81 lines
3.0 KiB
ReStructuredText
81 lines
3.0 KiB
ReStructuredText
.. _swap_numa:
|
|
|
|
===========================================
|
|
Automatically bind swap device to numa node
|
|
===========================================
|
|
|
|
If the system has more than one swap device and swap device has the node
|
|
information, we can make use of this information to decide which swap
|
|
device to use in get_swap_pages() to get better performance.
|
|
|
|
|
|
How to use this feature
|
|
=======================
|
|
|
|
Swap device has priority and that decides the order of it to be used. To make
|
|
use of automatically binding, there is no need to manipulate priority settings
|
|
for swap devices. e.g. on a 2 node machine, assume 2 swap devices swapA and
|
|
swapB, with swapA attached to node 0 and swapB attached to node 1, are going
|
|
to be swapped on. Simply swapping them on by doing::
|
|
|
|
# swapon /dev/swapA
|
|
# swapon /dev/swapB
|
|
|
|
Then node 0 will use the two swap devices in the order of swapA then swapB and
|
|
node 1 will use the two swap devices in the order of swapB then swapA. Note
|
|
that the order of them being swapped on doesn't matter.
|
|
|
|
A more complex example on a 4 node machine. Assume 6 swap devices are going to
|
|
be swapped on: swapA and swapB are attached to node 0, swapC is attached to
|
|
node 1, swapD and swapE are attached to node 2 and swapF is attached to node3.
|
|
The way to swap them on is the same as above::
|
|
|
|
# swapon /dev/swapA
|
|
# swapon /dev/swapB
|
|
# swapon /dev/swapC
|
|
# swapon /dev/swapD
|
|
# swapon /dev/swapE
|
|
# swapon /dev/swapF
|
|
|
|
Then node 0 will use them in the order of::
|
|
|
|
swapA/swapB -> swapC -> swapD -> swapE -> swapF
|
|
|
|
swapA and swapB will be used in a round robin mode before any other swap device.
|
|
|
|
node 1 will use them in the order of::
|
|
|
|
swapC -> swapA -> swapB -> swapD -> swapE -> swapF
|
|
|
|
node 2 will use them in the order of::
|
|
|
|
swapD/swapE -> swapA -> swapB -> swapC -> swapF
|
|
|
|
Similaly, swapD and swapE will be used in a round robin mode before any
|
|
other swap devices.
|
|
|
|
node 3 will use them in the order of::
|
|
|
|
swapF -> swapA -> swapB -> swapC -> swapD -> swapE
|
|
|
|
|
|
Implementation details
|
|
======================
|
|
|
|
The current code uses a priority based list, swap_avail_list, to decide
|
|
which swap device to use and if multiple swap devices share the same
|
|
priority, they are used round robin. This change here replaces the single
|
|
global swap_avail_list with a per-numa-node list, i.e. for each numa node,
|
|
it sees its own priority based list of available swap devices. Swap
|
|
device's priority can be promoted on its matching node's swap_avail_list.
|
|
|
|
The current swap device's priority is set as: user can set a >=0 value,
|
|
or the system will pick one starting from -1 then downwards. The priority
|
|
value in the swap_avail_list is the negated value of the swap device's
|
|
due to plist being sorted from low to high. The new policy doesn't change
|
|
the semantics for priority >=0 cases, the previous starting from -1 then
|
|
downwards now becomes starting from -2 then downwards and -1 is reserved
|
|
as the promoted value. So if multiple swap devices are attached to the same
|
|
node, they will all be promoted to priority -1 on that node's plist and will
|
|
be used round robin before any other swap devices.
|