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


> + page_cache_release(old_page);
> +
> + /* Caller expects lock to be held */
> + spin_lock(&mm->page_table_lock);
> + return VM_FAULT_OOM;
> + }
> + use_reserve = !chg && !outside_reserve;
> +
> + new_page = alloc_huge_page(vma, address, use_reserve);
>
> if (IS_ERR(new_page)) {
> long err = PTR_ERR(new_page);
> @@ -2664,6 +2670,8 @@ static int hugetlb_no_page(struct mm_struct *mm, struct vm_area_struct *vma,
> struct page *page;
> struct address_space *mapping;
> pte_t new_pte;
> + long chg;
> + bool use_reserve;
>
> /*
> * Currently, we are forced to kill the process in the event the
> @@ -2689,7 +2697,15 @@ retry:
> size = i_size_read(mapping->host) >> huge_page_shift(h);
> if (idx >= size)
> goto out;
> - page = alloc_huge_page(vma, address, 0);
> +
> + chg = vma_needs_reservation(h, vma, address);
> + if (chg == -ENOMEM) {

if (chg < 0)

> + ret = VM_FAULT_OOM;
> + goto out;
> + }
> + use_reserve = !chg;
> +
> + page = alloc_huge_page(vma, address, use_reserve);
> if (IS_ERR(page)) {
> ret = PTR_ERR(page);
> if (ret == -ENOMEM)
> --
> 1.7.9.5



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