Re: [RFC PATCH] mm: memcontrol: don't account swap failures not due to cgroup limits

[Michal Koutný]

On Thu, Feb 02, 2023 at 10:30:40AM -0800, Yosry Ahmed <yosryahmed@xxxxxxxxxx> wrote:
> > b) Only count cgroup swap events when they are actually due to a
> >    cgroup's own limit. Exclude failures that are due to physical swap
> >    shortage or other system-level conditions (like !THP_SWAP). Also
> >    count them at the level where the limit is configured, which may be
> >    above the local cgroup that holds the page-to-be-swapped.
> >
> >    This is in line with how memory.swap.high, memory.high and
> >    memory.max events are counted.
> >
> >    However, it's a change in documented behavior.
> 
> This option makes sense to me, but I can't speak to the change of
> documented behavior. However, looking at the code, it seems like if we do this
> the "max" & "fail" counters become effectively the same. "fail" would
> not provide much value then.
> 
> I wonder if it makes sense to have both, and clarify that "fail" -
> "max" would be non-limit based failures (e.g. ran out of swap space),
> or would this cause confusion as to whether those non-limit failures
> were transient (THP fallback) or eventual?

I somewhat second this.

Perhaps, could the patch (and arguments) be split in two:
1) count .max events on respective limit's level (other limits consistency),
2) redefine (remove?) memory.swap.fail events?

Michal

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