Re: [PATCH 1/2] mm: Allow architectures to request 'old' entries when prefaulting

[Kirill A. Shutemov]

On Sun, Dec 27, 2020 at 11:38:22AM -0800, Linus Torvalds wrote:
> On Sat, Dec 26, 2020 at 6:38 PM Hugh Dickins <hughd@xxxxxxxxxx> wrote:
> >
> > This patch (like its antecedents) moves the pte_unmap_unlock() from
> > after do_fault_around()'s "check if the page fault is solved" into
> > filemap_map_pages() itself (which apparently does not NULLify vmf->pte
> > after unmapping it, which is poor, but good for revealing this issue).
> > That looks cleaner, but of course there was a very good reason for its
> > original positioning.
> 
> Good catch.
> 
> > Maybe you want to change the ->map_pages prototype, to pass down the
> > requested address too, so that it can report whether the requested
> > address was resolved or not.  Or it could be left to __do_fault(),
> > or even to a repeated fault; but those would be less efficient.
> 
> Let's keep the old really odd "let's unlock in the caller" for now,
> and minimize the changes.

I did what Hugh proposed and it got clear to my eyes. It gets somewhat
large, but take a look.

The patch below incorporates all fixups from the thread.