Re: [PATCH v3 0/6] add mTHP support for anonymous shmem

[Baolin Wang]

On 2024/6/4 20:05, Daniel Gomez wrote:
> On Tue, Jun 04, 2024 at 05:45:20PM +0800, Baolin Wang wrote:
> > On 2024/6/4 16:18, Daniel Gomez wrote:
> > > On Fri, May 31, 2024 at 01:13:48PM +0200, David Hildenbrand wrote:
> > > > > > As a default, we should not be using large folios / mTHP for any shmem,
> > > > > > just like we did with THP via shmem_enabled. This is what this series
> > > > > > currently does, and is aprt of the whole mTHP user-space interface design.
> > > > > >
> > > > > > Further, the mTHP controls should control all of shmem, not only
> > > > > > "anonymous shmem".
> > > > >
> > > > > Yes, that's what I thought and in my TODO list.
> > > >
> > > > Good, it would be helpful to coordinate with Daniel and Pankaj.
> > >
> > > I've integrated patches 11 and 12 from the lsf RFC thread [1] on top of Baolin's
> > > v3 patches. You may find a version in my integration branch here [2]. I can
> > > attach them here if it's preferred.
> > >
> > > [1] https://lore.kernel.org/all/20240515055719.32577-1-da.gomez@xxxxxxxxxxx/
> > > [2] https://protect2.fireeye.com/v1/url?k=a23e7c06-c3b56926-a23ff749-74fe485fb347-371ca2bfd5d9869f&q=1&e=6974304e-a786-4255-93a7-57498540241c&u=https%3A%2F%2Fgitlab.com%2Fdkruces%2Flinux-next%2F-%2Fcommits%2Fnext-20240604-shmem-mthp
> > >
> > > The point here is to combine the large folios strategy I proposed with mTHP
> > > user controls. Would it make sense to limit the orders to the mapping order
> > > calculated based on the size and index?
> >
> > IMO, for !anon shmem, this change makes sense to me. We should respect the
> > size and mTHP should act as a order filter.
>
> What about respecing the size when within_size flag is enabled? Then, 'always'
> would allocate mTHP enabled folios, regardless of the size. And 'never'
> would ignore mTHP and size. So, 'never' can be used for this 'safe' boot case
> mentioned in the discussion.

Looks reasonable to me. What do you think, David?

And what about 'advise' option? Silimar to 'within_size'?

> > For anon shmem, we should ignore the length, which you always set it to
> > PAGE_SIZE in patch [1].
> >
> > [1] https://protect2.fireeye.com/v1/url?k=0d75a0c6-6cfeb5e6-0d742b89-74fe485fb347-904fa75c8efebdc2&q=1&e=6974304e-a786-4255-93a7-57498540241c&u=https%3A%2F%2Fgitlab.com%2Fdkruces%2Flinux-next%2F-%2Fcommit%2Fedf02311fd6d86b355d3aeb74e67c8da6de3c569
>
> Since we are ignoring the length, we should ignore any value being passed.
>
> > > @@ -1765,6 +1798,10 @@ static struct folio *shmem_alloc_and_add_folio(struct vm_fault *vmf,
> > >
> > >                   order = highest_order(suitable_orders);
> > >                   while (suitable_orders) {
> > > +                       if (order > mapping_order) {
> > > +                               order = next_order(&suitable_orders, order);
> > > +                               continue;
> > > +                       }
> > >                           pages = 1UL << order;
> > >                           index = round_down(index, pages);
> > >                           folio = shmem_alloc_folio(gfp, order, info, index);
> > >
> > > Note: The branch still need to be adapted to include !anon mm.