On 09.12.24 18:36, Claudio Imbrenda wrote:
On Wed, 4 Dec 2024 16:58:52 +0100
David Hildenbrand <david@xxxxxxxxxx> wrote:
On 03.12.24 20:51, Matthew Wilcox wrote:
I've pushed out a new tree to
git://git.infradead.org/users/willy/pagecache.git shrunk-page
aka
http://git.infradead.org/?p=users/willy/pagecache.git;a=shortlog;h=refs/heads/shrunk-page
The observant will notice that it doesn't actually shrink struct page
yet. However, we're getting close. What it does do is rename
page->index to page->__folio_index to prevent new users of page->index
from showing up.
BTW, I was wondering how often we convert a page to a folio to then
access folio->index / folio->mapping and not actually having a folio (in
the future).
I suspect this will need quite some changes to get it right, and I would
count that as "less obvious".
Calling PageAnon() on anything mapped into user space page tables might
be one such case, for example.
There are (I believe) three build failures in that tree:
- fb_defio
- fbtft
- s390's gmap (and vsie? is that the same thing?)
Not completely (vsie (nested VMs) uses shadow gmap, ordinary VMs use
ordinary gmap) , but they are very related (-> KVM implementation on s390x).
I know that Claudio is working on some changes, but not sure how that
would affect gmap's usage of page->index.
After I'm done, we won't use page->index anymore.
The changes I'm working on are massive, it's very impractical to push
everything at once, so I'm refactoring and splitting smaller and more
manageable (and reviewable) series.
This means that it will take some time before I'm done (I'm *hoping*
to be done for 6.15)
Thanks for the information. So for the time being, we could likely
switch to page->private.
One question may be whether these (not-user-space) page tables should at
some point deserve a dedicated memdesc. But likely the question is what
it will all look like after your rework.
--
Cheers,
David / dhildenb
