Re: [PATCH v2 1/2] mm: memcg: refactor page state unit helpers

[Michal Koutný]

On Thu, Oct 05, 2023 at 02:31:03AM -0700, Yosry Ahmed <yosryahmed@xxxxxxxxxx> wrote:
> I am not really sure what you mean here.

My "vision" is to treat WORKINGSET_ entries as events.
That would mean implementing per-node tracking for vm_event_item
(costlier?).
That would mean node_stat_item and vm_event_item being effectively
equal, so they could be merged in one.
That would be situation to come up with new classification based on use
cases (e.g. precision/timeliness requirements, state vs change
semantics).

(Do not take this as blocker of the patch 1/2, I rather used the
opportunity to discuss a greater possible cleanup.)

> We don't track things like OOM_KILL and DROP_PAGECACHE per memcg as
> far as I can tell.

Ah, good. (I forgot only subset of entries is relevant for memcgs.)

> This will mean that WORKINGSET_* state will become more stale. We will
> need 4096 as many updates as today to get a flush. These are used by
> internal flushers (reclaim), and are exposed to userspace. I am not
> sure we want to do that.

snapshot_refaults() doesn't seem to follow after flush
and
workigset_refault()'s flush doesn't seem to preceed readers

Is the flush misplaced or have I overlooked something?
(If the former, it seems to work good enough even with the current
flushing heuristics :-))


Michal

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