admin-guide/blockdev/zram.rst

10 in memory itself. These disks allow very fast I/O and compression provides
74 2) Set max number of compression streams
78 allocate multiple compression streams - one per online CPU - thus
79 allowing several concurrent compression operations. The number of
80 allocated compression streams goes down when some of the CPUs
81 become offline. There is no single-compression-stream mode anymore,
88 3) Select compression algorithm
92 currently selected (shown in square brackets) compression algorithms,
93 or change the selected compression algorithm (once the device is initialised
94 there is no way to change compression algorithm).
98 	#show supported compression algorithms
102 	#select lzo compression algorithm
106 show every compression algorithm supported by the kernel. We keep this
108 a new device with a compression algorithm that is not listed in
113 custom crypto compression modules (implementing S/W or H/W compression).
132 since we expect a 2:1 compression ratio. Note that zram uses about 0.1% of the
207 comp_algorithm    	RW	show and change the compression algorithm
413 (secondary) compression algorithms. The basic idea is that alternative
414 compression algorithm can provide better compression ratio at a price of
415 (potentially) slower compression/decompression speeds. Alternative compression
421 With CONFIG_ZRAM_MULTI_COMP, zram supports up to 4 compression algorithms:
423 in "3) Select compression algorithm", secondary algorithms are configured
433 Alternative compression algorithms are sorted by priority. In the example
435 of 1, while lz4hc is configured as a compression algorithm with priority 2.
436 Alternative compression algorithm's priority is provided during algorithms
471 During re-compression for every page, that matches re-compression criteria,
472 ZRAM iterates the list of registered alternative compression algorithms in
473 order of their priorities. ZRAM stops either when re-compression was
475 and matches re-compression criteria (e.g. size threshold) or when there are
480 This re-compression behaviour, when it iterates through the list of
481 registered compression algorithms, increases our chances of finding the
522 		recompressed page (secondary compression algorithm)