VSwap testing

This article describes how to test VSwap functionality

[originally written by xemul@]

We need the following set of atomic tests

• RAM limit works
• SWAP limit works
• OOM killer works
• Pages sent to swap can be read back again
• No real swapout starts when there's enough RAM on the node
• No leaks happen after container stop

To do this the following set of atomic tests is required: 1) RAM limit works

• Start container with unlimited RAM and SWAP.
• Note the physpages.held value
• Set RAM = physpages.held + X
• Run memeater, that will map and touch RAM pages
• _Before_ memeater exits check, that physpages.held didn't grow above the .limit

2) SWAP limit works

• Start container with unlimited RAM and SWAP.
• Note the physpages.held value
• Set RAM = physpages.held + X
• Set SWAP = Y
• Run memeater, that will map and touch RAM + SWAP pages
• Check that none of physpages.held and swappages.held grew above the .limit (memeater _may_ be killed during this test)

3) OOM killer works

• Start two containers with unlimited RAM and SWAP
• Set RAM and SWAP for both like in previous examples
• Run memeater in one of them, that consumes infinite amount of RAM.
• Check, that memeater is killed in the 1st container
• Check, that no tasks in the 2nd one are killed

(the above three can probably be made of vzt-slm test) 4) Pages sent to swap can be read back again

• Start container with unlimited RAM and SWAP.
• Note the physpages.held value
• Set RAM = physpages.held + X
• Run memeater, that will map and write to 2xRAM pages
• Check, that swappages.held is not zero
• Make memeater read the whole memory again and check that the values written are preserved

5) No real swapout starts when there's enough RAM on the node

• Take a node with non-zero swap partition
• Start a container with unlimited RAM and SWAP
• Note the physpages.held value
• Check that real swap is not used
• Set RAM = physpages.held + X
• Run memeater, that will eat 2xRAM pages
• Check, that memeater is not dead
• Before memeater exits check, that swappages.held is not zero
• Check that real swap is still not used

6) No leaks happen after container stop. This will be done using kmemleak - see PSBM-34183