what's cooking in zram for 4.2

From: Sergey Senozhatsky
Date: Wed Aug 12 2015 - 20:58:43 EST

Hello Karel,

... planned to write this earlier.

zram will see some user-space visible improvements in 4.2 we'd love
to let you know about -- on-demand device creation/removal.

For that purpose we introduce zram control sysfs class, which has two
sysfs attrs:
- hot_add -- add a new zram device
- hot_remove -- remove a specific (device_id) zram device

-- hot_add sysfs attr is read-only and has only automatic device id
assignment mode. Read operation performed on this attr creates a
new zram device and returns back its device_id (or error (ret < 0)).

Usage example:
# add a new zram device
cat /sys/class/zram-control/hot_add

an example of returning error code (-ENOMEM in this case)

cat /sys/class/zram-control/hot_add
cat: /sys/class/zram-control/hot_add: Cannot allocate memory

-- hot_remove is write only and requires a valid zram device_id as
its input parameter:

# remove a specific zram device
echo 4 > /sys/class/zram-control/hot_remove

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