Re: [PATCH v5 2/8] mm: factor zone-device page init helpers out of __init_zone_device_page

[Li Zhe]

On Mon, 6 Jul 2026 15:47:43 +0200, david@xxxxxxxxxx wrote:

> On 7/6/26 13:50, Li Zhe wrote:
> > On Mon, Jul 6, 2026 at 11:13:45AM +0200, david@xxxxxxxxxx wrote:
> >
> >>> +static inline bool pagemap_resets_refcount(const struct dev_pagemap *pgmap)
> >>> +{
> >>> +	/*
> >>> +	 * MEMORY_DEVICE_GENERIC pages regain a refcount of 1 in the free
> >>> +	 * path. The remaining ZONE_DEVICE types start from 0 here and raise
> >>> +	 * the count again when the allocator or driver hands the page out.
> >>> +	 */
> >>> +	switch (pgmap->type) {
> >>> +	case MEMORY_DEVICE_FS_DAX:
> >>> +	case MEMORY_DEVICE_PRIVATE:
> >>> +	case MEMORY_DEVICE_COHERENT:
> >>> +	case MEMORY_DEVICE_PCI_P2PDMA:
> >>> +		return false;
> >>> +	case MEMORY_DEVICE_GENERIC:
> >>> +		return true;
> >>> +	default:
> >>> +		WARN_ONCE(1, "Unknown memory type!");
> >>> +		return true;
> >>
> >> Wouldn't the compiler warn if we would define a new type but forgot to update it
> >> here? We're using an enum, and I thought the compiler would bail out in that case.
> >>
> >> Or are we scared of some other garbage ending up in there?
> >>
> >> Apart from that LGTM.
> >
> > Thanks.
> >
> > I will drop the default case in v6 so a newly added enum memory_type
> > value is easier to catch during build review.
> >
> > I will move the WARN_ONCE() after the switch so we still keep a
> > runtime guard in case some invalid value ever shows up there.
> 
> If the compiler complains, we won't need the WARN_ONCE().

Thanks. I will drop the WARN_ONCE() as well in v6.

Thanks,
Zhe