Re: [PATCH resend] memcg: introduce per-memcg reclaim interface

Andrew Morton
2022-04-01T00:33:56Z

On Thu, 31 Mar 2022 08:41:51 +0000 Yosry Ahmed <yosryahmed@google.com> wrote:

> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -6355,6 +6355,38 @@ static ssize_t memory_oom_group_write(struct kernfs_open_file *of,
> return nbytes;
> }
>
> +static ssize_t memory_reclaim(struct kernfs_open_file *of, char *buf,
> + size_t nbytes, loff_t off)
> +{
> + struct mem_cgroup *memcg = mem_cgroup_from_css(of_css(of));
> + unsigned int nr_retries = MAX_RECLAIM_RETRIES;
> + unsigned long nr_to_reclaim, nr_reclaimed = 0;
> + int err;
> +
> + buf = strstrip(buf);
> + err = page_counter_memparse(buf, "", &nr_to_reclaim);
> + if (err)
> + return err;
> +
> + while (nr_reclaimed < nr_to_reclaim) {
> + unsigned long reclaimed;
> +
> + if (signal_pending(current))
> + break;
> +
> + reclaimed = try_to_free_mem_cgroup_pages(memcg,
> + nr_to_reclaim - nr_reclaimed,
> + GFP_KERNEL, true);
> +
> + if (!reclaimed && !nr_retries--)
> + break;
> +
> + nr_reclaimed += reclaimed;
> + }

Is there any way in which this can be provoked into triggering the
softlockup detector?

Is it optimal to do the MAX_RECLAIM_RETRIES loop in the kernel?
Would additional flexibility be gained by letting userspace handle
retrying?