linux-kernel - Re: [RFC][PATCH v2 11/21] kvm: allocate page table pages from DRAM

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

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."