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

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Date: Mon, 1 Jul 2024 09:50:59 +0100
From: Ryan Roberts <ryan.roberts@....com>
To: David Hildenbrand <david@...hat.com>,
 Baolin Wang <baolin.wang@...ux.alibaba.com>, Bang Li
 <libang.li@...group.com>, hughd@...gle.com, akpm@...ux-foundation.org
Cc: wangkefeng.wang@...wei.com, ziy@...dia.com, linux-kernel@...r.kernel.org,
 linux-mm@...ck.org
Subject: Re: [PATCH] support "THPeligible" semantics for mTHP with anonymous
 shmem

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@...group.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?