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    SubjectRe: [PATCH 06/18] mm, hugetlb: remove vma_need_reservation()
    On Tue, Jul 30, 2013 at 11:19:58PM +0530, Aneesh Kumar K.V wrote:
    > Joonsoo Kim <iamjoonsoo.kim@lge.com> writes:
    >
    > > 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 found the resulting code confusing and complex. I am sure there is
    > more that what is explained in the commit message. If you are just doing
    > this for cleanup, may be we should avoid doing this ?

    I may need this cleanup, because I want to decide whether this page comes
    from reserved page pool or not, more clearly. Without this, this decision
    can be harder.
    Anyway, I should describe the purpose of this patch in detail.

    Thanks.

    >
    >
    > >
    > > 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) {
    > > /*
    > > @@ -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;
    > > + 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);
    > > 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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    > see: http://www.linux-mm.org/ .
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