linux-kernel - Re: [RFC] high preempt off latency in vfree path

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Message-ID: <20160323024402.GA27856@tassilo.jf.intel.com>
Date:	Tue, 22 Mar 2016 19:44:02 -0700
From:	Andi Kleen <ak@...ux.intel.com>
To:	Joel Fernandes <joelaf@...126.com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org, tj@...nel.org,
	linux-rt-users@...r.kernel.org, Nick Piggin <npiggin@...e.de>
Subject: Re: [RFC] high preempt off latency in vfree path

> (1)
> One is we reduce the number of lazy_max_pages (right now its around 32MB per core worth of pages).
> 
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index aa3891e..2720f4f 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -564,7 +564,7 @@ static unsigned long lazy_max_pages(void)
> 
>         log = fls(num_online_cpus());
> 
> -       return log * (32UL * 1024 * 1024 / PAGE_SIZE);
> +       return log * (8UL * 1024 * 1024 / PAGE_SIZE);
>  }

This seems like the right fix to me.  Perhaps even make it somewhat smaller.

Even on larger systems it's probably fine because they have a lot more
cores/threads these days, so it will be still sufficiently large.

-Andi