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Message-ID: <516aa6b3-617c-4642-b12b-0c5f5b33d1c9@arm.com>
Date: Mon, 1 Jul 2024 09:40:34 +0100
From: Ryan Roberts <ryan.roberts@....com>
To: Baolin Wang <baolin.wang@...ux.alibaba.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 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.
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index c7ce28f6b7f3..9677fe6cf478 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -151,10 +151,13 @@ unsigned long __thp_vma_allowable_orders(struct
> vm_area_struct *vma,
> * Must be done before hugepage flags check since shmem has its
> * own flags.
> */
> - if (!in_pf && shmem_file(vma->vm_file))
> - return shmem_is_huge(file_inode(vma->vm_file), vma->vm_pgoff,
> - !enforce_sysfs, vma->vm_mm, vm_flags)
> - ? orders : 0;
> + if (!in_pf && shmem_file(vma->vm_file)) {
> + bool global_huge = shmem_is_huge(file_inode(vma->vm_file),
> vma->vm_pgoff,
> + !enforce_sysfs, vma->vm_mm, vm_flags);
> +
> + return shmem_allowable_huge_orders(file_inode(vma->vm_file),
> + vma, vma->vm_pgoff, global_huge);
> + }
>
> if (!vma_is_anonymous(vma)) {
> /*
>
>> Couldn't (shouldn't) thp_vma_allowable_orders() be taught to handle shmem too?
>>
>>> + seq_printf(m, "THPeligible: %8u\n", thp_eligible);
>>> if (arch_pkeys_enabled())
>>> seq_printf(m, "ProtectionKey: %8u\n", vma_pkey(vma));
>>> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
>>> index 212cca384d7e..f87136f38aa1 100644
>>> --- a/include/linux/huge_mm.h
>>> +++ b/include/linux/huge_mm.h
>>> @@ -267,6 +267,10 @@ unsigned long thp_vma_allowable_orders(struct
>>> vm_area_struct *vma,
>>> return __thp_vma_allowable_orders(vma, vm_flags, tva_flags, orders);
>>> }
>>> +unsigned long shmem_allowable_huge_orders(struct inode *inode,
>>> + struct vm_area_struct *vma, pgoff_t index,
>>> + bool global_huge);
>>> +
>>> struct thpsize {
>>> struct kobject kobj;
>>> struct list_head node;
>>> @@ -460,6 +464,13 @@ static inline unsigned long
>>> thp_vma_allowable_orders(struct vm_area_struct *vma,
>>> return 0;
>>> }
>>> +static inline unsigned long shmem_allowable_huge_orders(struct inode *inode,
>>> + struct vm_area_struct *vma, pgoff_t index,
>>> + bool global_huge)
>>> +{
>>> + return 0;
>>> +}
>>> +
>>> #define transparent_hugepage_flags 0UL
>>> #define thp_get_unmapped_area NULL
>>> diff --git a/mm/shmem.c b/mm/shmem.c
>>> index d495c0701a83..aa85df9c662a 100644
>>> --- a/mm/shmem.c
>>> +++ b/mm/shmem.c
>>> @@ -1622,7 +1622,7 @@ static gfp_t limit_gfp_mask(gfp_t huge_gfp, gfp_t
>>> limit_gfp)
>>> }
>>> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
>>> -static unsigned long shmem_allowable_huge_orders(struct inode *inode,
>>> +unsigned long shmem_allowable_huge_orders(struct inode *inode,
>>> struct vm_area_struct *vma, pgoff_t index,
>>> bool global_huge)
>>> {
>>> @@ -1707,13 +1707,6 @@ static unsigned long shmem_suitable_orders(struct
>>> inode *inode, struct vm_fault
>>> return orders;
>>> }
>>> #else
>>> -static unsigned long shmem_allowable_huge_orders(struct inode *inode,
>>> - struct vm_area_struct *vma, pgoff_t index,
>>> - bool global_huge)
>>> -{
>>> - return 0;
>>> -}
>>> -
>>> static unsigned long shmem_suitable_orders(struct inode *inode, struct
>>> vm_fault *vmf,
>>> struct address_space *mapping, pgoff_t index,
>>> unsigned long orders)
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