linux-kernel - Re: [PATCH 3/3] mm: adjust vm_committed_as_batch according to vm overcommit policy

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Date:   Fri, 8 May 2020 04:24:48 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Feng Tang <feng.tang@...el.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Mel Gorman <mgorman@...e.de>,
        Kees Cook <keescook@...omium.org>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Iurii Zaikin <yzaikin@...gle.com>, andi.kleen@...el.com,
        tim.c.chen@...el.com, dave.hansen@...el.com, ying.huang@...el.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] mm: adjust vm_committed_as_batch according to vm
 overcommit policy

On Fri, May 08, 2020 at 03:25:17PM +0800, Feng Tang wrote:
> +void mm_compute_batch(void)
>  {
>  	u64 memsized_batch;
>  	s32 nr = num_present_cpus();
>  	s32 batch = max_t(s32, nr*2, 32);
> -
> -	/* batch size set to 0.4% of (total memory/#cpus), or max int32 */
> -	memsized_batch = min_t(u64, (totalram_pages()/nr)/256, 0x7fffffff);
> +	unsigned long ram_pages = totalram_pages();
> +
> +	/*
> +	 * For policy of OVERCOMMIT_NEVER, set batch size to 0.4%
> +	 * of (total memory/#cpus), and lift it to 6.25% for other
> +	 * policies to easy the possible lock contention for percpu_counter
> +	 * vm_committed_as, while the max limit is INT_MAX
> +	 */
> +	if (sysctl_overcommit_memory == OVERCOMMIT_NEVER)
> +		memsized_batch = min_t(u64, ram_pages/nr/256, INT_MAX);
> +	else
> +		memsized_batch = min_t(u64, ram_pages/nr/16, INT_MAX);
>  
>  	vm_committed_as_batch = max_t(s32, memsized_batch, batch);
> +	printk("vm_committed_as_batch = %d\n", vm_committed_as_batch);
>  }

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