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SubjectRe: [PATCH 02/10] hugetlb: add allocate function for hugepage migration
On Wed, Sep 08, 2010 at 10:19:33AM +0900, Naoya Horiguchi wrote:
> We can't use existing hugepage allocation functions to allocate hugepage
> for page migration, because page migration can happen asynchronously with
> the running processes and page migration users should call the allocation
> function with physical addresses (not virtual addresses) as arguments.
>
> ChangeLog since v3:
> - unify alloc_buddy_huge_page() and alloc_buddy_huge_page_node()
>
> ChangeLog since v2:
> - remove unnecessary get/put_mems_allowed() (thanks to David Rientjes)
>
> ChangeLog since v1:
> - add comment on top of alloc_huge_page_no_vma()
>
> Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
> Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
> ---
> include/linux/hugetlb.h | 3 ++
> mm/hugetlb.c | 79 ++++++++++++++++++++++++++++++++---------------
> 2 files changed, 57 insertions(+), 25 deletions(-)
>
> diff --git v2.6.36-rc2/include/linux/hugetlb.h v2.6.36-rc2/include/linux/hugetlb.h
> index f479700..0b73c53 100644
> --- v2.6.36-rc2/include/linux/hugetlb.h
> +++ v2.6.36-rc2/include/linux/hugetlb.h
> @@ -228,6 +228,8 @@ struct huge_bootmem_page {
> struct hstate *hstate;
> };
>
> +struct page *alloc_huge_page_node(struct hstate *h, int nid);
> +
> /* arch callback */
> int __init alloc_bootmem_huge_page(struct hstate *h);
>
> @@ -303,6 +305,7 @@ static inline struct hstate *page_hstate(struct page *page)
>
> #else
> struct hstate {};
> +#define alloc_huge_page_node(h, nid) NULL
> #define alloc_bootmem_huge_page(h) NULL
> #define hstate_file(f) NULL
> #define hstate_vma(v) NULL
> diff --git v2.6.36-rc2/mm/hugetlb.c v2.6.36-rc2/mm/hugetlb.c
> index 6871b41..f526228 100644
> --- v2.6.36-rc2/mm/hugetlb.c
> +++ v2.6.36-rc2/mm/hugetlb.c
> @@ -466,11 +466,23 @@ static void enqueue_huge_page(struct hstate *h, struct page *page)
> h->free_huge_pages_node[nid]++;
> }
>
> +static struct page *dequeue_huge_page_node(struct hstate *h, int nid)
> +{
> + struct page *page;
> +
> + if (list_empty(&h->hugepage_freelists[nid]))
> + return NULL;
> + page = list_entry(h->hugepage_freelists[nid].next, struct page, lru);
> + list_del(&page->lru);
> + h->free_huge_pages--;
> + h->free_huge_pages_node[nid]--;
> + return page;
> +}
> +

Ok, this is fine because all you are doing is splitting
dequeue_huge_page_vma()

> static struct page *dequeue_huge_page_vma(struct hstate *h,
> struct vm_area_struct *vma,
> unsigned long address, int avoid_reserve)
> {
> - int nid;
> struct page *page = NULL;
> struct mempolicy *mpol;
> nodemask_t *nodemask;
> @@ -496,19 +508,13 @@ static struct page *dequeue_huge_page_vma(struct hstate *h,
>
> for_each_zone_zonelist_nodemask(zone, z, zonelist,
> MAX_NR_ZONES - 1, nodemask) {
> - nid = zone_to_nid(zone);
> - if (cpuset_zone_allowed_softwall(zone, htlb_alloc_mask) &&
> - !list_empty(&h->hugepage_freelists[nid])) {
> - page = list_entry(h->hugepage_freelists[nid].next,
> - struct page, lru);
> - list_del(&page->lru);
> - h->free_huge_pages--;
> - h->free_huge_pages_node[nid]--;
> -
> - if (!avoid_reserve)
> - decrement_hugepage_resv_vma(h, vma);
> -
> - break;
> + if (cpuset_zone_allowed_softwall(zone, htlb_alloc_mask)) {
> + page = dequeue_huge_page_node(h, zone_to_nid(zone));
> + if (page) {
> + if (!avoid_reserve)
> + decrement_hugepage_resv_vma(h, vma);
> + break;
> + }
> }
> }

This looks functionally equivalent so no problems there.

> err:
> @@ -770,11 +776,10 @@ static int free_pool_huge_page(struct hstate *h, nodemask_t *nodes_allowed,
> return ret;
> }
>
> -static struct page *alloc_buddy_huge_page(struct hstate *h,
> - struct vm_area_struct *vma, unsigned long address)
> +static struct page *alloc_buddy_huge_page(struct hstate *h, int nid)
> {
> struct page *page;
> - unsigned int nid;
> + unsigned int r_nid;
>

Why the rename, just to avoid changing the value of a function parameter?

> if (h->order >= MAX_ORDER)
> return NULL;
> @@ -812,9 +817,14 @@ static struct page *alloc_buddy_huge_page(struct hstate *h,
> }
> spin_unlock(&hugetlb_lock);
>
> - page = alloc_pages(htlb_alloc_mask|__GFP_COMP|
> - __GFP_REPEAT|__GFP_NOWARN,
> - huge_page_order(h));
> + if (nid == NUMA_NO_NODE)
> + page = alloc_pages(htlb_alloc_mask|__GFP_COMP|
> + __GFP_REPEAT|__GFP_NOWARN,
> + huge_page_order(h));
> + else
> + page = alloc_pages_exact_node(nid,
> + htlb_alloc_mask|__GFP_COMP|__GFP_THISNODE|
> + __GFP_REPEAT|__GFP_NOWARN, huge_page_order(h));
>

Why not just call alloc_pages_node()?

> if (page && arch_prepare_hugepage(page)) {
> __free_pages(page, huge_page_order(h));
> @@ -829,13 +839,13 @@ static struct page *alloc_buddy_huge_page(struct hstate *h,
> */
> put_page_testzero(page);
> VM_BUG_ON(page_count(page));
> - nid = page_to_nid(page);
> + r_nid = page_to_nid(page);
> set_compound_page_dtor(page, free_huge_page);
> /*
> * We incremented the global counters already
> */
> - h->nr_huge_pages_node[nid]++;
> - h->surplus_huge_pages_node[nid]++;
> + h->nr_huge_pages_node[r_nid]++;
> + h->surplus_huge_pages_node[r_nid]++;
> __count_vm_event(HTLB_BUDDY_PGALLOC);
> } else {
> h->nr_huge_pages--;
> @@ -848,6 +858,25 @@ static struct page *alloc_buddy_huge_page(struct hstate *h,
> }
>
> /*
> + * This allocation function is useful in the context where vma is irrelevant.
> + * E.g. soft-offlining uses this function because it only cares physical
> + * address of error page.
> + */
> +struct page *alloc_huge_page_node(struct hstate *h, int nid)
> +{
> + struct page *page;
> +
> + spin_lock(&hugetlb_lock);
> + page = dequeue_huge_page_node(h, nid);
> + spin_unlock(&hugetlb_lock);
> +
> + if (!page)
> + page = alloc_buddy_huge_page(h, nid);
> +
> + return page;
> +}
> +
> +/*
> * Increase the hugetlb pool such that it can accomodate a reservation
> * of size 'delta'.
> */
> @@ -871,7 +900,7 @@ static int gather_surplus_pages(struct hstate *h, int delta)
> retry:
> spin_unlock(&hugetlb_lock);
> for (i = 0; i < needed; i++) {
> - page = alloc_buddy_huge_page(h, NULL, 0);
> + page = alloc_buddy_huge_page(h, NUMA_NO_NODE);
> if (!page) {
> /*
> * We were not able to allocate enough pages to
> @@ -1052,7 +1081,7 @@ static struct page *alloc_huge_page(struct vm_area_struct *vma,
> spin_unlock(&hugetlb_lock);
>
> if (!page) {
> - page = alloc_buddy_huge_page(h, vma, addr);
> + page = alloc_buddy_huge_page(h, NUMA_NO_NODE);
> if (!page) {
> hugetlb_put_quota(inode->i_mapping, chg);
> return ERR_PTR(-VM_FAULT_SIGBUS);

Mostly it looks ok, the only snag I see is the why you didn't use
alloc_pages_node().

--
Mel Gorman
Part-time Phd Student Linux Technology Center
University of Limerick IBM Dublin Software Lab


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