Re: Removing ->dirty_folio

[Matthew Wilcox <willy@infradead.org>]

On Tue, Aug 25, 2026 at 10:06:30PM +0200, Jann Horn wrote:
> On Tue, Aug 25, 2026 at 9:54 PM Matthew Wilcox <willy@infradead.org> wrote:
> > On Tue, Aug 25, 2026 at 09:35:57PM +0200, Jann Horn wrote:
> > > Could we strictly ban using get_user_pages*() for write access, and
> > > use the unpin_*() helpers to somehow enforce that folios are always
> > > dirtied on unpin? I guess the problem with that is that we have no
> > > state that tracks whether the pin was read-only, and finding free bits
> > > in struct page to keep track of this is hard?
> >
> > We'd need a count, not just a bit or two.  A pincount for all folios
> > is on its way (eventually) but I wans't planning on tracking writable vs
> > read-only pins.
> 
> My thinking was that once a folio has been pinned writably one time,
> it should be fine to mark it as dirty every time it is unpinned, even
> if some of those pins were read-only?

Ah, so the point of this proposal is to mark the folio dirty when it's
pinned.  Nobody clears the dirty flag at any point until it's written
back after being unpinned.