When we free a HugeTLB page to the buddy allocator, we need to allocate
the vmemmap pages associated with it. However, we may not be able to
allocate the vmemmap pages when the system is under memory pressure. In
this case, we just refuse to free the HugeTLB page. This changes behavior
in some corner cases as listed below:
1) Failing to free a huge page triggered by the user (decrease nr_pages).
User needs to try again later.
2) Failing to free a surplus huge page when freed by the application.
Try again later when freeing a huge page next time.
3) Failing to dissolve a free huge page on ZONE_MOVABLE via
offline_pages().
This can happen when we have plenty of ZONE_MOVABLE memory, but
not enough kernel memory to allocate vmemmmap pages. We may even
be able to migrate huge page contents, but will not be able to
dissolve the source huge page. This will prevent an offline
operation and is unfortunate as memory offlining is expected to
succeed on movable zones. Users that depend on memory hotplug
to succeed for movable zones should carefully consider whether the
memory savings gained from this feature are worth the risk of
possibly not being able to offline memory in certain situations.
4) Failing to dissolve a huge page on CMA/ZONE_MOVABLE via
alloc_contig_range() - once we have that handling in place. Mainly
affects CMA and virtio-mem.
Similar to 3). virito-mem will handle migration errors gracefully.
CMA might be able to fallback on other free areas within the CMA
region.
Vmemmap pages are allocated from the page freeing context. In order for
those allocations to be not disruptive (e.g. trigger oom killer)
__GFP_NORETRY is used. hugetlb_lock is dropped for the allocation
because a non sleeping allocation would be too fragile and it could fail
too easily under memory pressure. GFP_ATOMIC or other modes to access
memory reserves is not used because we want to prevent consuming
reserves under heavy hugetlb freeing.
Signed-off-by: Muchun Song <songmuc...@bytedance.com>
Tested-by: Chen Huang <chenhua...@huawei.com>
Tested-by: Bodeddula Balasubramaniam <boded...@amazon.com>
---
Documentation/admin-guide/mm/hugetlbpage.rst | 8 +++
include/linux/mm.h | 2 +
mm/hugetlb.c | 92 +++++++++++++++++++++-------
mm/hugetlb_vmemmap.c | 32 ++++++----
mm/hugetlb_vmemmap.h | 23 +++++++
mm/sparse-vmemmap.c | 75 ++++++++++++++++++++++-
6 files changed, 197 insertions(+), 35 deletions(-)
diff --git a/Documentation/admin-guide/mm/hugetlbpage.rst
b/Documentation/admin-guide/mm/hugetlbpage.rst
index f7b1c7462991..6988895d09a8 100644
--- a/Documentation/admin-guide/mm/hugetlbpage.rst
+++ b/Documentation/admin-guide/mm/hugetlbpage.rst
@@ -60,6 +60,10 @@ HugePages_Surp
the pool above the value in ``/proc/sys/vm/nr_hugepages``. The
maximum number of surplus huge pages is controlled by
``/proc/sys/vm/nr_overcommit_hugepages``.
+ Note: When the feature of freeing unused vmemmap pages associated
+ with each hugetlb page is enabled, the number of surplus huge pages
+ may be temporarily larger than the maximum number of surplus huge
+ pages when the system is under memory pressure.
Hugepagesize
is the default hugepage size (in Kb).
Hugetlb
@@ -80,6 +84,10 @@ returned to the huge page pool when freed by a task. A user
with root
privileges can dynamically allocate more or free some persistent huge pages
by increasing or decreasing the value of ``nr_hugepages``.
+Note: When the feature of freeing unused vmemmap pages associated with each
+hugetlb page is enabled, we can fail to free the huge pages triggered by
+the user when ths system is under memory pressure. Please try again later.
+
Pages that are used as huge pages are reserved inside the kernel and cannot
be used for other purposes. Huge pages cannot be swapped out under
memory pressure.
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 4ddfc31f21c6..77693c944a36 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2973,6 +2973,8 @@ static inline void print_vma_addr(char *prefix, unsigned
long rip)
void vmemmap_remap_free(unsigned long start, unsigned long end,
unsigned long reuse);
+int vmemmap_remap_alloc(unsigned long start, unsigned long end,
+ unsigned long reuse, gfp_t gfp_mask);
void *sparse_buffer_alloc(unsigned long size);
struct page * __populate_section_memmap(unsigned long pfn,
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 43fed6785322..377e0c1b283f 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1304,16 +1304,59 @@ static inline void
destroy_compound_gigantic_page(struct page *page,
unsigned int order) { }
#endif
-static void update_and_free_page(struct hstate *h, struct page *page)
+static int update_and_free_page(struct hstate *h, struct page *page)
+ __releases(&hugetlb_lock) __acquires(&hugetlb_lock)
{
int i;
struct page *subpage = page;
+ int nid = page_to_nid(page);
if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported())
- return;
+ return 0;
h->nr_huge_pages--;
- h->nr_huge_pages_node[page_to_nid(page)]--;
+ h->nr_huge_pages_node[nid]--;
+ VM_BUG_ON_PAGE(hugetlb_cgroup_from_page(page), page);
+ VM_BUG_ON_PAGE(hugetlb_cgroup_from_page_rsvd(page), page);
+ set_page_refcounted(page);
+ set_compound_page_dtor(page, NULL_COMPOUND_DTOR);
+
+ /*
+ * If the vmemmap pages associated with the HugeTLB page can be
+ * optimized or the page is gigantic, we might block in
+ * alloc_huge_page_vmemmap() or free_gigantic_page(). In both
+ * cases, drop the hugetlb_lock.
+ */
+ if (free_vmemmap_pages_per_hpage(h) || hstate_is_gigantic(h))
+ spin_unlock(&hugetlb_lock);
+
+ if (alloc_huge_page_vmemmap(h, page)) {
+ spin_lock(&hugetlb_lock);
+ INIT_LIST_HEAD(&page->lru);
+ set_compound_page_dtor(page, HUGETLB_PAGE_DTOR);
+ h->nr_huge_pages++;
+ h->nr_huge_pages_node[nid]++;
+
+ /*
+ * If we cannot allocate vmemmap pages, just refuse to free the
+ * page and put the page back on the hugetlb free list and treat
+ * as a surplus page.
+ */
+ h->surplus_huge_pages++;
+ h->surplus_huge_pages_node[nid]++;
+
+ /*
+ * The refcount can possibly be increased by memory-failure or
+ * soft_offline handlers.
+ */
+ if (likely(put_page_testzero(page))) {
+ arch_clear_hugepage_flags(page);
+ enqueue_huge_page(h, page);
+ }
+
+ return -ENOMEM;
+ }
+
for (i = 0; i < pages_per_huge_page(h);
i++, subpage = mem_map_next(subpage, page, i)) {
subpage->flags &= ~(1 << PG_locked | 1 << PG_error |
@@ -1321,22 +1364,18 @@ static void update_and_free_page(struct hstate *h,
struct page *page)
1 << PG_active | 1 << PG_private |
1 << PG_writeback);
}
- VM_BUG_ON_PAGE(hugetlb_cgroup_from_page(page), page);
- VM_BUG_ON_PAGE(hugetlb_cgroup_from_page_rsvd(page), page);
- set_compound_page_dtor(page, NULL_COMPOUND_DTOR);
- set_page_refcounted(page);
+
if (hstate_is_gigantic(h)) {
- /*
- * Temporarily drop the hugetlb_lock, because
- * we might block in free_gigantic_page().
- */
- spin_unlock(&hugetlb_lock);
destroy_compound_gigantic_page(page, huge_page_order(h));
free_gigantic_page(page, huge_page_order(h));
- spin_lock(&hugetlb_lock);
} else {
__free_pages(page, huge_page_order(h));
}
+
+ if (free_vmemmap_pages_per_hpage(h) || hstate_is_gigantic(h))
+ spin_lock(&hugetlb_lock);
+
+ return 0;
}
struct hstate *size_to_hstate(unsigned long size)
@@ -1404,9 +1443,9 @@ static void __free_huge_page(struct page *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);
h->surplus_huge_pages--;
h->surplus_huge_pages_node[nid]--;
+ update_and_free_page(h, page);
} else {
arch_clear_hugepage_flags(page);
enqueue_huge_page(h, page);
@@ -1447,7 +1486,7 @@ void free_huge_page(struct page *page)
/*
* Defer freeing if in non-task context to avoid hugetlb_lock deadlock.
*/
- if (!in_task()) {
+ if (in_atomic()) {
/*
* Only call schedule_work() if hpage_freelist is previously
* empty. Otherwise, schedule_work() had been called but the
@@ -1699,8 +1738,7 @@ static int free_pool_huge_page(struct hstate *h,
nodemask_t *nodes_allowed,
h->surplus_huge_pages--;
h->surplus_huge_pages_node[node]--;
}
- update_and_free_page(h, page);
- ret = 1;
+ ret = !update_and_free_page(h, page);
break;
}
}
@@ -1713,10 +1751,14 @@ static int free_pool_huge_page(struct hstate *h,
nodemask_t *nodes_allowed,
* nothing for in-use hugepages and non-hugepages.
* This function returns values like below:
*
- * -EBUSY: failed to dissolved free hugepages or the hugepage is in-use
- * (allocated or reserved.)
- * 0: successfully dissolved free hugepages or the page is not a
- * hugepage (considered as already dissolved)
+ * -ENOMEM: failed to allocate vmemmap pages to free the freed hugepages
+ * when the system is under memory pressure and the feature of
+ * freeing unused vmemmap pages associated with each hugetlb page
+ * is enabled.
+ * -EBUSY: failed to dissolved free hugepages or the hugepage is in-use
+ * (allocated or reserved.)
+ * 0: successfully dissolved free hugepages or the page is not a
+ * hugepage (considered as already dissolved)
*/
int dissolve_free_huge_page(struct page *page)
{
@@ -1771,8 +1813,12 @@ int dissolve_free_huge_page(struct page *page)
h->free_huge_pages--;
h->free_huge_pages_node[nid]--;
h->max_huge_pages--;
- update_and_free_page(h, head);
- rc = 0;
+ rc = update_and_free_page(h, head);
+ if (rc) {
+ h->surplus_huge_pages--;
+ h->surplus_huge_pages_node[nid]--;
+ h->max_huge_pages++;
+ }
}
out:
spin_unlock(&hugetlb_lock);
diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
index 0209b736e0b4..f7ab3d99250a 100644
--- a/mm/hugetlb_vmemmap.c
+++ b/mm/hugetlb_vmemmap.c
@@ -181,21 +181,31 @@
#define RESERVE_VMEMMAP_NR 2U
#define RESERVE_VMEMMAP_SIZE (RESERVE_VMEMMAP_NR << PAGE_SHIFT)
-/*
- * How many vmemmap pages associated with a HugeTLB page that can be freed
- * to the buddy allocator.
- *
- * Todo: Returns zero for now, which means the feature is disabled. We will
- * enable it once all the infrastructure is there.
- */
-static inline unsigned int free_vmemmap_pages_per_hpage(struct hstate *h)
+static inline unsigned long free_vmemmap_pages_size_per_hpage(struct hstate *h)
{
- return 0;
+ return (unsigned long)free_vmemmap_pages_per_hpage(h) << PAGE_SHIFT;
}
-static inline unsigned long free_vmemmap_pages_size_per_hpage(struct hstate *h)
+int alloc_huge_page_vmemmap(struct hstate *h, struct page *head)
{
- return (unsigned long)free_vmemmap_pages_per_hpage(h) << PAGE_SHIFT;
+ unsigned long vmemmap_addr = (unsigned long)head;
+ unsigned long vmemmap_end, vmemmap_reuse;
+
+ if (!free_vmemmap_pages_per_hpage(h))
+ return 0;
+
+ vmemmap_addr += RESERVE_VMEMMAP_SIZE;
+ vmemmap_end = vmemmap_addr + free_vmemmap_pages_size_per_hpage(h);
+ vmemmap_reuse = vmemmap_addr - PAGE_SIZE;
+ /*
+ * The pages which the vmemmap virtual address range [@vmemmap_addr,
+ * @vmemmap_end) are mapped to are freed to the buddy allocator, and
+ * the range is mapped to the page which @vmemmap_reuse is mapped to.
+ * When a HugeTLB page is freed to the buddy allocator, previously
+ * discarded vmemmap pages must be allocated and remapping.
+ */
+ return vmemmap_remap_alloc(vmemmap_addr, vmemmap_end, vmemmap_reuse,
+ GFP_KERNEL | __GFP_NORETRY | __GFP_THISNODE);
}
void free_huge_page_vmemmap(struct hstate *h, struct page *head)
diff --git a/mm/hugetlb_vmemmap.h b/mm/hugetlb_vmemmap.h
index 6923f03534d5..a37771b0b82a 100644
--- a/mm/hugetlb_vmemmap.h
+++ b/mm/hugetlb_vmemmap.h
@@ -11,10 +11,33 @@
#include <linux/hugetlb.h>
#ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
+int alloc_huge_page_vmemmap(struct hstate *h, struct page *head);
void free_huge_page_vmemmap(struct hstate *h, struct page *head);
+
+/*
+ * How many vmemmap pages associated with a HugeTLB page that can be freed
+ * to the buddy allocator.
+ *
+ * Todo: Returns zero for now, which means the feature is disabled. We will
+ * enable it once all the infrastructure is there.
+ */
+static inline unsigned int free_vmemmap_pages_per_hpage(struct hstate *h)
+{
+ return 0;
+}
#else
+static inline int alloc_huge_page_vmemmap(struct hstate *h, struct page *head)
+{
+ return 0;
+}
+
static inline void free_huge_page_vmemmap(struct hstate *h, struct page *head)
{
}
+
+static inline unsigned int free_vmemmap_pages_per_hpage(struct hstate *h)
+{
+ return 0;
+}
#endif /* CONFIG_HUGETLB_PAGE_FREE_VMEMMAP */
#endif /* _LINUX_HUGETLB_VMEMMAP_H */
diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
index d3076a7a3783..60fc6cd6cd23 100644
--- a/mm/sparse-vmemmap.c
+++ b/mm/sparse-vmemmap.c
@@ -40,7 +40,8 @@
* @remap_pte: called for each lowest-level entry (PTE).
* @reuse_page: the page which is reused for the tail vmemmap
pages.
* @reuse_addr: the virtual address of the @reuse_page page.
- * @vmemmap_pages: the list head of the vmemmap pages that can be freed.
+ * @vmemmap_pages: the list head of the vmemmap pages that can be freed
+ * or is mapped from.
*/
struct vmemmap_remap_walk {
void (*remap_pte)(pte_t *pte, unsigned long addr,
@@ -237,6 +238,78 @@ void vmemmap_remap_free(unsigned long start, unsigned long
end,
free_vmemmap_page_list(&vmemmap_pages);
}
+static void vmemmap_restore_pte(pte_t *pte, unsigned long addr,
+ struct vmemmap_remap_walk *walk)
+{
+ pgprot_t pgprot = PAGE_KERNEL;
+ struct page *page;
+ void *to;
+
+ BUG_ON(pte_page(*pte) != walk->reuse_page);
+
+ page = list_first_entry(walk->vmemmap_pages, struct page, lru);
+ list_del(&page->lru);
+ to = page_to_virt(page);
+ copy_page(to, (void *)walk->reuse_addr);
+
+ set_pte_at(&init_mm, addr, pte, mk_pte(page, pgprot));
+}
+
+static int alloc_vmemmap_page_list(unsigned long start, unsigned long end,
+ gfp_t gfp_mask, struct list_head *list)
+{
+ unsigned long nr_pages = (end - start) >> PAGE_SHIFT;
+ int nid = page_to_nid((struct page *)start);
+ struct page *page, *next;
+
+ while (nr_pages--) {
+ page = alloc_pages_node(nid, gfp_mask, 0);
+ if (!page)
+ goto out;
+ list_add_tail(&page->lru, list);
+ }
+
+ return 0;
+out:
+ list_for_each_entry_safe(page, next, list, lru)
+ __free_pages(page, 0);
+ return -ENOMEM;
+}
+
+/**
+ * vmemmap_remap_alloc - remap the vmemmap virtual address range [@start, end)
+ * to the page which is from the @vmemmap_pages
+ * respectively.
+ * @start: start address of the vmemmap virtual address range that we want
+ * to remap.
+ * @end: end address of the vmemmap virtual address range that we want to
+ * remap.
+ * @reuse: reuse address.
+ * @gpf_mask: GFP flag for allocating vmemmap pages.
+ */
+int vmemmap_remap_alloc(unsigned long start, unsigned long end,
+ unsigned long reuse, gfp_t gfp_mask)
+{
+ LIST_HEAD(vmemmap_pages);
+ struct vmemmap_remap_walk walk = {
+ .remap_pte = vmemmap_restore_pte,
+ .reuse_addr = reuse,
+ .vmemmap_pages = &vmemmap_pages,
+ };
+
+ /* See the comment in the vmemmap_remap_free(). */
+ BUG_ON(start - reuse != PAGE_SIZE);
+
+ might_sleep_if(gfpflags_allow_blocking(gfp_mask));
+
+ if (alloc_vmemmap_page_list(start, end, gfp_mask, &vmemmap_pages))
+ return -ENOMEM;
+
+ vmemmap_remap_range(reuse, end, &walk);
+
+ return 0;
+}
+
/*
* Allocate a block of memory to be used to back the virtual memory map
* or to back the page tables that are used to create the mapping.
--
2.11.0
