Re: Ack to merge through DRM? WAS Re: [PATCH v2 1/5] mm: Add write-protect and clean utilities for address space ranges

[Thomas HellstrÃm (VMware)]

On 10/2/19 3:18 PM, Kirill A. Shutemov wrote:
> On Wed, Oct 02, 2019 at 11:21:01AM +0200, Thomas HellstrÃm (VMware) wrote:
> > On 9/26/19 10:16 PM, Linus Torvalds wrote:
> > > On Thu, Sep 26, 2019 at 1:09 PM Thomas HellstrÃm (VMware)
> > > <thomas_os@xxxxxxxxxxxx> wrote:
> > > > That said, if people are OK with me modifying the assert in
> > > > pud_trans_huge_lock() and make __walk_page_range non-static, it should
> > > > probably be possible to make it work, yes.
> > > I don't think you need to modify that assert at all.
> > >
> > > That thing only exists when there's a "pud_entry" op in the walker,
> > > and then you absolutely need to have that mmap_lock.
> > >
> > > As far as I can tell, you fundamentally only ever work on a pte level
> > > in your address space walker already and actually have a WARN_ON() on
> > > the pud_huge thing, so no pud entry can possibly apply.
> > >
> > > So no, the assert in pud_trans_huge_lock() does not seem to be a
> > > reason not to just use the existing page table walkers.
> > >
> > > And once you get rid of the walking, what is left? Just the "iterate
> > > over the inode mappings" part. Which could just be done in
> > > mm/pagewalk.c, and then you don't even need to remove the static.
> > >
> > > So making it be just another walking in pagewalk.c would seem to be
> > > the simplest model.
> > >
> > > Call it "walk_page_mapping()". And talk extensively about how the
> > > locking differs a lot from the usual "walk_page_vma()" things.
> > >
> > > The then actual "apply" functions (what a horrid name) could be in the
> > > users. They shouldn't be mixed in with the walking functions anyway.
> > > They are callbacks, not walkers.
> > >
> > >                Linus
> > Linus, Kirill
> >
> > I've pushed a reworked version based on the pagewalk code here:
> >
> > https://cgit.freedesktop.org/~thomash/linux/log/?h=pagewalk
> >
> > (top three patched)
> >
> > with users included here:
> >
> > https://cgit.freedesktop.org/~thomash/linux/log/?h=coherent-rebased
> >
> > Do you think this could work? The reason that the "mm: Add write-protect and
> > clean.." code is still in mm as a set of helpers, is of course that much of
> > the needed functionality is not exported, presumably since we want to keep
> > page table manipulation in mm.
> Could you post it to the mailing list? It's easier to review this way.
Sure.

/Thomas