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Message-ID: <9b511ad9-0ba1-e896-4eb5-0e91ca4b97ab@huawei.com>
Date: Fri, 30 Apr 2021 09:57:16 +0800
From: Miaohe Lin <linmiaohe@...wei.com>
To: David Hildenbrand <david@...hat.com>, <akpm@...ux-foundation.org>
CC: <ziy@...dia.com>, <william.kucharski@...cle.com>,
<willy@...radead.org>, <yang.shi@...ux.alibaba.com>,
<aneesh.kumar@...ux.ibm.com>, <rcampbell@...dia.com>,
<songliubraving@...com>, <kirill.shutemov@...ux.intel.com>,
<riel@...riel.com>, <hannes@...xchg.org>, <minchan@...nel.org>,
<linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>
Subject: Re: [PATCH v2 3/5] mm/huge_memory.c: add missing read-only THP
checking in transparent_hugepage_enabled()
On 2021/4/29 22:57, David Hildenbrand wrote:
> On 29.04.21 15:26, Miaohe Lin wrote:
>> Since commit 99cb0dbd47a1 ("mm,thp: add read-only THP support for
>> (non-shmem) FS"), read-only THP file mapping is supported. But it
>> forgot to add checking for it in transparent_hugepage_enabled().
>> To fix it, we add checking for read-only THP file mapping and also
>> introduce helper transhuge_vma_enabled() to check whether thp is
>> enabled for specified vma to reduce duplicated code.
>>
>> Fixes: 99cb0dbd47a1 ("mm,thp: add read-only THP support for (non-shmem) FS")
>> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
>> ---
>> include/linux/huge_mm.h | 21 +++++++++++++++++----
>> mm/huge_memory.c | 6 ++++++
>> mm/khugepaged.c | 4 +---
>> mm/shmem.c | 3 +--
>> 4 files changed, 25 insertions(+), 9 deletions(-)
>>
>> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
>> index 0a526f211fec..f460b74619fc 100644
>> --- a/include/linux/huge_mm.h
>> +++ b/include/linux/huge_mm.h
>> @@ -115,6 +115,16 @@ extern struct kobj_attribute shmem_enabled_attr;
>> extern unsigned long transparent_hugepage_flags;
>> +static inline bool transhuge_vma_enabled(struct vm_area_struct *vma,
>> + unsigned long vm_flags)
>
> You're passing the vma already, why do you pass vma->vm_flags separately? It's sufficient to pass in the vma only.
>
Many thanks for comment! IMO, vm_flags may not always equal to vma->vm_flags. When hugepage_vma_check()
is called from collapse_pte_mapped_thp, vma_flags = vma->vm_flags | VM_HUGEPAGE. So I think we should
pass vm_flags here.
>> +{
>> + /* Explicitly disabled through madvise. */
>> + if ((vm_flags & VM_NOHUGEPAGE) ||
>> + test_bit(MMF_DISABLE_THP, &vma->vm_mm->flags))
>> + return false;
>> + return true;
>> +}
>> +
>> /*
>> * to be used on vmas which are known to support THP.
>> * Use transparent_hugepage_enabled otherwise
>> @@ -128,15 +138,12 @@ static inline bool __transparent_hugepage_enabled(struct vm_area_struct *vma)
>> if (transparent_hugepage_flags & (1 << TRANSPARENT_HUGEPAGE_NEVER_DAX))
>> return false;
>> - if (vma->vm_flags & VM_NOHUGEPAGE)
>> + if (!transhuge_vma_enabled(vma, vma->vm_flags))
>> return false;
>> if (vma_is_temporary_stack(vma))
>> return false;
>> - if (test_bit(MMF_DISABLE_THP, &vma->vm_mm->flags))
>> - return false;
>> -
>> if (transparent_hugepage_flags & (1 << TRANSPARENT_HUGEPAGE_FLAG))
>> return true;
>> @@ -362,6 +369,12 @@ static inline bool transhuge_vma_suitable(struct vm_area_struct *vma,
>> return false;
>> }
>> +static inline bool transhuge_vma_enabled(struct vm_area_struct *vma,
>> + unsigned long vm_flags)
>> +{
>> + return false;
>> +}
>> +
>> static inline void prep_transhuge_page(struct page *page) {}
>> static inline bool is_transparent_hugepage(struct page *page)
>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>> index 76ca1eb2a223..e24a96de2e37 100644
>> --- a/mm/huge_memory.c
>> +++ b/mm/huge_memory.c
>> @@ -68,12 +68,18 @@ bool transparent_hugepage_enabled(struct vm_area_struct *vma)
>> /* The addr is used to check if the vma size fits */
>> unsigned long addr = (vma->vm_end & HPAGE_PMD_MASK) - HPAGE_PMD_SIZE;
>> + if (!transhuge_vma_enabled(vma, vma->vm_flags))
>> + return false;
>> if (!transhuge_vma_suitable(vma, addr))
>> return false;
>> if (vma_is_anonymous(vma))
>> return __transparent_hugepage_enabled(vma);
>> if (vma_is_shmem(vma))
>> return shmem_huge_enabled(vma);
>> + if (IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && vma->vm_file &&
>> + !inode_is_open_for_write(vma->vm_file->f_inode) &&
>> + (vma->vm_flags & VM_EXEC))
>> + return true;
>
> Nit: I'm really wondering why we have 3 different functions that sound like they are doing the same thing
>
> transparent_hugepage_enabled(vma)
> transhuge_vma_enabled()
> transhuge_vma_suitable()
>
> Which check belongs where? Does it really have to be that complicated?
>
IMO, transhuge_vma_suitable() checks whether pgoff , vm_start and vm_end is possible for thp.
transhuge_vma_enabled() checks whether thp is explicitly disabled through madvise.
And transparent_hugepage_enabled() use these helpers to get the conclusion whether thp is
enabled for specified vma.
Any suggestions?
Thanks again!
>> return false;
>> }
>> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
>> index 6c0185fdd815..d97b20fad6e8 100644
>> --- a/mm/khugepaged.c
>> +++ b/mm/khugepaged.c
>> @@ -442,9 +442,7 @@ static inline int khugepaged_test_exit(struct mm_struct *mm)
>> static bool hugepage_vma_check(struct vm_area_struct *vma,
>> unsigned long vm_flags)
>> {
>> - /* Explicitly disabled through madvise. */
>> - if ((vm_flags & VM_NOHUGEPAGE) ||
>> - test_bit(MMF_DISABLE_THP, &vma->vm_mm->flags))
>> + if (!transhuge_vma_enabled(vma, vm_flags))
>> return false;
>> /* Enabled via shmem mount options or sysfs settings. */
>> diff --git a/mm/shmem.c b/mm/shmem.c
>> index a08cedefbfaa..1dcbec313c70 100644
>> --- a/mm/shmem.c
>> +++ b/mm/shmem.c
>> @@ -4032,8 +4032,7 @@ bool shmem_huge_enabled(struct vm_area_struct *vma)
>> loff_t i_size;
>> pgoff_t off;
>> - if ((vma->vm_flags & VM_NOHUGEPAGE) ||
>> - test_bit(MMF_DISABLE_THP, &vma->vm_mm->flags))
>> + if (!transhuge_vma_enabled(vma, vma->vm_flags))
>> return false;
>> if (shmem_huge == SHMEM_HUGE_FORCE)
>> return true;
>>
>
>
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