admin-guide/blockdev/zram.rst

10 in memory itself. These disks allow very fast I/O and compression provides
76 2) Select compression algorithm
80 currently selected (shown in square brackets) compression algorithms,
81 or change the selected compression algorithm (once the device is initialised
82 there is no way to change compression algorithm).
86 	#show supported compression algorithms
90 	#select lzo compression algorithm
93 For the time being, the `comp_algorithm` content shows only compression
96 3) Set compression algorithm parameters: Optional
103 For example, several compression algorithms support `level` parameter.
104 In addition, certain compression algorithms support pre-trained dictionaries,
106 compression algorithm to use external pre-trained dictionary, pass full
116 	#pass path to pre-trained zstd dictionary and compression level
122 algorithms `level` controls the compression level (the higher the value the
123 better the compression ratio, it even can take negatives values for some
125 the value the lower the compression ratio).
144 since we expect a 2:1 compression ratio. Note that zram uses about 0.1% of the
217 comp_algorithm    	RW	show and change the compression algorithm
218 algorithm_params	WO	setup compression algorithm parameters
444 (secondary) compression algorithms. The basic idea is that alternative
445 compression algorithm can provide better compression ratio at a price of
446 (potentially) slower compression/decompression speeds. Alternative compression
452 With CONFIG_ZRAM_MULTI_COMP, zram supports up to 4 compression algorithms:
454 in "3) Select compression algorithm", secondary algorithms are configured
464 Alternative compression algorithms are sorted by priority. In the example
466 of 1, while lz4hc is configured as a compression algorithm with priority 2.
467 Alternative compression algorithm's priority is provided during algorithms
500 It is also possible to limit the number of pages zram re-compression will
505 During re-compression for every page, that matches re-compression criteria,
506 ZRAM iterates the list of registered alternative compression algorithms in
507 order of their priorities. ZRAM stops either when re-compression was
509 and matches re-compression criteria (e.g. size threshold) or when there are
514 This re-compression behaviour, when it iterates through the list of
515 registered compression algorithms, increases our chances of finding the
559 		recompressed page (secondary compression algorithm)