Re: [PATCH v7 2/8] iov_iter: Add a function to extract a page list from an iterator

[David Hildenbrand]

On 27.01.23 01:05, David Howells wrote:
> David Hildenbrand <david@xxxxxxxxxx> wrote:
>
> > As raised already somewhere in the whole discussion by me, the right way to
> > take such a long-term ping as vmsplice() does is to use
> > FOLL_PIN|FOLL_LONGTERM.
>
> So the pipe infrastructure would have to be able to pin pages instead of
> carrying refs on them?  What about pages just allocated and added to the pipe
> ring in normal pipe use?
Ordinary kernel allocations (alloc_page() ...) always have to be freed 
via put_page() and friends. Such allocations are unmovable as default 
and don't require any special care.

Pages mapped into user space are movable as default and might be placed 
on ZONE_MOVABLE/CMA memory (well, and might be swapped out). 
FOLL_LONGTERM makes sure to migrate these pages off of such problematic 
physical memory regions, such that we can safely pin them until eternity.

--
Thanks,

David / dhildenb