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Message-ID: <8d9e501a-0645-4b78-809a-7c9f49f2106d@arm.com>
Date: Wed, 3 Jul 2024 11:25:27 +0100
From: Ryan Roberts <ryan.roberts@....com>
To: Bang Li <libang.li@...group.com>, ughd@...gle.com,
akpm@...ux-foundation.org
Cc: david@...hat.com, wangkefeng.wang@...wei.com,
baolin.wang@...ux.alibaba.com, ioworker0@...il.com, ziy@...dia.com,
linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v2] mm: thp: support "THPeligible" semantics for mTHP with
anonymous shmem
On 03/07/2024 08:33, Bang Li wrote:
> Hi Ryan,
>
> Thanks for the review!
>
> On 2024/7/2 16:18, Ryan Roberts wrote:
>> On 02/07/2024 03:34, 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>
>>> ---
>>> Changes since v1 [1]:
>>> - Put anonymous shmem mthp related logic into
>>> thp_vma_allowable_orders() (per David)
>>>
>>> [1]
>>> https://lore.kernel.org/linux-mm/20240628104926.34209-1-libang.li@antgroup.com/
>>> ---
>>> include/linux/huge_mm.h | 11 +++++++++++
>>> mm/huge_memory.c | 13 +++++++++----
>>> mm/shmem.c | 9 +--------
>>> 3 files changed, 21 insertions(+), 12 deletions(-)
>>>
>>> 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/huge_memory.c b/mm/huge_memory.c
>>> index c7ce28f6b7f3..ea377bb4af91 100644
>>> --- a/mm/huge_memory.c
>>> +++ b/mm/huge_memory.c
>>> @@ -151,10 +151,15 @@ 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);
>>> +
>>> + if (!vma_is_anon_shmem(vma))
>>> + return global_huge? orders : 0;
>>
>> nit: missing space before '?'
>
> Yes, thanks.
>
>>
>>> + return shmem_allowable_huge_orders(file_inode(vma->vm_file),
>>> + vma, vma->vm_pgoff, global_huge);
>>
>> What's the rationale for splitting these functions into shmem_is_huge() and
>> shmem_allowable_huge_orders()? Why not just have a single
>> shmem_allowable_huge_orders() that tells you the answer?
>>
>
> Currently, shmem_is_huge() is used for all shmem implementations to determine
> whether the conditions for using THP are met. And shmem_allowable_huge_orders()
> is currently mainly used for anonymous shmem's mTHP to obtain all orders that
> meet the conditions. In my opinion, there is no problem in separating these two
> functions. In the future, when mTHP of other shmem types is also implemented,
> will shmem_is_huge() be unnecessary?
Personally, I consider shmem_is_huge() to be superfluous; If you have one
function, shmem_allowable_huge_orders(), that gives you all the information you
need. If the inode only allows PMD-size, then only return that bit in the field.
IMHO removing shmem_is_huge() would make things more readable.
Thanks,
Ryan
>
> Thanks,
> Bang
>
>>> + }
>>> if (!vma_is_anonymous(vma)) {
>>> /*
>>> 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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