On 21.05.2021 17:07, Benjamin Berg wrote:
> On Fri, 2021-05-21 at 15:25 +0300, Andrei Borzenkov wrote:
>> systemd offers MemoryLow for an individual units. It actually sets
>> memory.low cgroup attribute, so this is OK. The problem is according to
>> kernel dcouemtation, memory.low is limited by value set in parent
>> cgroup and all parent cgroups have memory.low=0:
>> which implies setting on lead cgroup has no effect.
>> Is it necessary to explicitly set it on every ancestor? There is no
>> clarification in systemd documentation and value is applied without any
> Yes, you need to set it on all ancestors, and the documentation
> mentions this:
> For a protection to be effective, it is generally required to
> set a corresponding allocation on all ancestors, which is
> then distributed between children (with the exception of the
> root slice). Any MemoryMin= or MemoryLow= allocation that is
> not explicitly distributed to specific children is used to
> create a shared protection for all children. As this is a
> shared protection, the children will freely compete for the
OK, it is in upstream now, was not in my version and I did not pay
attention to web page. Sorry.
I guess I expected systemd to somehow handle it, given that it knows all
the settings, knows exact hierarchy and is the sole master of cgroup tree.
> Depending on the kernel versions there may be some other caveats:
> Units may have their children use a default "memory.min" or
> "memory.low" value by specifying DefaultMemoryMin= or
> DefaultMemoryLow=, which has the same semantics as MemoryMin=
> and MemoryLow=. This setting does not affect "memory.min" or
> "memory.low" in the unit itself. Using it to set a default
> child allocation is only useful on kernels older than 5.7,
> which do not support the "memory_recursiveprot" cgroup2 mount
> You need to configure it correctly in various locations. Personally, I
> would suggest taking a look at uresourced. It will correctly set a
> configurable memory protection, enables some other cgroup features and
> tracks the currently active user. Fedora is shipping it by default and
> it appears to work well there.
That's overkill for my purposes. This is single user system and all I am
trying to do is to prevent swapping out Wayland composer to avoid
waiting several minutes to unblank screen. I am fine with setting values
Thanks for the pointers.
>  https://gitlab.freedesktop.org/benzea/uresourced and