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

[Baolin Wang <baolin.wang@linux.alibaba.com>]

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@samsung.com/
> [2] https://gitlab.com/dkruces/linux-next/-/commits/next-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.

For anon shmem, we should ignore the length, which you always set it to 
PAGE_SIZE in patch [1].

[1] 
https://gitlab.com/dkruces/linux-next/-/commit/edf02311fd6d86b355d3aeb74e67c8da6de3c569

> @@ -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.