a2468cc9bf
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. 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 patch changes the previous single global swap_avail_list into 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. Take 4-node EX machine as an example, suppose 4 swap devices are available, each sit on a different node: swapA on node 0 swapB on node 1 swapC on node 2 swapD on node 3 After they are all swapped on in the sequence of ABCD. Current behaviour: their priorities will be: swapA: -1 swapB: -2 swapC: -3 swapD: -4 And their position in the global swap_avail_list will be: swapA -> swapB -> swapC -> swapD prio:1 prio:2 prio:3 prio:4 New behaviour: their priorities will be(note that -1 is skipped): swapA: -2 swapB: -3 swapC: -4 swapD: -5 And their positions in the 4 swap_avail_lists[nid] will be: swap_avail_lists[0]: /* node 0's available swap device list */ swapA -> swapB -> swapC -> swapD prio:1 prio:3 prio:4 prio:5 swap_avali_lists[1]: /* node 1's available swap device list */ swapB -> swapA -> swapC -> swapD prio:1 prio:2 prio:4 prio:5 swap_avail_lists[2]: /* node 2's available swap device list */ swapC -> swapA -> swapB -> swapD prio:1 prio:2 prio:3 prio:5 swap_avail_lists[3]: /* node 3's available swap device list */ swapD -> swapA -> swapB -> swapC prio:1 prio:2 prio:3 prio:4 To see the effect of the patch, a test that starts N process, each mmap a region of anonymous memory and then continually write to it at random position to trigger both swap in and out is used. On a 2 node Skylake EP machine with 64GiB memory, two 170GB SSD drives are used as swap devices with each attached to a different node, the result is: runtime=30m/processes=32/total test size=128G/each process mmap region=4G kernel throughput vanilla 13306 auto-binding 15169 +14% runtime=30m/processes=64/total test size=128G/each process mmap region=2G kernel throughput vanilla 11885 auto-binding 14879 +25% [aaron.lu@intel.com: v2] Link: http://lkml.kernel.org/r/20170814053130.GD2369@aaronlu.sh.intel.com Link: http://lkml.kernel.org/r/20170816024439.GA10925@aaronlu.sh.intel.com [akpm@linux-foundation.org: use kmalloc_array()] Link: http://lkml.kernel.org/r/20170814053130.GD2369@aaronlu.sh.intel.com Link: http://lkml.kernel.org/r/20170816024439.GA10925@aaronlu.sh.intel.com Signed-off-by: Aaron Lu <aaron.lu@intel.com> Cc: "Chen, Tim C" <tim.c.chen@intel.com> Cc: Huang Ying <ying.huang@intel.com> Cc: Andi Kleen <andi@firstfloor.org> Cc: Michal Hocko <mhocko@suse.com> Cc: Minchan Kim <minchan@kernel.org> Cc: Hugh Dickins <hughd@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
69 lines
2.9 KiB
Text
69 lines
2.9 KiB
Text
Automatically bind swap device to numa node
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If the system has more than one swap device and swap device has the node
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information, we can make use of this information to decide which swap
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device to use in get_swap_pages() to get better performance.
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How to use this feature
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-----------------------
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Swap device has priority and that decides the order of it to be used. To make
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use of automatically binding, there is no need to manipulate priority settings
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for swap devices. e.g. on a 2 node machine, assume 2 swap devices swapA and
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swapB, with swapA attached to node 0 and swapB attached to node 1, are going
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to be swapped on. Simply swapping them on by doing:
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# swapon /dev/swapA
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# swapon /dev/swapB
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Then node 0 will use the two swap devices in the order of swapA then swapB and
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node 1 will use the two swap devices in the order of swapB then swapA. Note
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that the order of them being swapped on doesn't matter.
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A more complex example on a 4 node machine. Assume 6 swap devices are going to
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be swapped on: swapA and swapB are attached to node 0, swapC is attached to
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node 1, swapD and swapE are attached to node 2 and swapF is attached to node3.
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The way to swap them on is the same as above:
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# swapon /dev/swapA
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# swapon /dev/swapB
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# swapon /dev/swapC
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# swapon /dev/swapD
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# swapon /dev/swapE
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# swapon /dev/swapF
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Then node 0 will use them in the order of:
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swapA/swapB -> swapC -> swapD -> swapE -> swapF
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swapA and swapB will be used in a round robin mode before any other swap device.
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node 1 will use them in the order of:
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swapC -> swapA -> swapB -> swapD -> swapE -> swapF
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node 2 will use them in the order of:
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swapD/swapE -> swapA -> swapB -> swapC -> swapF
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Similaly, swapD and swapE will be used in a round robin mode before any
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other swap devices.
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node 3 will use them in the order of:
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swapF -> swapA -> swapB -> swapC -> swapD -> swapE
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Implementation details
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----------------------
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The current code uses a priority based list, swap_avail_list, to decide
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which swap device to use and if multiple swap devices share the same
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priority, they are used round robin. This change here replaces the single
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global swap_avail_list with a per-numa-node list, i.e. for each numa node,
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it sees its own priority based list of available swap devices. Swap
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device's priority can be promoted on its matching node's swap_avail_list.
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The current swap device's priority is set as: user can set a >=0 value,
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or the system will pick one starting from -1 then downwards. The priority
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value in the swap_avail_list is the negated value of the swap device's
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due to plist being sorted from low to high. The new policy doesn't change
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the semantics for priority >=0 cases, the previous starting from -1 then
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downwards now becomes starting from -2 then downwards and -1 is reserved
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as the promoted value. So if multiple swap devices are attached to the same
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node, they will all be promoted to priority -1 on that node's plist and will
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be used round robin before any other swap devices.
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