No, 3% was chosen in __vm_enough_memory() for LSMs as the comment in the
oom killer shows:
/*
* Root processes get 3% bonus, just like the __vm_enough_memory()
* implementation used by LSMs.
*/
and is described in Documentation/filesystems/proc.txt.
I think in cases of heuristics like this where we obviously want to give
some bonus to CAP_SYS_ADMIN that there is consistency with other bonuses
given elsewhere in the kernel.
The old heuristic divided the arbitrary badness score by 4 with
CAP_SYS_RESOURCE. The new heuristic doesn't consider it.
How is that more clean?
As a side-effect of being given more resources to allocate, those
applications are relatively unbounded in terms of memory consumption to
other tasks. Thus, it's possible that these applications are using a
massive amount of memory (say, 75%) and now with the proposed change a
task using 25% of memory would be killed instead. This increases the
liklihood that the CAP_SYS_RESOURCE thread will have to be killed
eventually, anyway, and the goal is to kill as few tasks as possible to
free sufficient amount of memory.
Since threads having CAP_SYS_RESOURCE have full control over their
oom_score_adj, they can take the additional precautions to protect
themselves if necessary. It doesn't need to be a part of the heuristic to
bias these tasks which will lead to the undesired result described above
by default rather than intentionally from userspace.
Then you would want to explicitly filter these tasks from oom kill just as
OOM_SCORE_ADJ_MIN works rather than giving them a memory quantity bonus.
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