There is no isolation mechanism for hugepages so a hugepage that
is migrated is returned to its hugepage freelist. This creates
problems for alloc_contig_range() because migrated hugepages can
be allocated as migrate targets for subsequent hugepage migration
attempts.
Even if the migration succeeds the alloc_contig_range() attempt
will fail because test_pages_isolated() will find the now free
hugepages haven't been dissolved.
A subsequent attempt by alloc_contig_range() is necessary for the
isolate_migratepages_range() function to find the freed hugepage
and dissolve it (assuming it has not been reallocated).
A workqueue is introduced to perform the equivalent functionality
of alloc_and_dissolve_huge_page() for a migrated hugepage when it
is freed so that the pages can be released to the isolated page
lists of the buddy allocator allowing the alloc_contig_range()
attempt to succeed.
The HPG_dissolve hugepage flag is introduced to allow tagging
migratable hugepages that should be dissolved when freed.
Signed-off-by: Doug Berger <opendmb@xxxxxxxxx>
---
include/linux/hugetlb.h | 5 +++
mm/hugetlb.c | 72 ++++++++++++++++++++++++++++++++++++++---
mm/migrate.c | 1 +
mm/page_alloc.c | 1 +
4 files changed, 75 insertions(+), 4 deletions(-)
diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 3ec981a0d8b3..0e6e21805e51 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -222,6 +222,7 @@ unsigned long hugetlb_change_protection(struct vm_area_struct *vma,
bool is_hugetlb_entry_migration(pte_t pte);
void hugetlb_unshare_all_pmds(struct vm_area_struct *vma);
+void sync_hugetlb_dissolve(void);
#else /* !CONFIG_HUGETLB_PAGE */
@@ -430,6 +431,8 @@ static inline vm_fault_t hugetlb_fault(struct mm_struct *mm,
static inline void hugetlb_unshare_all_pmds(struct vm_area_struct *vma) { }
+static inline void sync_hugetlb_dissolve(void) { }
+
#endif /* !CONFIG_HUGETLB_PAGE */
/*
* hugepages at page global directory. If arch support
@@ -574,6 +577,7 @@ enum hugetlb_page_flags {
HPG_freed,
HPG_vmemmap_optimized,
HPG_raw_hwp_unreliable,
+ HPG_dissolve,
__NR_HPAGEFLAGS,
};
@@ -621,6 +625,7 @@ HPAGEFLAG(Temporary, temporary)
HPAGEFLAG(Freed, freed)
HPAGEFLAG(VmemmapOptimized, vmemmap_optimized)
HPAGEFLAG(RawHwpUnreliable, raw_hwp_unreliable)
+HPAGEFLAG(Dissolve, dissolve)
#ifdef CONFIG_HUGETLB_PAGE
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 2b60de78007c..eab812760fbe 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1582,6 +1582,10 @@ static void __update_and_free_page(struct hstate *h, struct page *page)
}
}
+static LLIST_HEAD(hpage_dissolvelist);
+static void dissolve_hpage_workfn(struct work_struct *work);
+static DECLARE_WORK(dissolve_hpage_work, dissolve_hpage_workfn);
+
/*
* As update_and_free_page() can be called under any context, so we cannot
* use GFP_KERNEL to allocate vmemmap pages. However, we can defer the
@@ -1628,6 +1632,8 @@ static inline void flush_free_hpage_work(struct hstate *h)
{
if (hugetlb_vmemmap_optimizable(h))
flush_work(&free_hpage_work);
+ if (!hstate_is_gigantic(h))
+ flush_work(&dissolve_hpage_work);
}
static void update_and_free_page(struct hstate *h, struct page *page,
@@ -1679,7 +1685,7 @@ void free_huge_page(struct page *page)
struct hstate *h = page_hstate(page);
int nid = page_to_nid(page);
struct hugepage_subpool *spool = hugetlb_page_subpool(page);
- bool restore_reserve;
+ bool restore_reserve, dissolve;
unsigned long flags;
VM_BUG_ON_PAGE(page_count(page), page);
@@ -1691,6 +1697,8 @@ void free_huge_page(struct page *page)
page->mapping = NULL;
restore_reserve = HPageRestoreReserve(page);
ClearHPageRestoreReserve(page);
+ dissolve = HPageDissolve(page);
+ ClearHPageDissolve(page);
/*
* If HPageRestoreReserve was set on page, page allocation consumed a
@@ -1729,6 +1737,11 @@ void free_huge_page(struct page *page)
remove_hugetlb_page(h, page, true);
spin_unlock_irqrestore(&hugetlb_lock, flags);
update_and_free_page(h, page, true);
+ } else if (dissolve) {
+ spin_unlock_irqrestore(&hugetlb_lock, flags);
+ if (llist_add((struct llist_node *)&page->mapping,
+ &hpage_dissolvelist))
+ schedule_work(&dissolve_hpage_work);
} else {
arch_clear_hugepage_flags(page);
enqueue_huge_page(h, page);
@@ -2771,6 +2784,49 @@ static void replace_hugepage(struct hstate *h, int nid, struct page *old_page,
enqueue_huge_page(h, new_page);
}
+static void dissolve_hpage_workfn(struct work_struct *work)
+{
+ struct llist_node *node;
+
+ node = llist_del_all(&hpage_dissolvelist);
+
+ while (node) {
+ struct page *oldpage, *newpage;
+ struct hstate *h;
+ int nid;
+
+ oldpage = container_of((struct address_space **)node,
+ struct page, mapping);
+ node = node->next;
+ oldpage->mapping = NULL;
+
+ h = page_hstate(oldpage);
+ nid = page_to_nid(oldpage);
+
+ newpage = alloc_replacement_page(h, nid);
+
+ spin_lock_irq(&hugetlb_lock);
+ /* finish freeing oldpage */
+ arch_clear_hugepage_flags(oldpage);
+ enqueue_huge_page(h, oldpage);
+ if (IS_ERR(newpage)) {
+ /* cannot dissolve so just leave free */
+ spin_unlock_irq(&hugetlb_lock);
+ goto next;
+ }
+
+ replace_hugepage(h, nid, oldpage, newpage);
+
+ /*
+ * Pages have been replaced, we can safely free the old one.
+ */
+ spin_unlock_irq(&hugetlb_lock);
+ __update_and_free_page(h, oldpage);
+next:
+ cond_resched();
+ }
+}
+
/*
* alloc_and_dissolve_huge_page - Allocate a new page and dissolve the old one
* @h: struct hstate old page belongs to
@@ -2803,6 +2859,7 @@ static int alloc_and_dissolve_huge_page(struct hstate *h, struct page *old_page,
*/
spin_unlock_irq(&hugetlb_lock);
ret = isolate_hugetlb(old_page, list);
+ SetHPageDissolve(old_page);
spin_lock_irq(&hugetlb_lock);
goto free_new;
} else if (!HPageFreed(old_page)) {
@@ -2864,14 +2921,21 @@ int isolate_or_dissolve_huge_page(struct page *page, struct list_head *list)
if (hstate_is_gigantic(h))
return -ENOMEM;
- if (page_count(head) && !isolate_hugetlb(head, list))
+ if (page_count(head) && !isolate_hugetlb(head, list)) {
+ SetHPageDissolve(head);
ret = 0;
- else if (!page_count(head))
+ } else if (!page_count(head)) {
ret = alloc_and_dissolve_huge_page(h, head, list);
-
+ }
return ret;
}
+void sync_hugetlb_dissolve(void)
+{
+ flush_work(&free_hpage_work);
+ flush_work(&dissolve_hpage_work);
+}
+
struct page *alloc_huge_page(struct vm_area_struct *vma,
unsigned long addr, int avoid_reserve)
{
diff --git a/mm/migrate.c b/mm/migrate.c
index 6a1597c92261..b6c6123e614c 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -141,6 +141,7 @@ void putback_movable_pages(struct list_head *l)
list_for_each_entry_safe(page, page2, l, lru) {
if (unlikely(PageHuge(page))) {
+ ClearHPageDissolve(page);
putback_active_hugepage(page);
continue;
}
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index e5486d47406e..6bf76bbc0308 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -9235,6 +9235,7 @@ int alloc_contig_range(unsigned long start, unsigned long end,
if (ret && ret != -EBUSY)
goto done;
ret = 0;
+ sync_hugetlb_dissolve();
/*
* Pages from [start, end) are within a pageblock_nr_pages
--
2.25.1
