Re: [PATCH v4] mm/mempolicy,hugetlb: Checking hstate for hugetlbfs page in vma_migratable

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

On 2020-01-16 at 17:56 Michal Hocko wrote:
>On Thu 16-01-20 04:11:25, Li Xinhai wrote:
>> Checking hstate at early phase when isolating page, instead of during
>> unmap and move phase, to avoid useless isolation.
>
>Could you be more specific what you mean by isolation and why does it
>matter? The patch description should really explain _why_ the change is
>needed or desirable. 

The changelog can be improved:

vma_migratable() is called to check if pages in vma can be migrated
before go ahead to isolate, unmap and move pages. For hugetlb pages,
hugepage_migration_supported(struct hstate *h) is one factor which
decide if migration is supported. In current code, this function is called
from unmap_and_move_huge_page(), after isolating page has
completed.
This patch checks hstate from vma_migratable() and avoids isolating pages
which are not supported.

>
>> 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.h   | 10 ++++++++++
>>  include/linux/mempolicy.h | 29 +----------------------------
>>  mm/mempolicy.c            | 28 ++++++++++++++++++++++++++++
>>  3 files changed, 39 insertions(+), 28 deletions(-)
>>
>> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
>> index 31d4920..c9d871d 100644
>> --- a/include/linux/hugetlb.h
>> +++ b/include/linux/hugetlb.h
>> @@ -598,6 +598,11 @@ static inline bool hugepage_migration_supported(struct hstate *h)
>>  return arch_hugetlb_migration_supported(h);
>>  }
>> 
>> +static inline bool vm_hugepage_migration_supported(struct vm_area_struct *vma)
>> +{
>> +	return hugepage_migration_supported(hstate_vma(vma));
>> +}
>> +
>>  /*
>>   * Movability check is different as compared to migration check.
>>   * It determines whether or not a huge page should be placed on
>> @@ -809,6 +814,11 @@ static inline bool hugepage_migration_supported(struct hstate *h)
>>  return false;
>>  }
>> 
>> +static inline bool vm_hugepage_migration_supported(struct vm_area_struct *vma)
>> +{
>> +	return false;
>> +}
>> +
>>  static inline bool hugepage_movable_supported(struct hstate *h)
>>  {
>>  return false;
>> diff --git a/include/linux/mempolicy.h b/include/linux/mempolicy.h
>> index 5228c62..8165278 100644
>> --- a/include/linux/mempolicy.h
>> +++ b/include/linux/mempolicy.h
>> @@ -173,34 +173,7 @@ int do_migrate_pages(struct mm_struct *mm, const nodemask_t *from,
>>  extern void mpol_to_str(char *buffer, int maxlen, struct mempolicy *pol);
>> 
>>  /* Check if a vma is migratable */
>> -static inline bool vma_migratable(struct vm_area_struct *vma)
>> -{
>> -	if (vma->vm_flags & (VM_IO | VM_PFNMAP))
>> -	return false;
>> -
>> -	/*
>> -	* DAX device mappings require predictable access latency, so avoid
>> -	* incurring periodic faults.
>> -	*/
>> -	if (vma_is_dax(vma))
>> -	return false;
>> -
>> -#ifndef CONFIG_ARCH_ENABLE_HUGEPAGE_MIGRATION
>> -	if (vma->vm_flags & VM_HUGETLB)
>> -	return false;
>> -#endif
>> -
>> -	/*
>> -	* Migration allocates pages in the highest zone. If we cannot
>> -	* do so then migration (at least from node to node) is not
>> -	* possible.
>> -	*/
>> -	if (vma->vm_file &&
>> -	gfp_zone(mapping_gfp_mask(vma->vm_file->f_mapping))
>> -	< policy_zone)
>> -	return false;
>> -	return true;
>> -}
>> +extern bool vma_migratable(struct vm_area_struct *vma);
>> 
>>  extern int mpol_misplaced(struct page *, struct vm_area_struct *, unsigned long);
>>  extern void mpol_put_task_policy(struct task_struct *);
>> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
>> index 067cf7d..8a01fb1 100644
>> --- a/mm/mempolicy.c
>> +++ b/mm/mempolicy.c
>> @@ -1714,6 +1714,34 @@ static int kernel_get_mempolicy(int __user *policy,
>> 
>>  #endif /* CONFIG_COMPAT */
>> 
>> +bool vma_migratable(struct vm_area_struct *vma)
>> +{
>> +	if (vma->vm_flags & (VM_IO | VM_PFNMAP))
>> +	return false;
>> +
>> +	/*
>> +	* DAX device mappings require predictable access latency, so avoid
>> +	* incurring periodic faults.
>> +	*/
>> +	if (vma_is_dax(vma))
>> +	return false;
>> +
>> +	if (is_vm_hugetlb_page(vma) &&
>> +	!vm_hugepage_migration_supported(vma))
>> +	return false;
>> +
>> +	/*
>> +	* Migration allocates pages in the highest zone. If we cannot
>> +	* do so then migration (at least from node to node) is not
>> +	* possible.
>> +	*/
>> +	if (vma->vm_file &&
>> +	gfp_zone(mapping_gfp_mask(vma->vm_file->f_mapping))
>> +	< policy_zone)
>> +	return false;
>> +	return true;
>> +}
>> +
>>  struct mempolicy *__get_vma_policy(struct vm_area_struct *vma,
>>  unsigned long addr)
>>  {
>> --
>> 1.8.3.1
>>
>
>--
>Michal Hocko
>SUSE Labs