Date:   Fri, 7 Jan 2022 14:11:29 +0100
From:   Michal Hocko <mhocko@suse.com>
To:     Yu Zhao <yuzhao@google.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andi Kleen <ak@linux.intel.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Hillf Danton <hdanton@sina.com>, Jens Axboe <axboe@kernel.dk>,
        Jesse Barnes <jsbarnes@google.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Jonathan Corbet <corbet@lwn.net>,
        Matthew Wilcox <willy@infradead.org>,
        Mel Gorman <mgorman@suse.de>,
        Michael Larabel <Michael@michaellarabel.com>,
        Rik van Riel <riel@surriel.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Will Deacon <will@kernel.org>,
        Ying Huang <ying.huang@intel.com>,
        linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        page-reclaim@google.com, x86@kernel.org,
        Konstantin Kharlamov <Hi-Angel@yandex.ru>
Subject: Re: [PATCH v6 6/9] mm: multigenerational lru: aging
Message-ID: <Ydg8AeE6JIUnC+ps@dhcp22.suse.cz>
References: <20220104202227.2903605-1-yuzhao@google.com>
 <20220104202227.2903605-7-yuzhao@google.com>
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On Tue 04-01-22 13:22:25, Yu Zhao wrote:
[...]
> +static void lru_gen_age_node(struct pglist_data *pgdat, struct scan_control *sc)
> +{
> +	struct mem_cgroup *memcg;
> +	bool success = false;
> +	unsigned long min_ttl = READ_ONCE(lru_gen_min_ttl);
> +
> +	VM_BUG_ON(!current_is_kswapd());
> +
> +	current->reclaim_state->mm_walk = &pgdat->mm_walk;
> +
> +	memcg = mem_cgroup_iter(NULL, NULL, NULL);
> +	do {
> +		struct lruvec *lruvec = mem_cgroup_lruvec(memcg, pgdat);
> +
> +		if (age_lruvec(lruvec, sc, min_ttl))
> +			success = true;
> +
> +		cond_resched();
> +	} while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)));
> +
> +	if (!success && mutex_trylock(&oom_lock)) {
> +		struct oom_control oc = {
> +			.gfp_mask = sc->gfp_mask,
> +			.order = sc->order,
> +		};
> +
> +		if (!oom_reaping_in_progress())
> +			out_of_memory(&oc);
> +
> +		mutex_unlock(&oom_lock);
> +	}

Why do you need to trigger oom killer from this path? Why cannot you
rely on the page allocator to do that like we do now?
-- 
Michal Hocko
SUSE Labs