Re: [PATCH RFC 2/6] mm: convert PG_balloon to PG_offline

[Matthew Wilcox]

On Wed, Nov 14, 2018 at 10:17:00PM +0100, David Hildenbrand wrote:
> Rename PG_balloon to PG_offline. This is an indicator that the page is
> logically offline, the content stale and that it should not be touched
> (e.g. a hypervisor would have to allocate backing storage in order for the
> guest to dump an unused page).  We can then e.g. exclude such pages from
> dumps.
> 
> In following patches, we will make use of this bit also in other balloon
> drivers.  While at it, document PGTABLE.

Thank you for documenting PGTABLE.  I didn't realise I also had this
document to update when I added PGTABLE.

> +++ b/Documentation/admin-guide/mm/pagemap.rst
> @@ -78,6 +78,8 @@ number of times a page is mapped.
>      23. BALLOON
>      24. ZERO_PAGE
>      25. IDLE
> +    26. PGTABLE
> +    27. OFFLINE

So the offline *user* bit is new ... even though the *kernel* bit
just renames the balloon bit.  I'm not sure how I feel about this.
I'm going to think about it some more.  Could you share your decision
process with us?

I have no objection to renaming the balloon bit inside the kernel; I
think that's a wise idea.  I'm just not sure whether we should rename
the user balloon bit rather than adding a new bit.