores.
127endchoice
128
129config SQUASHFS_MOUNT_DECOMP_THREADS
130 bool "Add the mount parameter 'threads=' for squashfs"
131 depends on SQUASHFS
132 depends on SQUASHFS_DECOMP_MULTI
133 default n
134 help
135 Use threads= to set the decompression parallel mode and the number of threads.
136 If SQUASHFS_CHOICE_DECOMP_BY_MOUNT=y
137 threads=<single|multi|percpu|1|2|3|...>
138 else
139 threads=<2|3|...>
140 The upper limit is num_online_cpus() * 2.
141
142config SQUASHFS_XATTR
143 bool "Squashfs XATTR support"
144 depends on SQUASHFS
145 help
146 Saying Y here includes support for extended attributes (xattrs).
147 Xattrs are name:value pairs associated with inodes by
148 the kernel or by users (see the attr(5) manual page).
149
150 If unsure, say N.
151
152config SQUASHFS_COMP_CACHE_FULL
153 bool "Enable full caching of compressed blocks"
154 depends on SQUASHFS
155 default n
156 help
157 This option enables caching of all compressed blocks, Without caching,
158 repeated reads of the same files trigger excessive disk I/O, significantly
159 reducinng performance in workloads like fio-based benchmarks.
160
161 For example, fio tests (iodepth=1, numjobs=1, ioengine=psync) show:
162 With caching: IOPS=2223, BW=278MiB/s (291MB/s)
163 Without caching: IOPS=815, BW=102MiB/s (107MB/s)
164
165 Enabling this option restores performance to pre-regression levels by
166 caching all compressed blocks in the page cache, reducing disk I/O for
167 repeated reads. However, this increases memory usage, which may be a
168 concern in memory-constrained environments.
169
170 Enable this option if your workload involves frequent repeated reads and
171 memory usage is not a limiting factor. If unsure, say N.
172
173config SQUASHFS_ZLIB
174 bool "Include support for ZLIB compressed file systems"
175 depends on SQUASHFS
176 select ZLIB_INFLATE
177 default y
178 help
179 ZLIB compression is the standard compression used by Squashfs
180 file systems. It offers a good trade-off between compression
181 achieved and the amount of CPU time and memory necessary to
182 compress and decompress.
183
184 If unsure, say Y.
185
186config SQUASHFS_LZ4
187 bool "Include support for LZ4 compressed file systems"
188 depends on SQUASHFS
189 select LZ4_DECOMPRESS
190 help
191 Saying Y here includes support for reading Squashfs file systems
192 compressed with LZ4 compression. LZ4 compression is mainly
193 aimed at embedded systems with slower CPUs where the overheads
194 of zlib are too high.
195
196 LZ4 is not the standard compression used in Squashfs and so most
197 file systems will be readable without selecting this option.
198
199 If unsure, say N.
200
201config SQUASHFS_LZO
202 bool "Include support for LZO compressed file systems"
203 depends on SQUASHFS
204 select LZO_DECOMPRESS
205 help
206 Saying Y here includes support for reading Squashfs file systems
207 compressed with LZO compression. LZO compression is mainly
208 aimed at embedded systems with slower CPUs where the overheads
209 of zlib are too high.
210
211 LZO is not the standard compression used in Squashfs and so most
212 file systems will be readable without selecting this option.
213
214 If unsure, say N.
215
216config SQUASHFS_XZ
217 bool "Include support for XZ compressed file systems"
218 depends on SQUASHFS
219 select XZ_DEC
220 help
221 Saying Y here includes support for reading Squashfs file systems
222 compressed with XZ compression. XZ gives better compression than
223 the default zlib compression, at the expense of greater CPU and
224 memory overhead.
225
226 XZ is not the standard compression used in Squashfs and so most
227 file systems will be readable without selecting this option.
228
229 If unsure, say N.
230
231config SQUASHFS_ZSTD
232 bool "Include support for ZSTD compressed file systems"
233 depends on SQUASHFS
234 select ZSTD_DECOMPRESS
235 help
236 Saying Y here includes support for reading Squashfs file systems
237 compressed with ZSTD compression. ZSTD gives better compression than
238 the default ZLIB compression, while using less CPU.
239
240 ZSTD is not the standard compression used in Squashfs and so most
241 file systems will be readable without selecting this option.
242
243 If unsure, say N.
244
245config SQUASHFS_4K_DEVBLK_SIZE
246 bool "Use 4K device block size?"
247 depends on SQUASHFS
248 help
249 By default Squashfs sets the dev block size (sb_min_blocksize)
250 to 1K or the smallest block size supported by the block device
251 (if larger). This, because blocks are packed together and
252 unaligned in Squashfs, should reduce latency.
253
254 This, however, gives poor performance on MTD NAND devices where
255 the optimal I/O size is 4K (even though the devices can support
256 smaller block sizes).
257
258 Using a 4K device block size may also improve overall I/O
259 performance for some file access patterns (e.g. sequential
260 accesses of files in filesystem order) on all media.
261
262 Setting this option will force Squashfs to use a 4K device block
263 size by default.
264
265 If unsure, say N.
266
267config SQUASHFS_EMBEDDED
268 bool "Additional option for memory-constrained systems"
269 depends on SQUASHFS
270 help
271 Saying Y here allows you to specify cache size.
272
273 If unsure, say N.
274
275config SQUASHFS_FRAGMENT_CACHE_SIZE
276 int "Number of fragments cached" if SQUASHFS_EMBEDDED
277 depends on SQUASHFS
278 default "3"
279 help
280 By default SquashFS caches the last 3 fragments read from
281 the filesystem. Increasing this amount may mean SquashFS
282 has to re-read fragments less often from disk, at the expense
283 of extra system memory. Decreasing this amount will mean
284 SquashFS uses less memory at the expense of extra reads from disk.
285
286 Note there must be at least one cached fragment. Anything
287 much more than three will probably not make much difference.