linux-kernel - Re: [PATCH v7 3/6] zswap: make shrinking memcg-aware

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Message-ID: <20231129151721.GC135852@cmpxchg.org>
Date:   Wed, 29 Nov 2023 10:17:21 -0500
From:   Johannes Weiner <hannes@...xchg.org>
To:     Nhat Pham <nphamcs@...il.com>
Cc:     akpm@...ux-foundation.org, cerasuolodomenico@...il.com,
        yosryahmed@...gle.com, sjenning@...hat.com, ddstreet@...e.org,
        vitaly.wool@...sulko.com, mhocko@...nel.org,
        roman.gushchin@...ux.dev, shakeelb@...gle.com,
        muchun.song@...ux.dev, chrisl@...nel.org, linux-mm@...ck.org,
        kernel-team@...a.com, linux-kernel@...r.kernel.org,
        cgroups@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kselftest@...r.kernel.org, shuah@...nel.org
Subject: Re: [PATCH v7 3/6] zswap: make shrinking memcg-aware

On Mon, Nov 27, 2023 at 03:45:57PM -0800, Nhat Pham wrote:
>  static void shrink_worker(struct work_struct *w)
>  {
>  	struct zswap_pool *pool = container_of(w, typeof(*pool),
>  						shrink_work);
> +	struct mem_cgroup *memcg;
>  	int ret, failures = 0;
>  
> +	/* global reclaim will select cgroup in a round-robin fashion. */
>  	do {
> -		ret = zswap_reclaim_entry(pool);
> -		if (ret) {
> -			zswap_reject_reclaim_fail++;
> -			if (ret != -EAGAIN)
> -				break;
> +		spin_lock(&zswap_pools_lock);
> +		memcg = pool->next_shrink =
> +			mem_cgroup_iter_online(NULL, pool->next_shrink, NULL, true);
> +
> +		/* full round trip */
> +		if (!memcg) {
> +			spin_unlock(&zswap_pools_lock);
>  			if (++failures == MAX_RECLAIM_RETRIES)
>  				break;
> +
> +			goto resched;
>  		}
> +
> +		/*
> +		 * Acquire an extra reference to the iterated memcg in case the
> +		 * original reference is dropped by the zswap offlining callback.
> +		 */
> +		css_get(&memcg->css);

struct mem_cgroup isn't defined when !CONFIG_MEMCG. This needs a
mem_cgroup_get() wrapper and a dummy function for no-memcg builds.

With that fixed, though, everything else looks good to me:

Acked-by: Johannes Weiner <hannes@...xchg.org>