Re: [PATCH 0/2] s390: Remove uses of page->index

[David Hildenbrand <david@redhat.com>]

On 19.12.24 17:52, Matthew Wilcox wrote:
> On Thu, Dec 19, 2024 at 05:33:32PM +0100, David Hildenbrand wrote:
>> On 19.12.24 17:22, Matthew Wilcox (Oracle) wrote:
>>> These two patches compile ... I can promise nothing more than that.
>>>
>>> David suggested to me that the gmap code really should be using ptdesc,
>>> and I think I agree with him.  The vsie code looks quite different
>>> and probably shouldn't be using a ptdesc, but we can use page->private
>>> instead of page->index.  It's not yet clear to me if we'll ever manage
>>> to get rid of page->private.
>>
>> Just curious, does that mean that memdesc would always contain these
>> additional 8 bytes?
> 
> Eventually we'll have a choice to make.
> 
> 1. Shrink struct page to 8 bytes, but we'll need to allocate a 32 byte
>     memdesc for all the current users of page->private
> 2. Shrink struct page to 16 bytes
> 
> I genuinely don't know which will be better for the whole system.
> 
> If you're asking because we can defer some of the mapcount
> work by using the 8 bytes of page->private to store mapcount, then
> yes, let's do that.

Yeah, it could give us a bit more time, until we know that we can just 
get rid of it in all kernel configs. But let's see if that is still a 
problem when we're getting closer to removing them.

-- 
Cheers,

David / dhildenb