linux-kernel - Re: [HMM v15 01/16] mm/free_hot_cold_page: catch ZONE

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Message-ID: <591ef5e3-54a9-da61-bca6-f30641bebe88@intel.com>
Date:   Mon, 9 Jan 2017 08:21:25 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Balbir Singh <bsingharora@...il.com>,
        Jérôme Glisse <jglisse@...hat.com>
Cc:     akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, John Hubbard <jhubbard@...dia.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Ross Zwisler <ross.zwisler@...ux.intel.com>
Subject: Re: [HMM v15 01/16] mm/free_hot_cold_page: catch ZONE_DEVICE pages

On 01/09/2017 01:19 AM, Balbir Singh wrote:
>> +	/*
>> +	 * This should never happen ! Page from ZONE_DEVICE always must have an
>> +	 * active refcount. Complain about it and try to restore the refcount.
>> +	 */
>> +	if (is_zone_device_page(page)) {
>> +		VM_BUG_ON_PAGE(is_zone_device_page(page), page);
> This can be VM_BUG_ON_PAGE(1, page), hopefully the compiler does the right thing
> here. I suspect this should be a BUG_ON, independent of CONFIG_DEBUG_VM

BUG_ON() means "kill the machine dead".  Do we really want a guaranteed
dead machine if someone screws up their refcounting?