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

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Date: Mon, 1 Jul 2024 16:46:45 +0800
From: Baolin Wang <baolin.wang@...ux.alibaba.com>
To: Ryan Roberts <ryan.roberts@....com>, Bang Li <libang.li@...group.com>,
 hughd@...gle.com, akpm@...ux-foundation.org
Cc: david@...hat.com, 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 2024/7/1 16:40, 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.
> 
>>
>> IIUC, I agree with David's suggestion that the shmem_allowable_huge_orders()
>> helper function could be used in thp_vma_allowable_orders() to support shmem
>> mTHP. Something like:
> 
> I hadn't seen David's suggestion until after I sent my mail. But I think we are > both suggesting the same thing.

OK. Great :)