[LTP] [PATCH] memcg_control_test: Disable swapping in test cgroup

[T.J. Mercier]

On Thu, Mar 27, 2025 at 6:36 AM Michal Koutný <mkoutny@suse.com> wrote:
>
> Hello.
>
> On Wed, Mar 26, 2025 at 10:35:32PM +0000, "T.J. Mercier" <tjmercier@google.com> wrote:
> > memcg_control_test_1 sets both a memory limit and a memsw/swap limit to
> > a single page, and then asks mem_process to allocate 2 pages in an
> > attempt to cause a memcg OOM kill. However, if swapping is enabled the
> > first page can be swapped before the second is allocated causing neither
> > limit to be exceeded, and no OOM kill to occur which results in a test
> > failure. Fix this by disabling swap in the test cgroup if it is enabled,
> > causing both pages to always be accounted under the same counter such
> > that memory.max (v2) / memory.limit_in_bytes (v1) causes an OOM kill.
>
> I see how this fixes the test for v2 but for v1 the write would fail
> with -EINVAL because memory.memsw.limit_in_bytes < memory.limit_in_bytes
> and swapout would still be possible (which it wasn't _on v1_ before this
> patch IIUC).
>
> IOW the testcase should not treat memory.swap.max (v2) and
> memory.memsw.limit_in_bytes (v1) as equivalent quantities.

Thanks Michal. I'm about to send a v2 where swap is disabled only in
memcg v2 but the memsw limit is still applied in memcg v1. Tested on
both versions of memcg this time.