Re: [PATCH] mm/memcontrol.c: drains percpu charge caches in memory.reclaim

[Michal Koutný]

On Thu, Nov 10, 2022 at 11:35:34AM -0800, Yosry Ahmed <yosryahmed@xxxxxxxxxx> wrote:
> OTOH, it will reduce the page counters, so if userspace is relying on
> memory.current to gauge how much reclaim they want to do, it will make
> it "appear" like the usage dropped.

Assuming memory.current is used to drive the proactive reclaim, then
this patch makes some sense (and is slightly better than draining upon
every memory.current read(2)).

I just think the commit message should explain the real mechanics of
this.

> The difference in perceived usage coming from draining the stock IIUC
> has an upper bound of 63 * PAGE_SIZE (< 256 KB with 4KB pages), I
> wonder if this is really significant anyway.

times nr_cpus (if memcg had stocks all over the place).

Michal

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