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Diffstat (limited to 'Documentation/vm/swap_numa.rst')
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diff --git a/Documentation/vm/swap_numa.rst b/Documentation/vm/swap_numa.rst deleted file mode 100644 index e0466f2db8fa..000000000000 --- a/Documentation/vm/swap_numa.rst +++ /dev/null @@ -1,80 +0,0 @@ -.. _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. |