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SubjectRe: [PATCH v2 14/20] mm, hugetlb: call vma_needs_reservation before entering alloc_huge_page()
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"Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com> writes:

> Joonsoo Kim <iamjoonsoo.kim@lge.com> 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@lge.com>
>>
>> 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@linux.vnet.ibm.com>

-aneesh



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