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Date:   Fri, 22 Sep 2023 09:30:17 -0400
From:   Johannes Weiner <hannes@cmpxchg.org>
To:     Michal Hocko <mhocko@suse.com>
Cc:     Jeremi Piotrowski <jpiotrowski@linux.microsoft.com>,
        Shakeel Butt <shakeelb@google.com>,
        Roman Gushchin <roman.gushchin@linux.dev>,
        Muchun Song <muchun.song@linux.dev>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, patches@lists.linux.dev,
        Tejun Heo <tj@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel@vger.kernel.org, regressions@lists.linux.dev,
        mathieu.tortuyaux@gmail.com
Subject: Re: [REGRESSION] Re: [PATCH 6.1 033/219] memcg: drop
 kmem.limit_in_bytes
Message-ID: <20230922133017.GD124289@cmpxchg.org>
References: <4eb47d6a-b127-4aad-af30-896c3b9505b4@linux.microsoft.com>
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On Thu, Sep 21, 2023 at 01:21:54PM +0200, Michal Hocko wrote:
> @@ -3097,6 +3097,7 @@ static void obj_cgroup_uncharge_pages(struct obj_cgroup *objcg,
>  static int obj_cgroup_charge_pages(struct obj_cgroup *objcg, gfp_t gfp,
>  				   unsigned int nr_pages)
>  {
> +	struct page_counter *counter;
>  	struct mem_cgroup *memcg;
>  	int ret;
>  
> @@ -3107,6 +3108,10 @@ static int obj_cgroup_charge_pages(struct obj_cgroup *objcg, gfp_t gfp,
>  		goto out;
>  
>  	memcg_account_kmem(memcg, nr_pages);
> +
> +	/* There is no way to set up kmem hard limit so this operation cannot fail */
> +	if (!cgroup_subsys_on_dfl(memory_cgrp_subsys))
> +		WARN_ON(!page_counter_try_charge(&memcg->kmem, nr_pages, &counter));

This hunk doesn't look quite right.

static void memcg_account_kmem(struct mem_cgroup *memcg, int nr_pages)
{
	mod_memcg_state(memcg, MEMCG_KMEM, nr_pages);
	if (!cgroup_subsys_on_dfl(memory_cgrp_subsys)) {
		if (nr_pages > 0)
			page_counter_charge(&memcg->kmem, nr_pages);
		else
			page_counter_uncharge(&memcg->kmem, -nr_pages);
	}
}

Other than that, please add

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