From ab5ac90aecf5685eb630c42c396f5f14726b0afd Mon Sep 17 00:00:00 2001 From: Michal Hocko Date: Wed, 31 Jan 2018 16:20:48 -0800 Subject: mm, hugetlb: do not rely on overcommit limit during migration hugepage migration relies on __alloc_buddy_huge_page to get a new page. This has 2 main disadvantages. 1) it doesn't allow to migrate any huge page if the pool is used completely which is not an exceptional case as the pool is static and unused memory is just wasted. 2) it leads to a weird semantic when migration between two numa nodes might increase the pool size of the destination NUMA node while the page is in use. The issue is caused by per NUMA node surplus pages tracking (see free_huge_page). Address both issues by changing the way how we allocate and account pages allocated for migration. Those should temporal by definition. So we mark them that way (we will abuse page flags in the 3rd page) and update free_huge_page to free such pages to the page allocator. Page migration path then just transfers the temporal status from the new page to the old one which will be freed on the last reference. The global surplus count will never change during this path but we still have to be careful when migrating a per-node suprlus page. This is now handled in move_hugetlb_state which is called from the migration path and it copies the hugetlb specific page state and fixes up the accounting when needed Rename __alloc_buddy_huge_page to __alloc_surplus_huge_page to better reflect its purpose. The new allocation routine for the migration path is __alloc_migrate_huge_page. The user visible effect of this patch is that migrated pages are really temporal and they travel between NUMA nodes as per the migration request: Before migration /sys/devices/system/node/node0/hugepages/hugepages-2048kB/free_hugepages:0 /sys/devices/system/node/node0/hugepages/hugepages-2048kB/nr_hugepages:1 /sys/devices/system/node/node0/hugepages/hugepages-2048kB/surplus_hugepages:0 /sys/devices/system/node/node1/hugepages/hugepages-2048kB/free_hugepages:0 /sys/devices/system/node/node1/hugepages/hugepages-2048kB/nr_hugepages:0 /sys/devices/system/node/node1/hugepages/hugepages-2048kB/surplus_hugepages:0 After /sys/devices/system/node/node0/hugepages/hugepages-2048kB/free_hugepages:0 /sys/devices/system/node/node0/hugepages/hugepages-2048kB/nr_hugepages:0 /sys/devices/system/node/node0/hugepages/hugepages-2048kB/surplus_hugepages:0 /sys/devices/system/node/node1/hugepages/hugepages-2048kB/free_hugepages:0 /sys/devices/system/node/node1/hugepages/hugepages-2048kB/nr_hugepages:1 /sys/devices/system/node/node1/hugepages/hugepages-2048kB/surplus_hugepages:0 with the previous implementation, both nodes would have nr_hugepages:1 until the page is freed. Link: http://lkml.kernel.org/r/20180103093213.26329-4-mhocko@kernel.org Signed-off-by: Michal Hocko Reviewed-by: Mike Kravetz Reviewed-by: Naoya Horiguchi Cc: Andrea Reale Cc: Anshuman Khandual Cc: Kirill A. Shutemov Cc: Vlastimil Babka Cc: Zi Yan Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/hugetlb.c | 111 ++++++++++++++++++++++++++++++++++++++++++++++++++--------- mm/migrate.c | 3 +- 2 files changed, 96 insertions(+), 18 deletions(-) (limited to 'mm') diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 360765156c7c..f260ffa26363 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -34,6 +34,7 @@ #include #include #include +#include #include "internal.h" int hugetlb_max_hstate __read_mostly; @@ -1219,6 +1220,28 @@ static void clear_page_huge_active(struct page *page) ClearPagePrivate(&page[1]); } +/* + * Internal hugetlb specific page flag. Do not use outside of the hugetlb + * code + */ +static inline bool PageHugeTemporary(struct page *page) +{ + if (!PageHuge(page)) + return false; + + return (unsigned long)page[2].mapping == -1U; +} + +static inline void SetPageHugeTemporary(struct page *page) +{ + page[2].mapping = (void *)-1U; +} + +static inline void ClearPageHugeTemporary(struct page *page) +{ + page[2].mapping = NULL; +} + void free_huge_page(struct page *page) { /* @@ -1253,7 +1276,11 @@ void free_huge_page(struct page *page) if (restore_reserve) h->resv_huge_pages++; - if (h->surplus_huge_pages_node[nid]) { + if (PageHugeTemporary(page)) { + list_del(&page->lru); + ClearPageHugeTemporary(page); + update_and_free_page(h, page); + } else if (h->surplus_huge_pages_node[nid]) { /* remove the page from active list */ list_del(&page->lru); update_and_free_page(h, page); @@ -1507,7 +1534,10 @@ int dissolve_free_huge_pages(unsigned long start_pfn, unsigned long end_pfn) return rc; } -static struct page *__alloc_buddy_huge_page(struct hstate *h, gfp_t gfp_mask, +/* + * Allocates a fresh surplus page from the page allocator. + */ +static struct page *__alloc_surplus_huge_page(struct hstate *h, gfp_t gfp_mask, int nid, nodemask_t *nmask) { struct page *page; @@ -1571,6 +1601,28 @@ static struct page *__alloc_buddy_huge_page(struct hstate *h, gfp_t gfp_mask, return page; } +static struct page *__alloc_migrate_huge_page(struct hstate *h, gfp_t gfp_mask, + int nid, nodemask_t *nmask) +{ + struct page *page; + + if (hstate_is_gigantic(h)) + return NULL; + + page = __hugetlb_alloc_buddy_huge_page(h, gfp_mask, nid, nmask); + if (!page) + return NULL; + + /* + * We do not account these pages as surplus because they are only + * temporary and will be released properly on the last reference + */ + prep_new_huge_page(h, page, page_to_nid(page)); + SetPageHugeTemporary(page); + + return page; +} + /* * Use the VMA's mpolicy to allocate a huge page from the buddy. */ @@ -1585,17 +1637,13 @@ struct page *__alloc_buddy_huge_page_with_mpol(struct hstate *h, nodemask_t *nodemask; nid = huge_node(vma, addr, gfp_mask, &mpol, &nodemask); - page = __alloc_buddy_huge_page(h, gfp_mask, nid, nodemask); + page = __alloc_surplus_huge_page(h, gfp_mask, nid, nodemask); mpol_cond_put(mpol); return page; } -/* - * 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. - */ +/* page migration callback function */ struct page *alloc_huge_page_node(struct hstate *h, int nid) { gfp_t gfp_mask = htlb_alloc_mask(h); @@ -1610,12 +1658,12 @@ struct page *alloc_huge_page_node(struct hstate *h, int nid) spin_unlock(&hugetlb_lock); if (!page) - page = __alloc_buddy_huge_page(h, gfp_mask, nid, NULL); + page = __alloc_migrate_huge_page(h, gfp_mask, nid, NULL); return page; } - +/* page migration callback function */ struct page *alloc_huge_page_nodemask(struct hstate *h, int preferred_nid, nodemask_t *nmask) { @@ -1633,9 +1681,7 @@ struct page *alloc_huge_page_nodemask(struct hstate *h, int preferred_nid, } spin_unlock(&hugetlb_lock); - /* No reservations, try to overcommit */ - - return __alloc_buddy_huge_page(h, gfp_mask, preferred_nid, nmask); + return __alloc_migrate_huge_page(h, gfp_mask, preferred_nid, nmask); } /* @@ -1663,7 +1709,7 @@ 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, htlb_alloc_mask(h), + page = __alloc_surplus_huge_page(h, htlb_alloc_mask(h), NUMA_NO_NODE, NULL); if (!page) { alloc_ok = false; @@ -2260,7 +2306,7 @@ static unsigned long set_max_huge_pages(struct hstate *h, unsigned long count, * First take pages out of surplus state. Then make up the * remaining difference by allocating fresh huge pages. * - * We might race with __alloc_buddy_huge_page() here and be unable + * We might race with __alloc_surplus_huge_page() here and be unable * to convert a surplus huge page to a normal huge page. That is * not critical, though, it just means the overall size of the * pool might be one hugepage larger than it needs to be, but @@ -2303,7 +2349,7 @@ static unsigned long set_max_huge_pages(struct hstate *h, unsigned long count, * By placing pages into the surplus state independent of the * overcommit value, we are allowing the surplus pool size to * exceed overcommit. There are few sane options here. Since - * __alloc_buddy_huge_page() is checking the global counter, + * __alloc_surplus_huge_page() is checking the global counter, * though, we'll note that we're not allowed to exceed surplus * and won't grow the pool anywhere else. Not until one of the * sysctls are changed, or the surplus pages go out of use. @@ -4779,3 +4825,36 @@ void putback_active_hugepage(struct page *page) spin_unlock(&hugetlb_lock); put_page(page); } + +void move_hugetlb_state(struct page *oldpage, struct page *newpage, int reason) +{ + struct hstate *h = page_hstate(oldpage); + + hugetlb_cgroup_migrate(oldpage, newpage); + set_page_owner_migrate_reason(newpage, reason); + + /* + * transfer temporary state of the new huge page. This is + * reverse to other transitions because the newpage is going to + * be final while the old one will be freed so it takes over + * the temporary status. + * + * Also note that we have to transfer the per-node surplus state + * here as well otherwise the global surplus count will not match + * the per-node's. + */ + if (PageHugeTemporary(newpage)) { + int old_nid = page_to_nid(oldpage); + int new_nid = page_to_nid(newpage); + + SetPageHugeTemporary(oldpage); + ClearPageHugeTemporary(newpage); + + spin_lock(&hugetlb_lock); + if (h->surplus_huge_pages_node[old_nid]) { + h->surplus_huge_pages_node[old_nid]--; + h->surplus_huge_pages_node[new_nid]++; + } + spin_unlock(&hugetlb_lock); + } +} diff --git a/mm/migrate.c b/mm/migrate.c index 4d0be47a322a..1e5525a25691 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -1323,9 +1323,8 @@ put_anon: put_anon_vma(anon_vma); if (rc == MIGRATEPAGE_SUCCESS) { - hugetlb_cgroup_migrate(hpage, new_hpage); + move_hugetlb_state(hpage, new_hpage, reason); put_new_page = NULL; - set_page_owner_migrate_reason(new_hpage, reason); } unlock_page(hpage); -- cgit v1.2.3