Re: [PATCH] sched/numa: Fix NULL pointer access to mm_struct durng task swap

[Libo Chen]

On 7/3/25 05:36, Peter Zijlstra wrote:
> On Thu, Jul 03, 2025 at 05:20:47AM -0700, Libo Chen wrote:
> 
>> I agree. The other parts, schedstat and vmstat, are still quite helpful.
>> Also tracepoints are more expensive than counters once enabled, I think
>> that's too much for just counting numbers.
> 
> I'm not generally a fan of eBPF, but supposedly it is really good for
> stuff like this. 
> 

Yeah but not nearly as good as, for example, __schedstat_inc(var) which
probably only takes a few CPU cycles if var is in the right place. eBPF
is gonna take a whole bunch of sequences to even get to updating an eBPF
map which itself is much more expensive than __schedstat_inc(var).

For one, __migrate_swap_task() happens when dst node is fully busy (most
likely src node is full as well), so the overhead of ebpf could be quite
noticeable.


Libo
> Attaching to a tracepoint and distributing into cgroup buckets seems
> like it should be a trivial script.