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Date: Mon, 1 Jul 2024 19:12:32 +0800
From: Baolin Wang <baolin.wang@...ux.alibaba.com>
To: Bang Li <libang.li@...group.com>, Ryan Roberts <ryan.roberts@....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 17:43, Bang Li wrote:
> Hi, Baolin
>
> On 2024/7/1 16:33, 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.
>>
>> 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:
>>
>> 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)
>
> Thanks for the reference code. Currently, we only implement the mTHP of
> anonymous shmem, so we only need to handle anonymous shmem specially. As
> shown in the following code:
>
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -151,10 +151,14 @@ 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);
Nit: add a blank line after the declaration. Otherwise looks good to me.
> + if (!vma_is_anon_shmem(vma))
> + return global_huge? orders : 0;
> + return
> shmem_allowable_huge_orders(file_inode(vma->vm_file),
> + vma, vma->vm_pgoff,
> global_huge);
> + }
>
> if (!vma_is_anonymous(vma)) {
>
> Thanks,
> Bang
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