admin-guide/blockdev/zram.rst

2 zram: Compressed RAM-based block devices
8 The zram module creates RAM-based block devices named /dev/zram<id>
20 There are several ways to configure and manage zram device(-s):
23 b) using zramctl utility, provided by util-linux (util-linux@vger.kernel.org).
28 In order to get a better idea about zramctl please consult util-linux
29 documentation, zramctl man-page or `zramctl --help`. Please be informed
30 that zram maintainers do not develop/maintain util-linux or zramctl, should
31 you have any questions please contact util-linux@vger.kernel.org
45 -EBUSY	  an attempt to modify an attribute that cannot be changed once
47 -ENOMEM	  zram was not able to allocate enough memory to fulfil your
49 -EINVAL	  invalid input has been provided.
56 	if [ $? -ne 0 ]; then
58 	fi
72 pre-created. Default: 1.
78 allocate multiple compression streams - one per online CPU - thus
81 become offline. There is no single-compression-stream mode anymore,
168 zram provides a control interface, which enables dynamic (on-demand) device
177 	cat /sys/class/zram-control/hot_add
183 	echo X > /sys/class/zram-control/hot_remove
188 Per-device statistics are exported as various nodes under /sys/block/zram<id>/
191 please read Documentation/ABI/testing/sysfs-block-zram.
232  invalid_io       The number of non-page-size-aligned I/O requests
310 ---------
378 If admin wants to limit writeback as per-day 400M, they could do it
410 -------------
418 recompression - pages that are cold and sit in the memory can be recompressed
430 	#1: lzo lzo-rle lz4 lz4hc [zstd]
431 	#2: lzo lzo-rle lz4 [lz4hc] zstd
459 The number of idle pages can be significant, so user-space can pass a size
471 During re-compression for every page, that matches re-compression criteria,
473 order of their priorities. ZRAM stops either when re-compression was
474 successful (re-compressed object is smaller in size than the original one)
475 and matches re-compression criteria (e.g. size threshold) or when there are
477 successfully re-compressed the page such a page is marked as incompressible,
478 so ZRAM will not attempt to re-compress it in the future.
480 This re-compression behaviour, when it iterates through the list of
502 	  302    63.806919 ..hi..
504 	  304   146.781902 ..hi.n