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Subject: Re: [RFC][PATCH v2 11/21] kvm: allocate page table pages from DRAM
References: <20181226131446.330864849@intel.com>
 <20181226133351.703380444@intel.com>
From: Dave Hansen <dave.hansen@intel.com>
Message-ID: <b99ef113-a9c1-f580-0fee-9f258b861391@intel.com>
Date: Wed, 2 Jan 2019 08:47:25 -0800
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Sender: owner-linux-mm@kvack.org
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To: Fengguang Wu <fengguang.wu@intel.com>, Andrew Morton <akpm@linux-foundation.org>
Cc: Linux Memory Management List <linux-mm@kvack.org>, Yao Yuan <yuan.yao@intel.com>, kvm@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>, Fan Du <fan.du@intel.com>, Peng Dong <dongx.peng@intel.com>, Huang Ying <ying.huang@intel.com>, Liu Jingqi <jingqi.liu@intel.com>, Dong Eddie <eddie.dong@intel.com>, Zhang Yi <yi.z.zhang@linux.intel.com>, Dan Williams <dan.j.williams@intel.com>

On 12/26/18 5:14 AM, Fengguang Wu wrote:
> +static unsigned long __get_dram_free_pages(gfp_t gfp_mask)
> +{
> +       struct page *page;
> +
> +       page = __alloc_pages(GFP_KERNEL_ACCOUNT, 0, numa_node_id());
> +       if (!page)
> +	       return 0;
> +       return (unsigned long) page_address(page);
> +}

There seems to be a ton of *policy* baked into these patches.  For
instance: thou shalt not allocate page tables pages from PMEM.  That's
surely not a policy we want to inflict on every Linux user until the end
of time.

I think the more important question is how we can have the specific
policy that this patch implements, but also leave open room for other
policies, such as: "I don't care how slow this VM runs, minimize the
amount of fast memory it eats."