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

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Message-ID: <YlA754XNFAmWQcm6@dschatzberg-fedora-PC0Y6AEN.dhcp.thefacebook.com>
Date:   Fri, 8 Apr 2022 09:43:03 -0400
From:   Dan Schatzberg <schatzberg.dan@...il.com>
To:     Yosry Ahmed <yosryahmed@...gle.com>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        David Rientjes <rientjes@...gle.com>,
        Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>,
        Jonathan Corbet <corbet@....net>,
        Shuah Khan <shuah@...nel.org>, Yu Zhao <yuzhao@...gle.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Wei Xu <weixugc@...gle.com>, Greg Thelen <gthelen@...gle.com>,
        Chen Wandun <chenwandun@...wei.com>,
        Vaibhav Jain <vaibhav@...ux.ibm.com>,
        Michal Koutný <mkoutny@...e.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>, cgroups@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-kselftest@...r.kernel.org,
        Michal Hocko <mhocko@...e.com>
Subject: Re: [PATCH v3 1/4] memcg: introduce per-memcg reclaim interface

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!