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

Thomas Hellström (VMware) thomas_os at
Wed Oct 2 09:21:01 UTC 2019

On 9/26/19 10:16 PM, Linus Torvalds wrote:
> On Thu, Sep 26, 2019 at 1:09 PM Thomas Hellström (VMware)
> <thomas_os at> 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:

(top three patched)

with users included here:

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.



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