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SubjectRe: [PATCH 5/5] hugetlb: add support for gigantic page allocation at runtime
(2014/04/09 4:02), Luiz Capitulino wrote:
> HugeTLB is limited to allocating hugepages whose size are less than
> MAX_ORDER order. This is so because HugeTLB allocates hugepages via
> the buddy allocator. Gigantic pages (that is, pages whose size is
> greater than MAX_ORDER order) have to be allocated at boottime.
>
> However, boottime allocation has at least two serious problems. First,
> it doesn't support NUMA and second, gigantic pages allocated at
> boottime can't be freed.
>
> This commit solves both issues by adding support for allocating gigantic
> pages during runtime. It works just like regular sized hugepages,
> meaning that the interface in sysfs is the same, it supports NUMA,
> and gigantic pages can be freed.
>
> For example, on x86_64 gigantic pages are 1GB big. To allocate two 1G
> gigantic pages on node 1, one can do:
>
> # echo 2 > \
> /sys/devices/system/node/node1/hugepages/hugepages-1048576kB/nr_hugepages
>
> And to free them all:
>
> # echo 0 > \
> /sys/devices/system/node/node1/hugepages/hugepages-1048576kB/nr_hugepages
>
> The one problem with gigantic page allocation at runtime is that it
> can't be serviced by the buddy allocator. To overcome that problem, this
> commit scans all zones from a node looking for a large enough contiguous
> region. When one is found, it's allocated by using CMA, that is, we call
> alloc_contig_range() to do the actual allocation. For example, on x86_64
> we scan all zones looking for a 1GB contiguous region. When one is found,
> it's allocated by alloc_contig_range().
>
> One expected issue with that approach is that such gigantic contiguous
> regions tend to vanish as runtime goes by. The best way to avoid this for
> now is to make gigantic page allocations very early during system boot, say
> from a init script. Other possible optimization include using compaction,
> which is supported by CMA but is not explicitly used by this commit.
>
> It's also important to note the following:
>
> 1. Gigantic pages allocated at boottime by the hugepages= command-line
> option can be freed at runtime just fine
>
> 2. This commit adds support for gigantic pages only to x86_64. The
> reason is that I don't have access to nor experience with other archs.
> The code is arch indepedent though, so it should be simple to add
> support to different archs
>
> 3. I didn't add support for hugepage overcommit, that is allocating
> a gigantic page on demand when
> /proc/sys/vm/nr_overcommit_hugepages > 0. The reason is that I don't
> think it's reasonable to do the hard and long work required for
> allocating a gigantic page at fault time. But it should be simple
> to add this if wanted
>
> Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
> ---
> mm/hugetlb.c | 158 ++++++++++++++++++++++++++++++++++++++++++++++++++++++-----
> 1 file changed, 147 insertions(+), 11 deletions(-)
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 9dded98..2258045 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -679,11 +679,141 @@ static int hstate_next_node_to_free(struct hstate *h, nodemask_t *nodes_allowed)
> ((node = hstate_next_node_to_free(hs, mask)) || 1); \
> nr_nodes--)
>
> +#if defined(CONFIG_CMA) && defined(CONFIG_X86_64)
> +static void destroy_compound_gigantic_page(struct page *page,
> + unsigned long order)
> +{
> + int i;
> + int nr_pages = 1 << order;
> + struct page *p = page + 1;
> +
> + for (i = 1; i < nr_pages; i++, p = mem_map_next(p, page, i)) {
> + __ClearPageTail(p);
> + set_page_refcounted(p);
> + p->first_page = NULL;
> + }
> +
> + set_compound_order(page, 0);
> + __ClearPageHead(page);
> +}
> +
> +static void free_gigantic_page(struct page *page, unsigned order)
> +{
> + free_contig_range(page_to_pfn(page), 1 << order);
> +}
> +
> +static int __alloc_gigantic_page(unsigned long start_pfn, unsigned long count)
> +{
> + unsigned long end_pfn = start_pfn + count;
> + return alloc_contig_range(start_pfn, end_pfn, MIGRATE_MOVABLE);
> +}
> +
> +static bool pfn_range_valid_gigantic(unsigned long start_pfn,
> + unsigned long nr_pages)
> +{
> + unsigned long i, end_pfn = start_pfn + nr_pages;
> + struct page *page;
> +
> + for (i = start_pfn; i < end_pfn; i++) {
> + if (!pfn_valid(i))
> + return false;
> +
> + page = pfn_to_page(i);
> +
> + if (PageReserved(page))
> + return false;
> +
> + if (page_count(page) > 0)
> + return false;
> +
> + if (PageHuge(page))
> + return false;
> + }
> +
> + return true;
> +}
> +
> +static struct page *alloc_gigantic_page(int nid, unsigned order)
> +{
> + unsigned long nr_pages = 1 << order;
> + unsigned long ret, pfn, flags;
> + struct zone *z;
> +
> + z = NODE_DATA(nid)->node_zones;
> + for (; z - NODE_DATA(nid)->node_zones < MAX_NR_ZONES; z++) {
> + spin_lock_irqsave(&z->lock, flags);
> +
> + pfn = ALIGN(z->zone_start_pfn, nr_pages);
> + for (; pfn < zone_end_pfn(z); pfn += nr_pages) {

> + if (pfn_range_valid_gigantic(pfn, nr_pages)) {

How about it. It can reduce the indentation level.
if (!pfn_range_valid_gigantic(...))
continue;

And I think following check is necessary:
if (pfn + nr_pages >= zone_end_pfn(z))
break;
Thanks,
Yasuaki Ishimatsu

> + /*
> + * We release the zone lock here because
> + * alloc_contig_range() will also lock the zone
> + * at some point. If there's an allocation
> + * spinning on this lock, it may win the race
> + * and cause alloc_contig_range() to fail...
> + */
> + spin_unlock_irqrestore(&z->lock, flags);
> + ret = __alloc_gigantic_page(pfn, nr_pages);
> + if (!ret)
> + return pfn_to_page(pfn);
> + spin_lock_irqsave(&z->lock, flags);
> + }
> + }
> +
> + spin_unlock_irqrestore(&z->lock, flags);
> + }
> +
> + return NULL;
> +}
> +
> +static void prep_new_huge_page(struct hstate *h, struct page *page, int nid);
> +static void prep_compound_gigantic_page(struct page *page, unsigned long order);
> +
> +static struct page *alloc_fresh_gigantic_page_node(struct hstate *h, int nid)
> +{
> + struct page *page;
> +
> + page = alloc_gigantic_page(nid, huge_page_order(h));
> + if (page) {
> + prep_compound_gigantic_page(page, huge_page_order(h));
> + prep_new_huge_page(h, page, nid);
> + }
> +
> + return page;
> +}
> +
> +static int alloc_fresh_gigantic_page(struct hstate *h,
> + nodemask_t *nodes_allowed)
> +{
> + struct page *page = NULL;
> + int nr_nodes, node;
> +
> + for_each_node_mask_to_alloc(h, nr_nodes, node, nodes_allowed) {
> + page = alloc_fresh_gigantic_page_node(h, node);
> + if (page)
> + return 1;
> + }
> +
> + return 0;
> +}
> +
> +static inline bool gigantic_page_supported(void) { return true; }
> +#else
> +static inline bool gigantic_page_supported(void) { return false; }
> +static inline void free_gigantic_page(struct page *page, unsigned order) { }
> +static inline void destroy_compound_gigantic_page(struct page *page,
> + unsigned long order) { }
> +static inline int alloc_fresh_gigantic_page(struct hstate *h,
> + nodemask_t *nodes_allowed) { return 0; }
> +#endif
> +
> static void update_and_free_page(struct hstate *h, struct page *page)
> {
> int i;
>
> - VM_BUG_ON(hstate_is_gigantic(h));
> + if (hstate_is_gigantic(h) && !gigantic_page_supported())
> + return;
>
> h->nr_huge_pages--;
> h->nr_huge_pages_node[page_to_nid(page)]--;
> @@ -697,8 +827,13 @@ static void update_and_free_page(struct hstate *h, struct page *page)
> VM_BUG_ON_PAGE(hugetlb_cgroup_from_page(page), page);
> set_compound_page_dtor(page, NULL);
> set_page_refcounted(page);
> - arch_release_hugepage(page);
> - __free_pages(page, huge_page_order(h));
> + if (hstate_is_gigantic(h)) {
> + destroy_compound_gigantic_page(page, huge_page_order(h));
> + free_gigantic_page(page, huge_page_order(h));
> + } else {
> + arch_release_hugepage(page);
> + __free_pages(page, huge_page_order(h));
> + }
> }
>
> struct hstate *size_to_hstate(unsigned long size)
> @@ -737,7 +872,7 @@ static void free_huge_page(struct page *page)
> if (restore_reserve)
> h->resv_huge_pages++;
>
> - if (h->surplus_huge_pages_node[nid] && !hstate_is_gigantic(h)) {
> + if (h->surplus_huge_pages_node[nid]) {
> /* remove the page from active list */
> list_del(&page->lru);
> update_and_free_page(h, page);
> @@ -841,9 +976,6 @@ static struct page *alloc_fresh_huge_page_node(struct hstate *h, int nid)
> {
> struct page *page;
>
> - if (hstate_is_gigantic(h))
> - return NULL;
> -
> page = alloc_pages_exact_node(nid,
> htlb_alloc_mask(h)|__GFP_COMP|__GFP_THISNODE|
> __GFP_REPEAT|__GFP_NOWARN,
> @@ -1477,7 +1609,7 @@ static unsigned long set_max_huge_pages(struct hstate *h, unsigned long count,
> {
> unsigned long min_count, ret;
>
> - if (hstate_is_gigantic(h))
> + if (hstate_is_gigantic(h) && !gigantic_page_supported())
> return h->max_huge_pages;
>
> /*
> @@ -1504,7 +1636,11 @@ static unsigned long set_max_huge_pages(struct hstate *h, unsigned long count,
> * and reducing the surplus.
> */
> spin_unlock(&hugetlb_lock);
> - ret = alloc_fresh_huge_page(h, nodes_allowed);
> + if (hstate_is_gigantic(h)) {
> + ret = alloc_fresh_gigantic_page(h, nodes_allowed);
> + } else {
> + ret = alloc_fresh_huge_page(h, nodes_allowed);
> + }
> spin_lock(&hugetlb_lock);
> if (!ret)
> goto out;
> @@ -1603,7 +1739,7 @@ static ssize_t nr_hugepages_store_common(bool obey_mempolicy,
> goto out;
>
> h = kobj_to_hstate(kobj, &nid);
> - if (hstate_is_gigantic(h)) {
> + if (hstate_is_gigantic(h) && !gigantic_page_supported()) {
> err = -EINVAL;
> goto out;
> }
> @@ -2111,7 +2247,7 @@ static int hugetlb_sysctl_handler_common(bool obey_mempolicy,
>
> tmp = h->max_huge_pages;
>
> - if (write && hstate_is_gigantic(h))
> + if (write && hstate_is_gigantic(h) && !gigantic_page_supported())
> return -EINVAL;
>
> table->data = &tmp;
>




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