Re: [PATCH v2 14/20] mm, hugetlb: call vma_needs_reservation before entering alloc_huge_page()

[Aneesh Kumar K.V]

"Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx> writes:

> Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> writes:
>
>> In order to validate that this failure is reasonable, we need to know
>> whether allocation request is for reserved or not on caller function.
>> So moving vma_needs_reservation() up to the caller of alloc_huge_page().
>> There is no functional change in this patch and following patch use
>> this information.
>>
>> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
>>
>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
>> index 8dff972..bc666cf 100644
>> --- a/mm/hugetlb.c
>> +++ b/mm/hugetlb.c
>> @@ -1110,13 +1110,11 @@ static void vma_commit_reservation(struct hstate *h,
>>  }
>>
>>  static struct page *alloc_huge_page(struct vm_area_struct *vma,
>> -				    unsigned long addr, int avoid_reserve)
>> +				    unsigned long addr, int use_reserve)
>>  {
>>  	struct hugepage_subpool *spool = subpool_vma(vma);
>>  	struct hstate *h = hstate_vma(vma);
>>  	struct page *page;
>> -	long chg;
>> -	bool use_reserve;
>>  	int ret, idx;
>>  	struct hugetlb_cgroup *h_cg;
>>
>> @@ -1129,10 +1127,6 @@ static struct page *alloc_huge_page(struct vm_area_struct *vma,
>>  	 * need pages and subpool limit allocated allocated if no reserve
>>  	 * mapping overlaps.
>>  	 */
>> -	chg = vma_needs_reservation(h, vma, addr);
>> -	if (chg < 0)
>> -		return ERR_PTR(-ENOMEM);
>> -	use_reserve = (!chg && !avoid_reserve);
>>  	if (!use_reserve)
>>  		if (hugepage_subpool_get_pages(spool, 1))
>>  			return ERR_PTR(-ENOSPC);
>> @@ -2504,6 +2498,8 @@ static int hugetlb_cow(struct mm_struct *mm, struct vm_area_struct *vma,
>>  	struct hstate *h = hstate_vma(vma);
>>  	struct page *old_page, *new_page;
>>  	int outside_reserve = 0;
>> +	long chg;
>> +	bool use_reserve;
>>  	unsigned long mmun_start;	/* For mmu_notifiers */
>>  	unsigned long mmun_end;		/* For mmu_notifiers */
>>
>> @@ -2535,7 +2531,17 @@ retry_avoidcopy:
>>
>>  	/* Drop page_table_lock as buddy allocator may be called */
>>  	spin_unlock(&mm->page_table_lock);
>> -	new_page = alloc_huge_page(vma, address, outside_reserve);
>> +	chg = vma_needs_reservation(h, vma, address);
>> +	if (chg == -ENOMEM) {
>
> why not 
>
>     if (chg < 0) ?
>
> Should we try to unmap the page from child and avoid cow here ?. May be
> with outside_reserve = 1 we will never have vma_needs_reservation fail.
> Any how it would be nice to document why this error case is different
> from alloc_huge_page error case.
>

I guess patch  16 address this . So if we do if (chg < 0) we are good
here.

Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxxxxxxx>

-aneesh

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