Re: [PATCH] support "THPeligible" semantics for mTHP with anonymous shmem

[David Hildenbrand <david@redhat.com>]

On 01.07.24 10:50, Ryan Roberts wrote:
> On 01/07/2024 09:48, David Hildenbrand wrote:
>> On 01.07.24 10:40, Ryan Roberts wrote:
>>> On 01/07/2024 09:33, Baolin Wang wrote:
>>>>
>>>>
>>>> On 2024/7/1 15:55, Ryan Roberts wrote:
>>>>> On 28/06/2024 11:49, Bang Li wrote:
>>>>>> After the commit 7fb1b252afb5 ("mm: shmem: add mTHP support for
>>>>>> anonymous shmem"), we can configure different policies through
>>>>>> the multi-size THP sysfs interface for anonymous shmem. But
>>>>>> currently "THPeligible" indicates only whether the mapping is
>>>>>> eligible for allocating THP-pages as well as the THP is PMD
>>>>>> mappable or not for anonymous shmem, we need to support semantics
>>>>>> for mTHP with anonymous shmem similar to those for mTHP with
>>>>>> anonymous memory.
>>>>>>
>>>>>> Signed-off-by: Bang Li <libang.li@antgroup.com>
>>>>>> ---
>>>>>>     fs/proc/task_mmu.c      | 10 +++++++---
>>>>>>     include/linux/huge_mm.h | 11 +++++++++++
>>>>>>     mm/shmem.c              |  9 +--------
>>>>>>     3 files changed, 19 insertions(+), 11 deletions(-)
>>>>>>
>>>>>> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
>>>>>> index 93fb2c61b154..09b5db356886 100644
>>>>>> --- a/fs/proc/task_mmu.c
>>>>>> +++ b/fs/proc/task_mmu.c
>>>>>> @@ -870,6 +870,7 @@ static int show_smap(struct seq_file *m, void *v)
>>>>>>     {
>>>>>>         struct vm_area_struct *vma = v;
>>>>>>         struct mem_size_stats mss = {};
>>>>>> +    bool thp_eligible;
>>>>>>           smap_gather_stats(vma, &mss, 0);
>>>>>>     @@ -882,9 +883,12 @@ static int show_smap(struct seq_file *m, void *v)
>>>>>>           __show_smap(m, &mss, false);
>>>>>>     -    seq_printf(m, "THPeligible:    %8u\n",
>>>>>> -           !!thp_vma_allowable_orders(vma, vma->vm_flags,
>>>>>> -               TVA_SMAPS | TVA_ENFORCE_SYSFS, THP_ORDERS_ALL));
>>>>>> +    thp_eligible = !!thp_vma_allowable_orders(vma, vma->vm_flags,
>>>>>> +                        TVA_SMAPS | TVA_ENFORCE_SYSFS, THP_ORDERS_ALL);
>>>>>> +    if (vma_is_anon_shmem(vma))
>>>>>> +        thp_eligible =
>>>>>> !!shmem_allowable_huge_orders(file_inode(vma->vm_file),
>>>>>> +                            vma, vma->vm_pgoff, thp_eligible);
>>>>>
>>>>> Afraid I haven't been following the shmem mTHP support work as much as I would
>>>>> have liked, but is there a reason why we need a separate function for shmem?
>>>>
>>>> Since shmem_allowable_huge_orders() only uses shmem specific logic to determine
>>>> if huge orders are allowable, there is no need to complicate the
>>>> thp_vma_allowable_orders() function by adding more shmem related logic, making
>>>> it more bloated. In my view, providing a dedicated helper
>>>> shmem_allowable_huge_orders(), specifically for shmem, simplifies the logic.
>>>
>>> My point was really that a single interface (thp_vma_allowable_orders) should be
>>> used to get this information. I have no strong opinon on how the implementation
>>> of that interface looks. What you suggest below seems perfectly reasonable to me.
>>
>> Right. thp_vma_allowable_orders() might require some care as discussed in other
>> context (cleanly separate dax and shmem handling/orders). But that would be
>> follow-up cleanups.
> 
> Are you planning to do that, or do you want me to send a patch?

I'm planning on looking into some details, especially the interaction 
with large folios in the pagecache. I'll let you know once I have a 
better idea what actually should be done :)

-- 
Cheers,

David / dhildenb