| config SQUASHFS |
| tristate "SquashFS 4.0 - Squashed file system support" |
| depends on BLOCK |
| help |
| Saying Y here includes support for SquashFS 4.0 (a Compressed |
| Read-Only File System). Squashfs is a highly compressed read-only |
| filesystem for Linux. It uses zlib, lzo or xz compression to |
| compress both files, inodes and directories. Inodes in the system |
| are very small and all blocks are packed to minimise data overhead. |
| Block sizes greater than 4K are supported up to a maximum of 1 Mbytes |
| (default block size 128K). SquashFS 4.0 supports 64 bit filesystems |
| and files (larger than 4GB), full uid/gid information, hard links and |
| timestamps. |
| |
| Squashfs is intended for general read-only filesystem use, for |
| archival use (i.e. in cases where a .tar.gz file may be used), and in |
| embedded systems where low overhead is needed. Further information |
| and tools are available from http://squashfs.sourceforge.net. |
| |
| If you want to compile this as a module ( = code which can be |
| inserted in and removed from the running kernel whenever you want), |
| say M here. The module will be called squashfs. Note that the root |
| file system (the one containing the directory /) cannot be compiled |
| as a module. |
| |
| If unsure, say N. |
| |
| choice |
| prompt "File decompression options" |
| depends on SQUASHFS |
| help |
| Squashfs now supports two options for decompressing file |
| data. Traditionally Squashfs has decompressed into an |
| intermediate buffer and then memcopied it into the page cache. |
| Squashfs now supports the ability to decompress directly into |
| the page cache. |
| |
| If unsure, select "Decompress file data into an intermediate buffer" |
| |
| config SQUASHFS_FILE_CACHE |
| bool "Decompress file data into an intermediate buffer" |
| help |
| Decompress file data into an intermediate buffer and then |
| memcopy it into the page cache. |
| |
| config SQUASHFS_FILE_DIRECT |
| bool "Decompress files directly into the page cache" |
| help |
| Directly decompress file data into the page cache. |
| Doing so can significantly improve performance because |
| it eliminates a memcpy and it also removes the lock contention |
| on the single buffer. |
| |
| endchoice |
| |
| choice |
| prompt "Decompressor parallelisation options" |
| depends on SQUASHFS |
| help |
| Squashfs now supports three parallelisation options for |
| decompression. Each one exhibits various trade-offs between |
| decompression performance and CPU and memory usage. |
| |
| If in doubt, select "Single threaded compression" |
| |
| config SQUASHFS_DECOMP_SINGLE |
| bool "Single threaded compression" |
| help |
| Traditionally Squashfs has used single-threaded decompression. |
| Only one block (data or metadata) can be decompressed at any |
| one time. This limits CPU and memory usage to a minimum. |
| |
| config SQUASHFS_DECOMP_MULTI |
| bool "Use multiple decompressors for parallel I/O" |
| help |
| By default Squashfs uses a single decompressor but it gives |
| poor performance on parallel I/O workloads when using multiple CPU |
| machines due to waiting on decompressor availability. |
| |
| If you have a parallel I/O workload and your system has enough memory, |
| using this option may improve overall I/O performance. |
| |
| This decompressor implementation uses up to two parallel |
| decompressors per core. It dynamically allocates decompressors |
| on a demand basis. |
| |
| config SQUASHFS_DECOMP_MULTI_PERCPU |
| bool "Use percpu multiple decompressors for parallel I/O" |
| help |
| By default Squashfs uses a single decompressor but it gives |
| poor performance on parallel I/O workloads when using multiple CPU |
| machines due to waiting on decompressor availability. |
| |
| This decompressor implementation uses a maximum of one |
| decompressor per core. It uses percpu variables to ensure |
| decompression is load-balanced across the cores. |
| |
| endchoice |
| |
| config SQUASHFS_XATTR |
| bool "Squashfs XATTR support" |
| depends on SQUASHFS |
| help |
| Saying Y here includes support for extended attributes (xattrs). |
| Xattrs are name:value pairs associated with inodes by |
| the kernel or by users (see the attr(5) manual page). |
| |
| If unsure, say N. |
| |
| config SQUASHFS_ZLIB |
| bool "Include support for ZLIB compressed file systems" |
| depends on SQUASHFS |
| select ZLIB_INFLATE |
| default y |
| help |
| ZLIB compression is the standard compression used by Squashfs |
| file systems. It offers a good trade-off between compression |
| achieved and the amount of CPU time and memory necessary to |
| compress and decompress. |
| |
| If unsure, say Y. |
| |
| config SQUASHFS_LZ4 |
| bool "Include support for LZ4 compressed file systems" |
| depends on SQUASHFS |
| select LZ4_DECOMPRESS |
| help |
| Saying Y here includes support for reading Squashfs file systems |
| compressed with LZ4 compression. LZ4 compression is mainly |
| aimed at embedded systems with slower CPUs where the overheads |
| of zlib are too high. |
| |
| LZ4 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_LZO |
| bool "Include support for LZO compressed file systems" |
| depends on SQUASHFS |
| select LZO_DECOMPRESS |
| help |
| Saying Y here includes support for reading Squashfs file systems |
| compressed with LZO compression. LZO compression is mainly |
| aimed at embedded systems with slower CPUs where the overheads |
| of zlib are too high. |
| |
| LZO 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_XZ |
| bool "Include support for XZ compressed file systems" |
| depends on SQUASHFS |
| select XZ_DEC |
| help |
| Saying Y here includes support for reading Squashfs file systems |
| compressed with XZ compression. XZ gives better compression than |
| the default zlib compression, at the expense of greater CPU and |
| memory overhead. |
| |
| XZ 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 |
| help |
| By default Squashfs sets the dev block size (sb_min_blocksize) |
| to 1K or the smallest block size supported by the block device |
| (if larger). This, because blocks are packed together and |
| unaligned in Squashfs, should reduce latency. |
| |
| This, however, gives poor performance on MTD NAND devices where |
| the optimal I/O size is 4K (even though the devices can support |
| smaller block sizes). |
| |
| Using a 4K device block size may also improve overall I/O |
| performance for some file access patterns (e.g. sequential |
| accesses of files in filesystem order) on all media. |
| |
| Setting this option will force Squashfs to use a 4K device block |
| size by default. |
| |
| If unsure, say N. |
| |
| config SQUASHFS_EMBEDDED |
| bool "Additional option for memory-constrained systems" |
| depends on SQUASHFS |
| help |
| Saying Y here allows you to specify cache size. |
| |
| If unsure, say N. |
| |
| config SQUASHFS_FRAGMENT_CACHE_SIZE |
| int "Number of fragments cached" if SQUASHFS_EMBEDDED |
| depends on SQUASHFS |
| default "3" |
| help |
| By default SquashFS caches the last 3 fragments read from |
| the filesystem. Increasing this amount may mean SquashFS |
| has to re-read fragments less often from disk, at the expense |
| of extra system memory. Decreasing this amount will mean |
| SquashFS uses less memory at the expense of extra reads from disk. |
| |
| Note there must be at least one cached fragment. Anything |
| much more than three will probably not make much difference. |
