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

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Message-ID: <597ac51e-3f27-4606-8647-395bb4e60df4@redhat.com>
Date: Mon, 1 Jul 2024 10:48:21 +0200
From: David Hildenbrand <david@...hat.com>
To: Ryan Roberts <ryan.roberts@....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 01.07.24 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.

-- 
Cheers,

David / dhildenb