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From:   "Huang, Ying" <ying.huang@intel.com>
To:     Yu Zhao <yuzhao@google.com>
Cc:     Xing Zhengjun <zhengjun.xing@linux.intel.com>,
        akpm@linux-foundation.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, tim.c.chen@linux.intel.com,
        Shakeel Butt <shakeelb@google.com>,
        Michal Hocko <mhocko@suse.com>, wfg@mail.ustc.edu.cn
Subject: Re: [RFC] mm/vmscan.c: avoid possible long latency caused by
 too_many_isolated()
References: <20210416023536.168632-1-zhengjun.xing@linux.intel.com>
        <7b7a1c09-3d16-e199-15d2-ccea906d4a66@linux.intel.com>
        <YIGuvh70JbE1Cx4U@google.com>
        <7a0fecab-f9e1-ad39-d55e-01e574a35484@linux.intel.com>
        <YIMsykToLKUVMWbZ@google.com>
Date:   Sun, 25 Apr 2021 08:48:22 +0800
In-Reply-To: <YIMsykToLKUVMWbZ@google.com> (Yu Zhao's message of "Fri, 23 Apr
        2021 14:23:38 -0600")
Message-ID: <87fszfxk89.fsf@yhuang6-desk1.ccr.corp.intel.com>
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Yu Zhao <yuzhao@google.com> writes:
[snip]

> @@ -2966,13 +2938,20 @@ static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
>  			/* need some check for avoid more shrink_zone() */
>  		}
>  
> -		/* See comment about same check for global reclaim above */
> -		if (zone->zone_pgdat == last_pgdat)
> -			continue;
> -		last_pgdat = zone->zone_pgdat;
>  		shrink_node(zone->zone_pgdat, sc);
>  	}
>  
> +	if (last_pgdat)
> +		atomic_dec(&last_pgdat->nr_reclaimers);
> +	else if (should_retry) {
> +		/* wait a bit for the reclaimer. */
> +		if (!schedule_timeout_killable(HZ / 10))

Once we reached here, even accidentally, the caller needs to sleep at
least 100ms.  How about use a semaphore for pgdat->nr_reclaimers?  Then
the sleeper can be waken up when the resource is considered enough.

Best Regards,
Huang, Ying

> +			goto retry;
> +
> +		/* We are about to die and free our memory. Return now. */
> +		sc->nr_reclaimed += SWAP_CLUSTER_MAX;
> +	}
> +
>  	/*
>  	 * Restore to original mask to avoid the impact on the caller if we
>  	 * promoted it to __GFP_HIGHMEM.

[snip]