linux-kernel - Re: [PATCH v6 6/9] mm: multigenerational lru: aging

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Date:   Fri, 7 Jan 2022 14:11:29 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     Yu Zhao <yuzhao@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Hillf Danton <hdanton@...a.com>, Jens Axboe <axboe@...nel.dk>,
        Jesse Barnes <jsbarnes@...gle.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Jonathan Corbet <corbet@....net>,
        Matthew Wilcox <willy@...radead.org>,
        Mel Gorman <mgorman@...e.de>,
        Michael Larabel <Michael@...haellarabel.com>,
        Rik van Riel <riel@...riel.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Will Deacon <will@...nel.org>,
        Ying Huang <ying.huang@...el.com>,
        linux-arm-kernel@...ts.infradead.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        page-reclaim@...gle.com, x86@...nel.org,
        Konstantin Kharlamov <Hi-Angel@...dex.ru>
Subject: Re: [PATCH v6 6/9] mm: multigenerational lru: aging

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