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# SPDX-License-Identifier: GPL-2.0
config ZRAM
tristate "Compressed RAM block device support"
depends on BLOCK && SYSFS && MMU
depends on CRYPTO_LZO || CRYPTO_ZSTD || CRYPTO_LZ4 || CRYPTO_LZ4HC || CRYPTO_842
select ZSMALLOC
help
Creates virtual block devices called /dev/zramX (X = 0, 1, ...).
Pages written to these disks are compressed and stored in memory
itself. These disks allow very fast I/O and compression provides
good amounts of memory savings.
It has several use cases, for example: /tmp storage, use as swap
disks and maybe many more.
See Documentation/admin-guide/blockdev/zram.rst for more information.
choice
prompt "Default zram compressor"
default ZRAM_DEF_COMP_LZORLE
depends on ZRAM
config ZRAM_DEF_COMP_LZORLE
bool "lzo-rle"
depends on CRYPTO_LZO
config ZRAM_DEF_COMP_ZSTD
bool "zstd"
depends on CRYPTO_ZSTD
config ZRAM_DEF_COMP_LZ4
bool "lz4"
depends on CRYPTO_LZ4
config ZRAM_DEF_COMP_LZO
bool "lzo"
depends on CRYPTO_LZO
config ZRAM_DEF_COMP_LZ4HC
bool "lz4hc"
depends on CRYPTO_LZ4HC
config ZRAM_DEF_COMP_842
bool "842"
depends on CRYPTO_842
endchoice
config ZRAM_DEF_COMP
string
default "lzo-rle" if ZRAM_DEF_COMP_LZORLE
default "zstd" if ZRAM_DEF_COMP_ZSTD
default "lz4" if ZRAM_DEF_COMP_LZ4
default "lzo" if ZRAM_DEF_COMP_LZO
default "lz4hc" if ZRAM_DEF_COMP_LZ4HC
default "842" if ZRAM_DEF_COMP_842
config ZRAM_WRITEBACK
bool "Write back incompressible or idle page to backing device"
depends on ZRAM
help
This lets zram entries (incompressible or idle pages) be written
back to a backing device, helping save memory.
For this feature, admin should set up backing device via
/sys/block/zramX/backing_dev.
With /sys/block/zramX/{idle,writeback}, application could ask
idle page's writeback to the backing device to save in memory.
See Documentation/admin-guide/blockdev/zram.rst for more information.
config ZRAM_TRACK_ENTRY_ACTIME
bool "Track access time of zram entries"
depends on ZRAM
help
With this feature zram tracks access time of every stored
entry (page), which can be used for a more fine grained IDLE
pages writeback.
config ZRAM_MEMORY_TRACKING
bool "Track zRam block status"
depends on ZRAM && DEBUG_FS
select ZRAM_TRACK_ENTRY_ACTIME
help
With this feature, admin can track the state of allocated blocks
of zRAM. Admin could see the information via
/sys/kernel/debug/zram/zramX/block_state.
See Documentation/admin-guide/blockdev/zram.rst for more information.
config ZRAM_MULTI_COMP
bool "Enable multiple compression streams"
depends on ZRAM
help
This will enable multi-compression streams, so that ZRAM can
re-compress pages using a potentially slower but more effective
compression algorithm. Note, that IDLE page recompression
requires ZRAM_TRACK_ENTRY_ACTIME.
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