diff mbox series

[v21,6/9] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page

Message ID 20210425070752.17783-7-songmuchun@bytedance.com (mailing list archive)
State New
Headers show
Series Free some vmemmap pages of HugeTLB page | expand

Commit Message

Muchun Song April 25, 2021, 7:07 a.m. UTC
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 <songmuchun@bytedance.com>
---
 Documentation/admin-guide/mm/hugetlbpage.rst    |  8 ++
 Documentation/admin-guide/mm/memory-hotplug.rst | 13 ++++
 include/linux/hugetlb.h                         |  3 +
 include/linux/mm.h                              |  2 +
 mm/hugetlb.c                                    | 98 +++++++++++++++++++++----
 mm/hugetlb_vmemmap.c                            | 34 +++++++++
 mm/hugetlb_vmemmap.h                            |  6 ++
 mm/sparse-vmemmap.c                             | 75 ++++++++++++++++++-
 8 files changed, 223 insertions(+), 16 deletions(-)

Comments

Mike Kravetz April 29, 2021, 2:42 a.m. UTC | #1
On 4/25/21 12:07 AM, Muchun Song wrote:
> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> index d523a345dc86..d3abaaec2a22 100644
> --- a/include/linux/hugetlb.h
> +++ b/include/linux/hugetlb.h
> @@ -525,6 +525,7 @@ unsigned long hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
>   *	code knows it has only reference.  All other examinations and
>   *	modifications require hugetlb_lock.
>   * HPG_freed - Set when page is on the free lists.
> + * HPG_vmemmap_optimized - Set when the vmemmap pages of the page are freed.
>   *	Synchronization: hugetlb_lock held for examination and modification.
>   */
>  enum hugetlb_page_flags {
> @@ -532,6 +533,7 @@ enum hugetlb_page_flags {
>  	HPG_migratable,
>  	HPG_temporary,
>  	HPG_freed,
> +	HPG_vmemmap_optimized,
>  	__NR_HPAGEFLAGS,
>  };
>  
> @@ -577,6 +579,7 @@ HPAGEFLAG(RestoreReserve, restore_reserve)
>  HPAGEFLAG(Migratable, migratable)
>  HPAGEFLAG(Temporary, temporary)
>  HPAGEFLAG(Freed, freed)
> +HPAGEFLAG(VmemmapOptimized, vmemmap_optimized)
>  
>  #ifdef CONFIG_HUGETLB_PAGE
>  

During migration, the page->private field of the original page may be
cleared.  This will clear all hugetlb specific flags.  Prior to this
new flag that was OK, as the only flag which could be set during migration
was the Temporary flag and that is transfered to the target page.

If VmemmapOptimized optimized flag is cleared in the original page, we
will get an addressing exception as shown below.

We should preserve page->private with something like this:

diff --git a/mm/migrate.c b/mm/migrate.c
index b234c3f3acb7..128e3e4126a2 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -625,7 +625,9 @@ void migrate_page_states(struct page *newpage, struct page *page)
 	if (PageSwapCache(page))
 		ClearPageSwapCache(page);
 	ClearPagePrivate(page);
-	set_page_private(page, 0);
+	/* page->private contains hugetlb specific flags */
+	if (!PageHuge(page))
+		set_page_private(page, 0);
 
 	/*
 	 * If any waiters have accumulated on the new page then
Muchun Song April 29, 2021, 4:05 a.m. UTC | #2
On Thu, Apr 29, 2021 at 10:43 AM Mike Kravetz <mike.kravetz@oracle.com> wrote:
>
> On 4/25/21 12:07 AM, Muchun Song wrote:
> > diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> > index d523a345dc86..d3abaaec2a22 100644
> > --- a/include/linux/hugetlb.h
> > +++ b/include/linux/hugetlb.h
> > @@ -525,6 +525,7 @@ unsigned long hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
> >   *   code knows it has only reference.  All other examinations and
> >   *   modifications require hugetlb_lock.
> >   * HPG_freed - Set when page is on the free lists.
> > + * HPG_vmemmap_optimized - Set when the vmemmap pages of the page are freed.
> >   *   Synchronization: hugetlb_lock held for examination and modification.
> >   */
> >  enum hugetlb_page_flags {
> > @@ -532,6 +533,7 @@ enum hugetlb_page_flags {
> >       HPG_migratable,
> >       HPG_temporary,
> >       HPG_freed,
> > +     HPG_vmemmap_optimized,
> >       __NR_HPAGEFLAGS,
> >  };
> >
> > @@ -577,6 +579,7 @@ HPAGEFLAG(RestoreReserve, restore_reserve)
> >  HPAGEFLAG(Migratable, migratable)
> >  HPAGEFLAG(Temporary, temporary)
> >  HPAGEFLAG(Freed, freed)
> > +HPAGEFLAG(VmemmapOptimized, vmemmap_optimized)
> >
> >  #ifdef CONFIG_HUGETLB_PAGE
> >
>
> During migration, the page->private field of the original page may be
> cleared.  This will clear all hugetlb specific flags.  Prior to this
> new flag that was OK, as the only flag which could be set during migration
> was the Temporary flag and that is transfered to the target page.

I didn't realize this when I introduce the VmemmapOptimized.
Anyway, thanks for you pointed out this. I will fix this.

>
> If VmemmapOptimized optimized flag is cleared in the original page, we
> will get an addressing exception as shown below.

Thanks for your test.

>
> We should preserve page->private with something like this:
>
> diff --git a/mm/migrate.c b/mm/migrate.c
> index b234c3f3acb7..128e3e4126a2 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -625,7 +625,9 @@ void migrate_page_states(struct page *newpage, struct page *page)
>         if (PageSwapCache(page))
>                 ClearPageSwapCache(page);
>         ClearPagePrivate(page);
> -       set_page_private(page, 0);
> +       /* page->private contains hugetlb specific flags */
> +       if (!PageHuge(page))
> +               set_page_private(page, 0);
>
>         /*
>          * If any waiters have accumulated on the new page then
>
> --
> Mike Kravetz
>
>
> [  209.568110] BUG: unable to handle page fault for address: ffffea0004a5a000
> [  209.569417] #PF: supervisor write access in kernel mode
> [  209.570932] #PF: error_code(0x0003) - permissions violation
> [  209.572059] PGD 23fff8067 P4D 23fff8067 PUD 23fff7067 PMD 23ffd9067 PTE 800000021c98e061
> [  209.573679] Oops: 0003 [#1] SMP PTI
> [  209.574410] CPU: 1 PID: 1011 Comm: bash Not tainted 5.12.0-rc8-mm1+ #3
> [  209.575730] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-1.fc33 04/01/2014
> [  209.577530] RIP: 0010:__update_and_free_page+0x58/0x2c0
> [  209.578618] Code: a3 01 00 00 49 b8 00 00 00 00 00 16 00 00 4c 89 e0 bf 01 00 00 00 49 b9 00 00 00 00 00 ea ff ff 4d 01 e0 49 c1 f8 06 83 c2 01 <48> 81 20 d4 5e ff ff 48 83 c0 40 f7 c2 ff 03 00 00 0f 84 f3 00 00
> [  209.582603] RSP: 0018:ffffc90001fdfa60 EFLAGS: 00010206
> [  209.583629] RAX: ffffea0004a5a000 RBX: 0000000000000000 RCX: 0000000000000009
> [  209.585148] RDX: 0000000000000081 RSI: 0000000000000200 RDI: 0000000000000001
> [  209.586649] RBP: ffffffff839ada30 R08: 0000000000129600 R09: ffffea0000000000
> [  209.588096] R10: 0000000000000001 R11: 0000000000000001 R12: ffffea0004a58000
> [  209.589643] R13: 0000000000000200 R14: ffffea0005ff8000 R15: ffffc90001fdfba0
> [  209.591194] FS:  00007f1e50065740(0000) GS:ffff888237d00000(0000) knlGS:0000000000000000
> [  209.592989] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [  209.594222] CR2: ffffea0004a5a000 CR3: 000000018cd46004 CR4: 0000000000370ee0
> [  209.595762] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> [  209.597302] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> [  209.598925] Call Trace:
> [  209.599496]  migrate_pages+0xd8f/0x1030
> [  209.600372]  ? trace_event_raw_event_mm_migrate_pages_start+0xa0/0xa0
> [  209.601745]  ? alloc_migration_target+0x1c0/0x1c0
> [  209.602787]  alloc_contig_range+0x1e3/0x3d0
> [  209.603718]  cma_alloc+0x1ae/0x5f0
> [  209.604486]  alloc_fresh_huge_page+0x67/0x190
> [  209.605481]  alloc_pool_huge_page+0x72/0xf0
> [  209.606423]  set_max_huge_pages+0x128/0x2c0
> [  209.607369]  __nr_hugepages_store_common+0x3d/0xb0
> [  209.608442]  ? _kstrtoull+0x35/0xd0
> [  209.609225]  nr_hugepages_store+0x73/0x80
> [  209.610140]  kernfs_fop_write_iter+0x127/0x1c0
> [  209.611162]  new_sync_write+0x11f/0x1b0
> [  209.612069]  vfs_write+0x26f/0x380
> [  209.612880]  ksys_write+0x68/0xe0
> [  209.613628]  do_syscall_64+0x40/0x80
> [  209.614456]  entry_SYSCALL_64_after_hwframe+0x44/0xae
> [  209.615589] RIP: 0033:0x7f1e50155ff8
> [  209.616474] Code: 89 02 48 c7 c0 ff ff ff ff eb b3 0f 1f 80 00 00 00 00 f3 0f 1e fa 48 8d 05 25 77 0d 00 8b 00 85 c0 75 17 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 58 c3 0f 1f 80 00 00 00 00 41 54 49 89 d4 55
> [  209.620629] RSP: 002b:00007ffd7e3f97c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
> [  209.622319] RAX: ffffffffffffffda RBX: 0000000000000002 RCX: 00007f1e50155ff8
> [  209.623966] RDX: 0000000000000002 RSI: 00005585ef557960 RDI: 0000000000000001
> [  209.625568] RBP: 00005585ef557960 R08: 000000000000000a R09: 00007f1e501e7e80
> [  209.627262] R10: 000000000000000a R11: 0000000000000246 R12: 00007f1e50229780
> [  209.628916] R13: 0000000000000002 R14: 00007f1e50224740 R15: 0000000000000002
> [  209.630457] Modules linked in: ip6t_rpfilter ip6t_REJECT nf_reject_ipv6 xt_conntrack ebtable_nat ip6table_nat ip6table_mangle ip6table_raw ip6table_security iptable_nat nf_nat iptable_mangle iptable_raw iptable_security nf_conntrack rfkill nf_defrag_ipv6 nf_defrag_ipv4 ebtable_filter ebtables 9p ip6table_filter ip6_tables sunrpc snd_hda_codec_generic crct10dif_pclmul crc32_pclmul snd_hda_intel snd_intel_dspcfg ghash_clmulni_intel snd_hda_codec snd_hwdep joydev snd_hda_core snd_seq snd_seq_device snd_pcm virtio_balloon snd_timer snd soundcore 9pnet_virtio i2c_piix4 9pnet virtio_blk virtio_console virtio_net net_failover failover 8139too qxl drm_ttm_helper ttm drm_kms_helper crc32c_intel serio_raw drm 8139cp mii ata_generic virtio_pci virtio_pci_modern_dev virtio_ring pata_acpi virtio
> [  209.647105] CR2: ffffea0004a5a000
> [  209.647913] ---[ end trace 48e9b007521233a7 ]---
diff mbox series

Patch

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/Documentation/admin-guide/mm/memory-hotplug.rst b/Documentation/admin-guide/mm/memory-hotplug.rst
index 05d51d2d8beb..c6bae2d77160 100644
--- a/Documentation/admin-guide/mm/memory-hotplug.rst
+++ b/Documentation/admin-guide/mm/memory-hotplug.rst
@@ -357,6 +357,19 @@  creates ZONE_MOVABLE as following.
    Unfortunately, there is no information to show which memory block belongs
    to ZONE_MOVABLE. This is TBD.
 
+   Memory offlining can fail when dissolving a free huge page on ZONE_MOVABLE
+   and the feature of freeing unused vmemmap pages associated with each hugetlb
+   page is enabled.
+
+   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.
+
 .. note::
    Techniques that rely on long-term pinnings of memory (especially, RDMA and
    vfio) are fundamentally problematic with ZONE_MOVABLE and, therefore, memory
diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index d523a345dc86..d3abaaec2a22 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -525,6 +525,7 @@  unsigned long hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
  *	code knows it has only reference.  All other examinations and
  *	modifications require hugetlb_lock.
  * HPG_freed - Set when page is on the free lists.
+ * HPG_vmemmap_optimized - Set when the vmemmap pages of the page are freed.
  *	Synchronization: hugetlb_lock held for examination and modification.
  */
 enum hugetlb_page_flags {
@@ -532,6 +533,7 @@  enum hugetlb_page_flags {
 	HPG_migratable,
 	HPG_temporary,
 	HPG_freed,
+	HPG_vmemmap_optimized,
 	__NR_HPAGEFLAGS,
 };
 
@@ -577,6 +579,7 @@  HPAGEFLAG(RestoreReserve, restore_reserve)
 HPAGEFLAG(Migratable, migratable)
 HPAGEFLAG(Temporary, temporary)
 HPAGEFLAG(Freed, freed)
+HPAGEFLAG(VmemmapOptimized, vmemmap_optimized)
 
 #ifdef CONFIG_HUGETLB_PAGE
 
diff --git a/include/linux/mm.h b/include/linux/mm.h
index a4d160ddb749..d0854828bb9c 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -3048,6 +3048,8 @@  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 72ce4d28441a..1e3e3a8e05e2 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1376,6 +1376,39 @@  static void remove_hugetlb_page(struct hstate *h, struct page *page,
 	h->nr_huge_pages_node[nid]--;
 }
 
+static void add_hugetlb_page(struct hstate *h, struct page *page,
+			     bool adjust_surplus)
+{
+	int zeroed;
+	int nid = page_to_nid(page);
+
+	VM_BUG_ON_PAGE(!HPageVmemmapOptimized(page), page);
+
+	lockdep_assert_held(&hugetlb_lock);
+
+	INIT_LIST_HEAD(&page->lru);
+	h->nr_huge_pages++;
+	h->nr_huge_pages_node[nid]++;
+
+	if (adjust_surplus) {
+		h->surplus_huge_pages++;
+		h->surplus_huge_pages_node[nid]++;
+	}
+
+	set_compound_page_dtor(page, HUGETLB_PAGE_DTOR);
+	set_page_private(page, 0);
+	SetHPageVmemmapOptimized(page);
+
+	/*
+	 * This page is now managed by the hugetlb allocator and has
+	 * no users -- drop the last reference.
+	 */
+	zeroed = put_page_testzero(page);
+	VM_BUG_ON_PAGE(!zeroed, page);
+	arch_clear_hugepage_flags(page);
+	enqueue_huge_page(h, page);
+}
+
 static void __update_and_free_page(struct hstate *h, struct page *page)
 {
 	int i;
@@ -1384,6 +1417,18 @@  static void __update_and_free_page(struct hstate *h, struct page *page)
 	if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported())
 		return;
 
+	if (alloc_huge_page_vmemmap(h, page)) {
+		spin_lock_irq(&hugetlb_lock);
+		/*
+		 * 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.
+		 */
+		add_hugetlb_page(h, page, true);
+		spin_unlock_irq(&hugetlb_lock);
+		return;
+	}
+
 	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 |
@@ -1450,7 +1495,7 @@  static inline void flush_free_hpage_work(struct hstate *h)
 static void update_and_free_page(struct hstate *h, struct page *page,
 				 bool atomic)
 {
-	if (!free_vmemmap_pages_per_hpage(h) || !atomic) {
+	if (!HPageVmemmapOptimized(page) || !atomic) {
 		__update_and_free_page(h, page);
 		return;
 	}
@@ -1809,10 +1854,14 @@  static struct page *remove_pool_huge_page(struct hstate *h,
  * 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)
 {
@@ -1854,19 +1903,38 @@  int dissolve_free_huge_page(struct page *page)
 			goto retry;
 		}
 
-		/*
-		 * Move PageHWPoison flag from head page to the raw error page,
-		 * which makes any subpages rather than the error page reusable.
-		 */
-		if (PageHWPoison(head) && page != head) {
-			SetPageHWPoison(page);
-			ClearPageHWPoison(head);
-		}
 		remove_hugetlb_page(h, page, false);
 		h->max_huge_pages--;
 		spin_unlock_irq(&hugetlb_lock);
-		update_and_free_page(h, head, false);
-		return 0;
+
+		/*
+		 * Normally update_and_free_page will allocate required vmemmmap
+		 * before freeing the page.  update_and_free_page will fail to
+		 * free the page if it can not allocate required vmemmap.  We
+		 * need to adjust max_huge_pages if the page is not freed.
+		 * Attempt to allocate vmemmmap here so that we can take
+		 * appropriate action on failure.
+		 */
+		rc = alloc_huge_page_vmemmap(h, page);
+		if (!rc) {
+			/*
+			 * Move PageHWPoison flag from head page to the raw
+			 * error page, which makes any subpages rather than
+			 * the error page reusable.
+			 */
+			if (PageHWPoison(head) && page != head) {
+				SetPageHWPoison(page);
+				ClearPageHWPoison(head);
+			}
+			update_and_free_page(h, head, false);
+		} else {
+			spin_lock_irq(&hugetlb_lock);
+			add_hugetlb_page(h, page, false);
+			h->max_huge_pages++;
+			spin_unlock_irq(&hugetlb_lock);
+		}
+
+		return rc;
 	}
 out:
 	spin_unlock_irq(&hugetlb_lock);
diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
index cb28c5b6c9ff..a897c7778246 100644
--- a/mm/hugetlb_vmemmap.c
+++ b/mm/hugetlb_vmemmap.c
@@ -185,6 +185,38 @@  static inline unsigned long free_vmemmap_pages_size_per_hpage(struct hstate *h)
 	return (unsigned long)free_vmemmap_pages_per_hpage(h) << PAGE_SHIFT;
 }
 
+/*
+ * Previously discarded vmemmap pages will be allocated and remapping
+ * after this function returns zero.
+ */
+int alloc_huge_page_vmemmap(struct hstate *h, struct page *head)
+{
+	int ret;
+	unsigned long vmemmap_addr = (unsigned long)head;
+	unsigned long vmemmap_end, vmemmap_reuse;
+
+	if (!HPageVmemmapOptimized(head))
+		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.
+	 */
+	ret = vmemmap_remap_alloc(vmemmap_addr, vmemmap_end, vmemmap_reuse,
+				  GFP_KERNEL | __GFP_NORETRY | __GFP_THISNODE);
+
+	if (!ret)
+		ClearHPageVmemmapOptimized(head);
+
+	return ret;
+}
+
 void free_huge_page_vmemmap(struct hstate *h, struct page *head)
 {
 	unsigned long vmemmap_addr = (unsigned long)head;
@@ -203,4 +235,6 @@  void free_huge_page_vmemmap(struct hstate *h, struct page *head)
 	 * which the range [@vmemmap_addr, @vmemmap_end] is mapped to.
 	 */
 	vmemmap_remap_free(vmemmap_addr, vmemmap_end, vmemmap_reuse);
+
+	SetHPageVmemmapOptimized(head);
 }
diff --git a/mm/hugetlb_vmemmap.h b/mm/hugetlb_vmemmap.h
index 01f8637adbe0..a37771b0b82a 100644
--- a/mm/hugetlb_vmemmap.h
+++ b/mm/hugetlb_vmemmap.h
@@ -11,6 +11,7 @@ 
 #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);
 
 /*
@@ -25,6 +26,11 @@  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)
 {
 }
diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
index 7d40b5bd7046..693de0aec7a8 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,
@@ -224,6 +225,78 @@  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.