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SubjectRe: [PATCH 06/18] mm, hugetlb: remove vma_need_reservation()
Hello, Naoya.

On Mon, Jul 29, 2013 at 01:52:52PM -0400, Naoya Horiguchi wrote:
> Hi,
>
> On Mon, Jul 29, 2013 at 02:31:57PM +0900, Joonsoo Kim wrote:
> > vma_need_reservation() can be substituted by vma_has_reserves()
> > with minor change. These function do almost same thing,
> > so unifying them is better to maintain.
>
> I think it could, but not with minor changes.
> vma_has_reserves is mostly the negation of the vma_needs_reservation,
> but not exactly (consider that vma(VM_NORESERVE) does not have nor
> need any reservation.)

Yes, currently not exactly same, but we can merge these functions.
I think that confusion comes from selection of base function. If I merge
vma_has_reserve() into vma_need_reservation(), it may be more trivial.

>
> > Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> >
> > diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> > index bf2ee11..ff46a2c 100644
> > --- a/mm/hugetlb.c
> > +++ b/mm/hugetlb.c
> > @@ -451,8 +451,18 @@ void reset_vma_resv_huge_pages(struct vm_area_struct *vma)
> > vma->vm_private_data = (void *)0;
> > }
> >
> > -/* Returns true if the VMA has associated reserve pages */
> > -static int vma_has_reserves(struct vm_area_struct *vma, long chg)
> > +/*
> > + * Determine if the huge page at addr within the vma has an associated
> > + * reservation. Where it does not we will need to logically increase
> > + * reservation and actually increase subpool usage before an allocation
> > + * can occur. Where any new reservation would be required the
> > + * reservation change is prepared, but not committed. Once the page
> > + * has been allocated from the subpool and instantiated the change should
> > + * be committed via vma_commit_reservation. No action is required on
> > + * failure.
> > + */
> > +static int vma_has_reserves(struct hstate *h,
> > + struct vm_area_struct *vma, unsigned long addr)
> > {
> > if (vma->vm_flags & VM_NORESERVE) {
> > /*
>
> Could you add more detailed comment on top of the function for better
> maintenability? What is the expected behavior, or what is the returned
> values for each case with what reasons?

Okay. I should do it.

> And this function is not a simple reserve checker any more, but it can
> change reservation maps, so it would be nice to give more suitable name,
> though I don't have any good suggestions.

Okay.

>
> > @@ -464,10 +474,22 @@ static int vma_has_reserves(struct vm_area_struct *vma, long chg)
> > * step. Currently, we don't have any other solution to deal
> > * with this situation properly, so add work-around here.
> > */
> > - if (vma->vm_flags & VM_MAYSHARE && chg == 0)
> > - return 1;
> > - else
> > - return 0;
> > + if (vma->vm_flags & VM_MAYSHARE) {
> > + struct address_space *mapping = vma->vm_file->f_mapping;
> > + struct inode *inode = mapping->host;
> > + pgoff_t idx = vma_hugecache_offset(h, vma, addr);
> > + struct resv_map *resv = inode->i_mapping->private_data;
>
> It would be nice if we can get resv_map from vma in a single function for
> VM_MAYSHARE, so can you add it on vma_resv_map?

Yes, that's good idea. I will consider it.

>
> > + long chg;
> > +
> > + chg = region_chg(resv, idx, idx + 1);
> > + if (chg < 0)
> > + return -ENOMEM;
> > +
> > + if (chg == 0)
> > + return 1;
> > + }
> > +
> > + return 0;
> > }
> >
> > /* Shared mappings always use reserves */
> > @@ -478,8 +500,16 @@ static int vma_has_reserves(struct vm_area_struct *vma, long chg)
> > * Only the process that called mmap() has reserves for
> > * private mappings.
> > */
> > - if (is_vma_resv_set(vma, HPAGE_RESV_OWNER))
> > + if (is_vma_resv_set(vma, HPAGE_RESV_OWNER)) {
> > + pgoff_t idx = vma_hugecache_offset(h, vma, addr);
> > + struct resv_map *resv = vma_resv_map(vma);
> > +
> > + /* Just for allocating region structure */
> > + if (region_chg(resv, idx, idx + 1) < 0)
> > + return -ENOMEM;
> > +
> > return 1;
> > + }
> >
> > return 0;
> > }
> > @@ -542,8 +572,7 @@ static struct page *dequeue_huge_page_node(struct hstate *h, int nid)
> >
> > static struct page *dequeue_huge_page_vma(struct hstate *h,
> > struct vm_area_struct *vma,
> > - unsigned long address, int avoid_reserve,
> > - long chg)
> > + unsigned long address, int avoid_reserve)
> > {
> > struct page *page = NULL;
> > struct mempolicy *mpol;
> > @@ -558,7 +587,7 @@ static struct page *dequeue_huge_page_vma(struct hstate *h,
> > * have no page reserves. This check ensures that reservations are
> > * not "stolen". The child may still get SIGKILLed
> > */
> > - if (!vma_has_reserves(vma, chg) &&
> > + if (!vma_has_reserves(h, vma, address) &&
> > h->free_huge_pages - h->resv_huge_pages == 0)
> > return NULL;
> >
> > @@ -578,7 +607,7 @@ retry_cpuset:
> > if (page) {
> > if (avoid_reserve)
> > break;
> > - if (!vma_has_reserves(vma, chg))
> > + if (!vma_has_reserves(h, vma, address))
> > break;
> >
> > h->resv_huge_pages--;
> > @@ -1077,42 +1106,6 @@ static void return_unused_surplus_pages(struct hstate *h,
> > }
> > }
> >
> > -/*
> > - * Determine if the huge page at addr within the vma has an associated
> > - * reservation. Where it does not we will need to logically increase
> > - * reservation and actually increase subpool usage before an allocation
> > - * can occur. Where any new reservation would be required the
> > - * reservation change is prepared, but not committed. Once the page
> > - * has been allocated from the subpool and instantiated the change should
> > - * be committed via vma_commit_reservation. No action is required on
> > - * failure.
> > - */
> > -static long vma_needs_reservation(struct hstate *h,
> > - struct vm_area_struct *vma, unsigned long addr)
> > -{
> > - struct address_space *mapping = vma->vm_file->f_mapping;
> > - struct inode *inode = mapping->host;
> > -
> > - if (vma->vm_flags & VM_MAYSHARE) {
> > - pgoff_t idx = vma_hugecache_offset(h, vma, addr);
> > - struct resv_map *resv = inode->i_mapping->private_data;
> > -
> > - return region_chg(resv, idx, idx + 1);
> > -
> > - } else if (!is_vma_resv_set(vma, HPAGE_RESV_OWNER)) {
> > - return 1;
> > -
> > - } else {
> > - long err;
> > - pgoff_t idx = vma_hugecache_offset(h, vma, addr);
> > - struct resv_map *resv = vma_resv_map(vma);
> > -
> > - err = region_chg(resv, idx, idx + 1);
> > - if (err < 0)
> > - return err;
> > - return 0;
> > - }
> > -}
> > static void vma_commit_reservation(struct hstate *h,
> > struct vm_area_struct *vma, unsigned long addr)
> > {
> > @@ -1140,8 +1133,7 @@ static struct page *alloc_huge_page(struct vm_area_struct *vma,
> > struct hugepage_subpool *spool = subpool_vma(vma);
> > struct hstate *h = hstate_vma(vma);
> > struct page *page;
> > - long chg;
> > - int ret, idx;
> > + int ret, idx, has_reserve;
> > struct hugetlb_cgroup *h_cg;
> >
> > idx = hstate_index(h);
> > @@ -1153,20 +1145,21 @@ 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)
> > + has_reserve = vma_has_reserves(h, vma, addr);
> > + if (has_reserve < 0)
> > return ERR_PTR(-ENOMEM);
> > - if (chg)
> > - if (hugepage_subpool_get_pages(spool, chg))
> > +
> > + if (!has_reserve && (hugepage_subpool_get_pages(spool, 1) < 0))
> > return ERR_PTR(-ENOSPC);
> > ret = hugetlb_cgroup_charge_cgroup(idx, pages_per_huge_page(h), &h_cg);
> > if (ret) {
> > - hugepage_subpool_put_pages(spool, chg);
> > + if (!has_reserve)
> > + hugepage_subpool_put_pages(spool, 1);
>
> It seems that this fixes the subpool accounting, so worth separating to
> another patch or writing on the description.

Okay!

Thanks.

>
> Thanks,
> Naoya Horiguchi
>
> > return ERR_PTR(-ENOSPC);
> > }
> > spin_lock(&hugetlb_lock);
> > - page = dequeue_huge_page_vma(h, vma, addr, avoid_reserve, chg);
> > + page = dequeue_huge_page_vma(h, vma, addr, avoid_reserve);
> > if (!page) {
> > spin_unlock(&hugetlb_lock);
> > page = alloc_buddy_huge_page(h, NUMA_NO_NODE);
> > @@ -1174,7 +1167,8 @@ static struct page *alloc_huge_page(struct vm_area_struct *vma,
> > hugetlb_cgroup_uncharge_cgroup(idx,
> > pages_per_huge_page(h),
> > h_cg);
> > - hugepage_subpool_put_pages(spool, chg);
> > + if (!has_reserve)
> > + hugepage_subpool_put_pages(spool, 1);
> > return ERR_PTR(-ENOSPC);
> > }
> > spin_lock(&hugetlb_lock);
> > @@ -2769,7 +2763,7 @@ retry:
> > * the spinlock.
> > */
> > if ((flags & FAULT_FLAG_WRITE) && !(vma->vm_flags & VM_SHARED))
> > - if (vma_needs_reservation(h, vma, address) < 0) {
> > + if (vma_has_reserves(h, vma, address) < 0) {
> > ret = VM_FAULT_OOM;
> > goto backout_unlocked;
> > }
> > @@ -2860,7 +2854,7 @@ int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
> > * consumed.
> > */
> > if ((flags & FAULT_FLAG_WRITE) && !huge_pte_write(entry)) {
> > - if (vma_needs_reservation(h, vma, address) < 0) {
> > + if (vma_has_reserves(h, vma, address) < 0) {
> > ret = VM_FAULT_OOM;
> > goto out_mutex;
> > }
> > --
> > 1.7.9.5
> >
>
> --
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