Re: [PATCH v3] mm/mempolicy,hugetlb: Checking hstate for hugetlbfs page in vma_migratable

["Li Xinhai" <lixinhai.lxh@gmail.com>]

On 2020-01-16 at 08:09 Mike Kravetz wrote:
>On 1/15/20 5:39 AM, Li Xinhai wrote:
>> Checking hstate at early phase when isolating page, instead of during
>> unmap and move phase, to avoid useless isolation.
>>
>> Signed-off-by: Li Xinhai <lixinhai.lxh@gmail.com>
>> Cc: Michal Hocko <mhocko@suse.com>
>> Cc: Mike Kravetz <mike.kravetz@oracle.com>
>> ---
>>  include/linux/hugetlb_inline.h | 7 +++++++
>>  include/linux/mempolicy.h      | 5 ++---
>>  mm/hugetlb.c                   | 9 +++++++++
>>  3 files changed, 18 insertions(+), 3 deletions(-)
>>
>> diff --git a/include/linux/hugetlb_inline.h b/include/linux/hugetlb_inline.h
>> index 0660a03..fc07139 100644
>> --- a/include/linux/hugetlb_inline.h
>> +++ b/include/linux/hugetlb_inline.h
>> @@ -11,6 +11,8 @@ static inline bool is_vm_hugetlb_page(struct vm_area_struct *vma)
>>  return !!(vma->vm_flags & VM_HUGETLB);
>>  }
>> 
>> +extern bool vm_hugepage_migration_supported(struct vm_area_struct *vma);
>> +
>>  #else
>> 
>>  static inline bool is_vm_hugetlb_page(struct vm_area_struct *vma)
>> @@ -18,6 +20,11 @@ static inline bool is_vm_hugetlb_page(struct vm_area_struct *vma)
>>  return false;
>>  }
>> 
>> +static inline bool vm_hugepage_migration_supported(struct vm_area_struct *vma)
>> +{
>> +	return false;
>> +}
>> +
>>  #endif
>> 
>>  #endif
>> diff --git a/include/linux/mempolicy.h b/include/linux/mempolicy.h
>> index 5228c62..e9ed49e 100644
>> --- a/include/linux/mempolicy.h
>> +++ b/include/linux/mempolicy.h
>> @@ -185,10 +185,9 @@ static inline bool vma_migratable(struct vm_area_struct *vma)
>>  if (vma_is_dax(vma))
>>  return false;
>> 
>> -#ifndef CONFIG_ARCH_ENABLE_HUGEPAGE_MIGRATION
>> -	if (vma->vm_flags & VM_HUGETLB)
>> +	if (is_vm_hugetlb_page(vma) &&
>> +	!vm_hugepage_migration_supported(vma))
>>  return false;
>> -#endif
>> 
>>  /*
>>  * Migration allocates pages in the highest zone. If we cannot
>
>There are not many ways to work around the hugepage_migration_supported
>dependency issue.  I suppose you could have moved vma_migratable() into
>mm/mempolicy.c instead of being an inline in the header file.  However,
>it is probably best to do what you have done and hide the ugly stuff in
>the hugetlbfs files. 
Yes, that looks better, thanks. I will prepare new one.

>
>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
>> index dd8737a..8ce4a98 100644
>> --- a/mm/hugetlb.c
>> +++ b/mm/hugetlb.c
>> @@ -1316,6 +1316,15 @@ int PageHeadHuge(struct page *page_head)
>>  return get_compound_page_dtor(page_head) == free_huge_page;
>>  }
>> 
>> +bool vm_hugepage_migration_supported(struct vm_area_struct *vma)
>> +{
>> +	VM_BUG_ON_VMA(!is_vm_hugetlb_page(vma), vma);
>
>This VM_BUG_ON_VMA() seems unnecessary.  The only caller is the one
>added with this patch which is only called if is_vm_hugetlb_page(vma).
>Even though VM_BUG_ON() is only enabled if CONFIG_DEBUG_VM, many distros
>(including the one running my desktop) enable CONFIG_DEBUG_VM in their
>default kernel.
>
>--
>Mike Kravetz
>
>> +	if (hugepage_migration_supported(hstate_vma(vma)))
>> +	return true;
>> +
>> +	return false;
>> +}
>> +
>>  pgoff_t __basepage_index(struct page *page)
>>  {
>>  struct page *page_head = compound_head(page);
>>