Re: [PATCH] mm/khugepaged: fix collapse_pte_mapped_thp() to allow anon_vma

[David Hildenbrand]

On 18.01.23 00:00, Zach O'Keefe wrote:
> On Mon, Jan 9, 2023 at 12:50 AM David Hildenbrand <david@xxxxxxxxxx> wrote:
> > > > > > > > Side note: set_huge_pmd() wins the award of "ugliest mm function of early
> > > > > > > > 2023". I was briefly concerned how do_set_pmd() decides whether the PMD can be
> > > > > > > > writable or not. Turns out it's communicated via vm_fault->flags. Just
> > > > > > > > horrible.
>
> Hey David,
>
> Sorry for the late response here.
>
> > > My first Linux award! :) At least it's not "worst mm security issue of
> > > early 2023". I'll take it!
> >
> > Good that you're not taking my words the wrong way.
> >
> > MADV_COLLAPSE is a very useful feature (especially also for THP tests
> > [1]). I wish I could have looked at some of the patches earlier. But we
> > cannot wait forever to get something merged, otherwise we'd never get
> > bigger changes upstream.
> >
> > ... so there is plenty of time left in 2023 to cleanup khugepaged.c :P
> >
> >
> > [1] https://lkml.kernel.org/r/20230104144905.460075-1-david@xxxxxxxxxx
>
> Yes, thank you for these tests. I have them open in another tab along
> with a mental TODO to take a closer look at them, and response
> half-written. In-place collapse of anonymous memory *is* something
> that I was interested in exploring later (I have a use-case for it;
> hugepage-aware malloc() implementations). I'm taking so long on it
> (sorry) b/c I need to review your point (2) (all PTE's mapping
> exclusively). Hopefully I can get to it shortly.

Cool, please let me know if you have any questions. Being able to 
in-place collapse a PTE-mapped anon THP again would be nice.

--
Thanks,

David / dhildenb