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

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Message-ID: <20170109165712.GA3058@redhat.com>
Date:   Mon, 9 Jan 2017 11:57:12 -0500
From:   Jerome Glisse <jglisse@...hat.com>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Balbir Singh <bsingharora@...il.com>, 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 Mon, Jan 09, 2017 at 08:21:25AM -0800, Dave Hansen wrote:
> 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?

VM_BUG_ON_PAGE ok with you ? It is just a safety net, i can simply drop that
patch if people have too much feeling about it.

Cheers,
Jérôme