Re: [PATCH v2 1/2] memcg: flush stats only if updated

[Shakeel Butt]

Hi Michal,

On Wed, Oct 13, 2021 at 11:01 AM Michal Koutný <mkoutny@xxxxxxxx> wrote:
>
> On Fri, Oct 01, 2021 at 12:00:39PM -0700, Shakeel Butt <shakeelb@xxxxxxxxxx> wrote:
> > In this patch we kept the stats update codepath very minimal and let the
> > stats reader side to flush the stats only when the updates are over a
> > specific threshold.  For now the threshold is (nr_cpus * CHARGE_BATCH).
>
> BTW, a noob question -- are the updates always single page sized?
>
> This is motivated by apples vs oranges comparison since the
>         nr_cpus * MEMCG_CHARGE_BATCH
> suggests what could the expected error be in pages (bytes). But it's mostly
> wrong since: a) uncertain single-page updates, b) various counter
> updates summed together. I wonder whether the formula can serve to
> provide at least some (upper) estimate.
>

Thanks for your review. This forces me to think more on this because each
update does not necessarily be a single page sized update e.g. adding a hugepage
to an LRU.

Though I think the error is time bounded by 2 seconds but in those 2 seconds
mathematically the error can be large. What do you think of the following
change? It will bound the error better within the 2 seconds window.