Re: [PATCH v3 1/4] memcg: introduce per-memcg reclaim interface

[Dan Schatzberg]

On Fri, Apr 08, 2022 at 04:57:40AM +0000, Yosry Ahmed wrote:
> +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);

Is there a reason not to support "max"? Empty string seems odd to me
here.

> +	if (err)
> +		return err;
> +
> +	while (nr_reclaimed < nr_to_reclaim) {
> +		unsigned long reclaimed;
> +
> +		if (signal_pending(current))
> +			break;

I think this should be `return -EINTR;`

> +
> +		reclaimed = try_to_free_mem_cgroup_pages(memcg,
> +						nr_to_reclaim - nr_reclaimed,
> +						GFP_KERNEL, true);
> +
> +		if (!reclaimed && !nr_retries--)
> +			break;

Here you can just `return -EAGAIN;`

> +
> +		nr_reclaimed += reclaimed;
> +	}
> +
> +	return nr_reclaimed < nr_to_reclaim ? -EAGAIN : nbytes;

Then this can just be `return nbytes;`

I'm very much in favor of this new interface. Thanks for working on
it!