* [PATCH 6.18.y 2/5] mm/hugetlb: defer vmemmap population for bootmem hugepages
2026-09-03 16:59 ` [PATCH 6.18.y 1/5] mm: rework compound_head() for power-of-2 sizeof(struct page) Sasha Levin
@ 2026-09-03 16:59 ` Sasha Levin
2026-09-03 16:59 ` [PATCH 6.18.y 3/5] mm/hugetlb: refactor code around vmemmap_walk Sasha Levin
` (2 subsequent siblings)
3 siblings, 0 replies; 6+ messages in thread
From: Sasha Levin @ 2026-09-03 16:59 UTC (permalink / raw)
To: stable
Cc: Kiryl Shutsemau (Meta), David Hildenbrand (Arm), Albert Ou,
Alexandre Ghiti, Baoquan He, Christoph Lameter, David Rientjes,
Frank van der Linden, Harry Yoo, Huacai Chen, Johannes Weiner,
Jonathan Corbet, Lorenzo Stoakes, Matthew Wilcox (Oracle),
Michal Hocko, Mike Rapoport, Muchun Song, Oscar Salvador,
Palmer Dabbelt, Paul Walmsley, Roman Gushchin, Usama Arif,
Vlastimil Babka, WANG Xuerui, Zi Yan, Andrew Morton, Sasha Levin
From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>
[ Upstream commit 209e6d9eb13aaf1b6e0fc6f76afc00d055e5ba12 ]
Currently, the vmemmap for bootmem-allocated gigantic pages is populated
early in hugetlb_vmemmap_init_early(). However, the zone information is
only available after zones are initialized. If it is later discovered
that a page spans multiple zones, the HVO mapping must be undone and
replaced with a normal mapping using vmemmap_undo_hvo().
Defer the actual vmemmap population to hugetlb_vmemmap_init_late(). At
this stage, zones are already initialized, so it can be checked if the
page is valid for HVO before deciding how to populate the vmemmap.
This allows us to remove vmemmap_undo_hvo() and the complex logic required
to rollback HVO mappings.
In hugetlb_vmemmap_init_late(), if HVO population fails or if the zones
are invalid, fall back to a normal vmemmap population.
Postponing population until hugetlb_vmemmap_init_late() also makes zone
information available from within vmemmap_populate_hvo().
Link: https://lkml.kernel.org/r/20260227194302.274384-10-kas@kernel.org
Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Alexandre Ghiti <alex@ghiti.fr>
Cc: Baoquan He <bhe@redhat.com>
Cc: Christoph Lameter <cl@gentwo.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Frank van der Linden <fvdl@google.com>
Cc: Harry Yoo <harry.yoo@oracle.com>
Cc: Huacai Chen <chenhuacai@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Usama Arif <usamaarif642@gmail.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: WANG Xuerui <kernel@xen0n.name>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Stable-dep-of: 6e25c6a9c7ef ("mm/hugetlb_vmemmap: fix __hugetlb_vmemmap_optimize_folios()")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
include/linux/mm.h | 2 --
mm/hugetlb_vmemmap.c | 37 +++++++++++++++----------------
mm/sparse-vmemmap.c | 53 --------------------------------------------
3 files changed, 18 insertions(+), 74 deletions(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 92ba2489f2374..50710a5d4a05f 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -4101,8 +4101,6 @@ int vmemmap_populate(unsigned long start, unsigned long end, int node,
struct vmem_altmap *altmap);
int vmemmap_populate_hvo(unsigned long start, unsigned long end, int node,
unsigned long headsize);
-int vmemmap_undo_hvo(unsigned long start, unsigned long end, int node,
- unsigned long headsize);
void vmemmap_wrprotect_hvo(unsigned long start, unsigned long end, int node,
unsigned long headsize);
void vmemmap_populate_print_last(void);
diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
index dd3f8438a9b64..b30a630dae62a 100644
--- a/mm/hugetlb_vmemmap.c
+++ b/mm/hugetlb_vmemmap.c
@@ -790,7 +790,6 @@ void __init hugetlb_vmemmap_init_early(int nid)
{
unsigned long psize, paddr, section_size;
unsigned long ns, i, pnum, pfn, nr_pages;
- unsigned long start, end;
struct huge_bootmem_page *m = NULL;
void *map;
@@ -816,14 +815,6 @@ void __init hugetlb_vmemmap_init_early(int nid)
paddr = virt_to_phys(m);
pfn = PHYS_PFN(paddr);
map = pfn_to_page(pfn);
- start = (unsigned long)map;
- end = start + nr_pages * sizeof(struct page);
-
- if (vmemmap_populate_hvo(start, end, nid,
- HUGETLB_VMEMMAP_RESERVE_SIZE) < 0)
- continue;
-
- memmap_boot_pages_add(HUGETLB_VMEMMAP_RESERVE_SIZE / PAGE_SIZE);
pnum = pfn_to_section_nr(pfn);
ns = psize / section_size;
@@ -861,28 +852,36 @@ void __init hugetlb_vmemmap_init_late(int nid)
h = m->hstate;
pfn = PHYS_PFN(phys);
nr_pages = pages_per_huge_page(h);
+ map = pfn_to_page(pfn);
+ start = (unsigned long)map;
+ end = start + nr_pages * sizeof(struct page);
if (!hugetlb_bootmem_page_zones_valid(nid, m)) {
/*
* Oops, the hugetlb page spans multiple zones.
- * Remove it from the list, and undo HVO.
+ * Remove it from the list, and populate it normally.
*/
list_del(&m->list);
- map = pfn_to_page(pfn);
-
- start = (unsigned long)map;
- end = start + nr_pages * sizeof(struct page);
-
- vmemmap_undo_hvo(start, end, nid,
- HUGETLB_VMEMMAP_RESERVE_SIZE);
- nr_mmap = end - start - HUGETLB_VMEMMAP_RESERVE_SIZE;
+ vmemmap_populate(start, end, nid, NULL);
+ nr_mmap = end - start;
memmap_boot_pages_add(DIV_ROUND_UP(nr_mmap, PAGE_SIZE));
memblock_phys_free(phys, huge_page_size(h));
continue;
- } else
+ }
+
+ if (vmemmap_populate_hvo(start, end, nid,
+ HUGETLB_VMEMMAP_RESERVE_SIZE) < 0) {
+ /* Fallback if HVO population fails */
+ vmemmap_populate(start, end, nid, NULL);
+ nr_mmap = end - start;
+ } else {
m->flags |= HUGE_BOOTMEM_ZONES_VALID;
+ nr_mmap = HUGETLB_VMEMMAP_RESERVE_SIZE;
+ }
+
+ memmap_boot_pages_add(DIV_ROUND_UP(nr_mmap, PAGE_SIZE));
}
}
#endif
diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
index 37522d6cb3988..032a81450838b 100644
--- a/mm/sparse-vmemmap.c
+++ b/mm/sparse-vmemmap.c
@@ -302,59 +302,6 @@ int __meminit vmemmap_populate_basepages(unsigned long start, unsigned long end,
return vmemmap_populate_range(start, end, node, altmap, -1, 0);
}
-/*
- * Undo populate_hvo, and replace it with a normal base page mapping.
- * Used in memory init in case a HVO mapping needs to be undone.
- *
- * This can happen when it is discovered that a memblock allocated
- * hugetlb page spans multiple zones, which can only be verified
- * after zones have been initialized.
- *
- * We know that:
- * 1) The first @headsize / PAGE_SIZE vmemmap pages were individually
- * allocated through memblock, and mapped.
- *
- * 2) The rest of the vmemmap pages are mirrors of the last head page.
- */
-int __meminit vmemmap_undo_hvo(unsigned long addr, unsigned long end,
- int node, unsigned long headsize)
-{
- unsigned long maddr, pfn;
- pte_t *pte;
- int headpages;
-
- /*
- * Should only be called early in boot, so nothing will
- * be accessing these page structures.
- */
- WARN_ON(!early_boot_irqs_disabled);
-
- headpages = headsize >> PAGE_SHIFT;
-
- /*
- * Clear mirrored mappings for tail page structs.
- */
- for (maddr = addr + headsize; maddr < end; maddr += PAGE_SIZE) {
- pte = virt_to_kpte(maddr);
- pte_clear(&init_mm, maddr, pte);
- }
-
- /*
- * Clear and free mappings for head page and first tail page
- * structs.
- */
- for (maddr = addr; headpages-- > 0; maddr += PAGE_SIZE) {
- pte = virt_to_kpte(maddr);
- pfn = pte_pfn(ptep_get(pte));
- pte_clear(&init_mm, maddr, pte);
- memblock_phys_free(PFN_PHYS(pfn), PAGE_SIZE);
- }
-
- flush_tlb_kernel_range(addr, end);
-
- return vmemmap_populate(addr, end, node, NULL);
-}
-
/*
* Write protect the mirrored tail page structs for HVO. This will be
* called from the hugetlb code when gathering and initializing the
--
2.53.0
^ permalink raw reply related [flat|nested] 6+ messages in thread* [PATCH 6.18.y 3/5] mm/hugetlb: refactor code around vmemmap_walk
2026-09-03 16:59 ` [PATCH 6.18.y 1/5] mm: rework compound_head() for power-of-2 sizeof(struct page) Sasha Levin
2026-09-03 16:59 ` [PATCH 6.18.y 2/5] mm/hugetlb: defer vmemmap population for bootmem hugepages Sasha Levin
@ 2026-09-03 16:59 ` Sasha Levin
2026-09-03 16:59 ` [PATCH 6.18.y 4/5] hugetlb: remove VMEMMAP_SYNCHRONIZE_RCU Sasha Levin
2026-09-03 16:59 ` [PATCH 6.18.y 5/5] mm/hugetlb_vmemmap: fix __hugetlb_vmemmap_optimize_folios() Sasha Levin
3 siblings, 0 replies; 6+ messages in thread
From: Sasha Levin @ 2026-09-03 16:59 UTC (permalink / raw)
To: stable
Cc: Kiryl Shutsemau, Muchun Song, Albert Ou, Alexandre Ghiti,
Baoquan He, Christoph Lameter, David Hildenbrand (arm),
David Rientjes, Frank van der Linden, Harry Yoo, Huacai Chen,
Johannes Weiner, Jonathan Corbet, Lorenzo Stoakes,
Matthew Wilcox (Oracle), Michal Hocko, Mike Rapoport,
Oscar Salvador, Palmer Dabbelt, Paul Walmsley, Roman Gushchin,
Usama Arif, Vlastimil Babka, WANG Xuerui, Zi Yan, Andrew Morton,
Sasha Levin
From: Kiryl Shutsemau <kas@kernel.org>
[ Upstream commit c0b495b91a47b6c5ee54cf00e620dbadeb884253 ]
To prepare for removing fake head pages, the vmemmap_walk code is being
reworked.
The reuse_page and reuse_addr variables are being eliminated. There will
no longer be an expectation regarding the reuse address in relation to the
operated range. Instead, the caller will provide head and tail vmemmap
pages.
Currently, vmemmap_head and vmemmap_tail are set to the same page, but
this will change in the future.
The only functional change is that __hugetlb_vmemmap_optimize_folio() will
abandon optimization if memory allocation fails.
Link: https://lkml.kernel.org/r/20260227194302.274384-11-kas@kernel.org
Signed-off-by: Kiryl Shutsemau <kas@kernel.org>
Reviewed-by: Muchun Song <muchun.song@linux.dev>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Alexandre Ghiti <alex@ghiti.fr>
Cc: Baoquan He <bhe@redhat.com>
Cc: Christoph Lameter <cl@gentwo.org>
Cc: David Hildenbrand (arm) <david@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Frank van der Linden <fvdl@google.com>
Cc: Harry Yoo <harry.yoo@oracle.com>
Cc: Huacai Chen <chenhuacai@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Usama Arif <usamaarif642@gmail.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: WANG Xuerui <kernel@xen0n.name>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Stable-dep-of: 6e25c6a9c7ef ("mm/hugetlb_vmemmap: fix __hugetlb_vmemmap_optimize_folios()")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
mm/hugetlb_vmemmap.c | 224 +++++++++++++++++--------------------------
1 file changed, 89 insertions(+), 135 deletions(-)
diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
index b30a630dae62a..1f1c2ccca3159 100644
--- a/mm/hugetlb_vmemmap.c
+++ b/mm/hugetlb_vmemmap.c
@@ -24,8 +24,8 @@
*
* @remap_pte: called for each lowest-level entry (PTE).
* @nr_walked: the number of walked pte.
- * @reuse_page: the page which is reused for the tail vmemmap pages.
- * @reuse_addr: the virtual address of the @reuse_page page.
+ * @vmemmap_head: the page to be installed as first in the vmemmap range
+ * @vmemmap_tail: the page to be installed as non-first in the vmemmap range
* @vmemmap_pages: the list head of the vmemmap pages that can be freed
* or is mapped from.
* @flags: used to modify behavior in vmemmap page table walking
@@ -34,11 +34,13 @@
struct vmemmap_remap_walk {
void (*remap_pte)(pte_t *pte, unsigned long addr,
struct vmemmap_remap_walk *walk);
+
unsigned long nr_walked;
- struct page *reuse_page;
- unsigned long reuse_addr;
+ struct page *vmemmap_head;
+ struct page *vmemmap_tail;
struct list_head *vmemmap_pages;
+
/* Skip the TLB flush when we split the PMD */
#define VMEMMAP_SPLIT_NO_TLB_FLUSH BIT(0)
/* Skip the TLB flush when we remap the PTE */
@@ -140,14 +142,7 @@ static int vmemmap_pte_entry(pte_t *pte, unsigned long addr,
{
struct vmemmap_remap_walk *vmemmap_walk = walk->private;
- /*
- * The reuse_page is found 'first' in page table walking before
- * starting remapping.
- */
- if (!vmemmap_walk->reuse_page)
- vmemmap_walk->reuse_page = pte_page(ptep_get(pte));
- else
- vmemmap_walk->remap_pte(pte, addr, vmemmap_walk);
+ vmemmap_walk->remap_pte(pte, addr, vmemmap_walk);
vmemmap_walk->nr_walked++;
return 0;
@@ -207,18 +202,12 @@ static void free_vmemmap_page_list(struct list_head *list)
static void vmemmap_remap_pte(pte_t *pte, unsigned long addr,
struct vmemmap_remap_walk *walk)
{
- /*
- * Remap the tail pages as read-only to catch illegal write operation
- * to the tail pages.
- */
- pgprot_t pgprot = PAGE_KERNEL_RO;
struct page *page = pte_page(ptep_get(pte));
pte_t entry;
/* Remapping the head page requires r/w */
- if (unlikely(addr == walk->reuse_addr)) {
- pgprot = PAGE_KERNEL;
- list_del(&walk->reuse_page->lru);
+ if (unlikely(walk->nr_walked == 0 && walk->vmemmap_head)) {
+ list_del(&walk->vmemmap_head->lru);
/*
* Makes sure that preceding stores to the page contents from
@@ -226,53 +215,50 @@ static void vmemmap_remap_pte(pte_t *pte, unsigned long addr,
* write.
*/
smp_wmb();
+
+ entry = mk_pte(walk->vmemmap_head, PAGE_KERNEL);
+ } else {
+ /*
+ * Remap the tail pages as read-only to catch illegal write
+ * operation to the tail pages.
+ */
+ entry = mk_pte(walk->vmemmap_tail, PAGE_KERNEL_RO);
}
- entry = mk_pte(walk->reuse_page, pgprot);
list_add(&page->lru, walk->vmemmap_pages);
set_pte_at(&init_mm, addr, pte, entry);
}
-/*
- * How many struct page structs need to be reset. When we reuse the head
- * struct page, the special metadata (e.g. page->flags or page->mapping)
- * cannot copy to the tail struct page structs. The invalid value will be
- * checked in the free_tail_page_prepare(). In order to avoid the message
- * of "corrupted mapping in tail page". We need to reset at least 4 (one
- * head struct page struct and three tail struct page structs) struct page
- * structs.
- */
-#define NR_RESET_STRUCT_PAGE 4
-
-static inline void reset_struct_pages(struct page *start)
-{
- struct page *from = start + NR_RESET_STRUCT_PAGE;
-
- BUILD_BUG_ON(NR_RESET_STRUCT_PAGE * 2 > PAGE_SIZE / sizeof(struct page));
- memcpy(start, from, sizeof(*from) * NR_RESET_STRUCT_PAGE);
-}
-
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(ptep_get(pte)) != walk->reuse_page);
+ struct page *from, *to;
page = list_first_entry(walk->vmemmap_pages, struct page, lru);
list_del(&page->lru);
+
+ /*
+ * Initialize tail pages in the newly allocated vmemmap page.
+ *
+ * There is folio-scope metadata that is encoded in the first few
+ * tail pages.
+ *
+ * Use the value last tail page in the page with the head page
+ * to initialize the rest of tail pages.
+ */
+ from = compound_head((struct page *)addr) +
+ PAGE_SIZE / sizeof(struct page) - 1;
to = page_to_virt(page);
- copy_page(to, (void *)walk->reuse_addr);
- reset_struct_pages(to);
+ for (int i = 0; i < PAGE_SIZE / sizeof(struct page); i++, to++)
+ *to = *from;
/*
* Makes sure that preceding stores to the page contents become visible
* before the set_pte_at() write.
*/
smp_wmb();
- set_pte_at(&init_mm, addr, pte, mk_pte(page, pgprot));
+ set_pte_at(&init_mm, addr, pte, mk_pte(page, PAGE_KERNEL));
}
/**
@@ -282,33 +268,28 @@ static void vmemmap_restore_pte(pte_t *pte, unsigned long addr,
* to remap.
* @end: end address of the vmemmap virtual address range that we want to
* remap.
- * @reuse: reuse address.
- *
* Return: %0 on success, negative error code otherwise.
*/
-static int vmemmap_remap_split(unsigned long start, unsigned long end,
- unsigned long reuse)
+static int vmemmap_remap_split(unsigned long start, unsigned long end)
{
struct vmemmap_remap_walk walk = {
.remap_pte = NULL,
.flags = VMEMMAP_SPLIT_NO_TLB_FLUSH,
};
- /* See the comment in the vmemmap_remap_free(). */
- BUG_ON(start - reuse != PAGE_SIZE);
-
- return vmemmap_remap_range(reuse, end, &walk);
+ return vmemmap_remap_range(start, end, &walk);
}
/**
* vmemmap_remap_free - remap the vmemmap virtual address range [@start, @end)
- * to the page which @reuse is mapped to, then free vmemmap
- * which the range are mapped to.
+ * to use @vmemmap_head/tail, then free vmemmap which
+ * the range are mapped to.
* @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.
+ * @vmemmap_head: the page to be installed as first in the vmemmap range
+ * @vmemmap_tail: the page to be installed as non-first in the vmemmap range
* @vmemmap_pages: list to deposit vmemmap pages to be freed. It is callers
* responsibility to free pages.
* @flags: modifications to vmemmap_remap_walk flags
@@ -316,69 +297,38 @@ static int vmemmap_remap_split(unsigned long start, unsigned long end,
* Return: %0 on success, negative error code otherwise.
*/
static int vmemmap_remap_free(unsigned long start, unsigned long end,
- unsigned long reuse,
+ struct page *vmemmap_head,
+ struct page *vmemmap_tail,
struct list_head *vmemmap_pages,
unsigned long flags)
{
int ret;
struct vmemmap_remap_walk walk = {
.remap_pte = vmemmap_remap_pte,
- .reuse_addr = reuse,
+ .vmemmap_head = vmemmap_head,
+ .vmemmap_tail = vmemmap_tail,
.vmemmap_pages = vmemmap_pages,
.flags = flags,
};
- int nid = page_to_nid((struct page *)reuse);
- gfp_t gfp_mask = GFP_KERNEL | __GFP_NORETRY | __GFP_NOWARN;
- /*
- * Allocate a new head vmemmap page to avoid breaking a contiguous
- * block of struct page memory when freeing it back to page allocator
- * in free_vmemmap_page_list(). This will allow the likely contiguous
- * struct page backing memory to be kept contiguous and allowing for
- * more allocations of hugepages. Fallback to the currently
- * mapped head page in case should it fail to allocate.
- */
- walk.reuse_page = alloc_pages_node(nid, gfp_mask, 0);
- if (walk.reuse_page) {
- copy_page(page_to_virt(walk.reuse_page),
- (void *)walk.reuse_addr);
- list_add(&walk.reuse_page->lru, vmemmap_pages);
- memmap_pages_add(1);
- }
+ ret = vmemmap_remap_range(start, end, &walk);
+ if (!ret || !walk.nr_walked)
+ return ret;
+
+ end = start + walk.nr_walked * PAGE_SIZE;
/*
- * In order to make remapping routine most efficient for the huge pages,
- * the routine of vmemmap page table walking has the following rules
- * (see more details from the vmemmap_pte_range()):
- *
- * - The range [@start, @end) and the range [@reuse, @reuse + PAGE_SIZE)
- * should be continuous.
- * - The @reuse address is part of the range [@reuse, @end) that we are
- * walking which is passed to vmemmap_remap_range().
- * - The @reuse address is the first in the complete range.
- *
- * So we need to make sure that @start and @reuse meet the above rules.
+ * vmemmap_pages contains pages from the previous vmemmap_remap_range()
+ * call which failed. These are pages which were removed from
+ * the vmemmap. They will be restored in the following call.
*/
- BUG_ON(start - reuse != PAGE_SIZE);
+ walk = (struct vmemmap_remap_walk) {
+ .remap_pte = vmemmap_restore_pte,
+ .vmemmap_pages = vmemmap_pages,
+ .flags = 0,
+ };
- ret = vmemmap_remap_range(reuse, end, &walk);
- if (ret && walk.nr_walked) {
- end = reuse + walk.nr_walked * PAGE_SIZE;
- /*
- * vmemmap_pages contains pages from the previous
- * vmemmap_remap_range call which failed. These
- * are pages which were removed from the vmemmap.
- * They will be restored in the following call.
- */
- walk = (struct vmemmap_remap_walk) {
- .remap_pte = vmemmap_restore_pte,
- .reuse_addr = reuse,
- .vmemmap_pages = vmemmap_pages,
- .flags = 0,
- };
-
- vmemmap_remap_range(reuse, end, &walk);
- }
+ vmemmap_remap_range(start, end, &walk);
return ret;
}
@@ -415,29 +365,24 @@ static int alloc_vmemmap_page_list(unsigned long start, unsigned long end,
* to remap.
* @end: end address of the vmemmap virtual address range that we want to
* remap.
- * @reuse: reuse address.
* @flags: modifications to vmemmap_remap_walk flags
*
* Return: %0 on success, negative error code otherwise.
*/
static int vmemmap_remap_alloc(unsigned long start, unsigned long end,
- unsigned long reuse, unsigned long flags)
+ unsigned long flags)
{
LIST_HEAD(vmemmap_pages);
struct vmemmap_remap_walk walk = {
.remap_pte = vmemmap_restore_pte,
- .reuse_addr = reuse,
.vmemmap_pages = &vmemmap_pages,
.flags = flags,
};
- /* See the comment in the vmemmap_remap_free(). */
- BUG_ON(start - reuse != PAGE_SIZE);
-
if (alloc_vmemmap_page_list(start, end, &vmemmap_pages))
return -ENOMEM;
- return vmemmap_remap_range(reuse, end, &walk);
+ return vmemmap_remap_range(start, end, &walk);
}
DEFINE_STATIC_KEY_FALSE(hugetlb_optimize_vmemmap_key);
@@ -454,8 +399,7 @@ static int __hugetlb_vmemmap_restore_folio(const struct hstate *h,
struct folio *folio, unsigned long flags)
{
int ret;
- unsigned long vmemmap_start = (unsigned long)&folio->page, vmemmap_end;
- unsigned long vmemmap_reuse;
+ unsigned long vmemmap_start, vmemmap_end;
VM_WARN_ON_ONCE_FOLIO(!folio_test_hugetlb(folio), folio);
VM_WARN_ON_ONCE_FOLIO(folio_ref_count(folio), folio);
@@ -466,18 +410,18 @@ static int __hugetlb_vmemmap_restore_folio(const struct hstate *h,
if (flags & VMEMMAP_SYNCHRONIZE_RCU)
synchronize_rcu();
+ vmemmap_start = (unsigned long)&folio->page;
vmemmap_end = vmemmap_start + hugetlb_vmemmap_size(h);
- vmemmap_reuse = vmemmap_start;
+
vmemmap_start += HUGETLB_VMEMMAP_RESERVE_SIZE;
/*
* The pages which the vmemmap virtual address range [@vmemmap_start,
- * @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.
+ * @vmemmap_end) are mapped to are freed to the buddy allocator.
* When a HugeTLB page is freed to the buddy allocator, previously
* discarded vmemmap pages must be allocated and remapping.
*/
- ret = vmemmap_remap_alloc(vmemmap_start, vmemmap_end, vmemmap_reuse, flags);
+ ret = vmemmap_remap_alloc(vmemmap_start, vmemmap_end, flags);
if (!ret) {
folio_clear_hugetlb_vmemmap_optimized(folio);
static_branch_dec(&hugetlb_optimize_vmemmap_key);
@@ -565,9 +509,9 @@ static int __hugetlb_vmemmap_optimize_folio(const struct hstate *h,
struct list_head *vmemmap_pages,
unsigned long flags)
{
- int ret = 0;
- unsigned long vmemmap_start = (unsigned long)&folio->page, vmemmap_end;
- unsigned long vmemmap_reuse;
+ unsigned long vmemmap_start, vmemmap_end;
+ struct page *vmemmap_head, *vmemmap_tail;
+ int nid, ret = 0;
VM_WARN_ON_ONCE_FOLIO(!folio_test_hugetlb(folio), folio);
VM_WARN_ON_ONCE_FOLIO(folio_ref_count(folio), folio);
@@ -592,18 +536,30 @@ static int __hugetlb_vmemmap_optimize_folio(const struct hstate *h,
*/
folio_set_hugetlb_vmemmap_optimized(folio);
+ nid = folio_nid(folio);
+ vmemmap_head = alloc_pages_node(nid, GFP_KERNEL, 0);
+ if (!vmemmap_head) {
+ ret = -ENOMEM;
+ goto out;
+ }
+
+ copy_page(page_to_virt(vmemmap_head), folio);
+ list_add(&vmemmap_head->lru, vmemmap_pages);
+ memmap_pages_add(1);
+
+ vmemmap_tail = vmemmap_head;
+ vmemmap_start = (unsigned long)&folio->page;
vmemmap_end = vmemmap_start + hugetlb_vmemmap_size(h);
- vmemmap_reuse = vmemmap_start;
- vmemmap_start += HUGETLB_VMEMMAP_RESERVE_SIZE;
/*
- * Remap the vmemmap virtual address range [@vmemmap_start, @vmemmap_end)
- * to the page which @vmemmap_reuse is mapped to. Add pages previously
- * mapping the range to vmemmap_pages list so that they can be freed by
- * the caller.
+ * Remap the vmemmap virtual address range [@vmemmap_start, @vmemmap_end).
+ * Add pages previously mapping the range to vmemmap_pages list so that
+ * they can be freed by the caller.
*/
- ret = vmemmap_remap_free(vmemmap_start, vmemmap_end, vmemmap_reuse,
+ ret = vmemmap_remap_free(vmemmap_start, vmemmap_end,
+ vmemmap_head, vmemmap_tail,
vmemmap_pages, flags);
+out:
if (ret) {
static_branch_dec(&hugetlb_optimize_vmemmap_key);
folio_clear_hugetlb_vmemmap_optimized(folio);
@@ -632,21 +588,19 @@ void hugetlb_vmemmap_optimize_folio(const struct hstate *h, struct folio *folio)
static int hugetlb_vmemmap_split_folio(const struct hstate *h, struct folio *folio)
{
- unsigned long vmemmap_start = (unsigned long)&folio->page, vmemmap_end;
- unsigned long vmemmap_reuse;
+ unsigned long vmemmap_start, vmemmap_end;
if (!vmemmap_should_optimize_folio(h, folio))
return 0;
+ vmemmap_start = (unsigned long)&folio->page;
vmemmap_end = vmemmap_start + hugetlb_vmemmap_size(h);
- vmemmap_reuse = vmemmap_start;
- vmemmap_start += HUGETLB_VMEMMAP_RESERVE_SIZE;
/*
* Split PMDs on the vmemmap virtual address range [@vmemmap_start,
* @vmemmap_end]
*/
- return vmemmap_remap_split(vmemmap_start, vmemmap_end, vmemmap_reuse);
+ return vmemmap_remap_split(vmemmap_start, vmemmap_end);
}
static void __hugetlb_vmemmap_optimize_folios(struct hstate *h,
--
2.53.0
^ permalink raw reply related [flat|nested] 6+ messages in thread* [PATCH 6.18.y 4/5] hugetlb: remove VMEMMAP_SYNCHRONIZE_RCU
2026-09-03 16:59 ` [PATCH 6.18.y 1/5] mm: rework compound_head() for power-of-2 sizeof(struct page) Sasha Levin
2026-09-03 16:59 ` [PATCH 6.18.y 2/5] mm/hugetlb: defer vmemmap population for bootmem hugepages Sasha Levin
2026-09-03 16:59 ` [PATCH 6.18.y 3/5] mm/hugetlb: refactor code around vmemmap_walk Sasha Levin
@ 2026-09-03 16:59 ` Sasha Levin
2026-09-03 16:59 ` [PATCH 6.18.y 5/5] mm/hugetlb_vmemmap: fix __hugetlb_vmemmap_optimize_folios() Sasha Levin
3 siblings, 0 replies; 6+ messages in thread
From: Sasha Levin @ 2026-09-03 16:59 UTC (permalink / raw)
To: stable
Cc: Kiryl Shutsemau, Muchun Song, David Hildenbrand (Arm), Albert Ou,
Alexandre Ghiti, Baoquan He, Christoph Lameter, David Rientjes,
Frank van der Linden, Harry Yoo, Huacai Chen, Johannes Weiner,
Jonathan Corbet, Lorenzo Stoakes, Matthew Wilcox (Oracle),
Michal Hocko, Mike Rapoport, Oscar Salvador, Palmer Dabbelt,
Paul Walmsley, Roman Gushchin, Usama Arif, Vlastimil Babka,
WANG Xuerui, Zi Yan, Andrew Morton, Sasha Levin
From: Kiryl Shutsemau <kas@kernel.org>
[ Upstream commit 01b1d0ffb6f7f37f466033cf167959946309ed3d ]
The VMEMMAP_SYNCHRONIZE_RCU flag triggered synchronize_rcu() calls to
prevent a race between HVO remapping and page_ref_add_unless(). The race
could occur when a speculative PFN walker tried to modify the refcount on
a struct page that was in the process of being remapped to a fake head.
With fake heads eliminated, page_ref_add_unless() no longer needs RCU
protection.
Remove the flag and synchronize_rcu() calls.
Link: https://lkml.kernel.org/r/20260227194302.274384-15-kas@kernel.org
Signed-off-by: Kiryl Shutsemau <kas@kernel.org>
Reviewed-by: Muchun Song <muchun.song@linux.dev>
Reviewed-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Alexandre Ghiti <alex@ghiti.fr>
Cc: Baoquan He <bhe@redhat.com>
Cc: Christoph Lameter <cl@gentwo.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Frank van der Linden <fvdl@google.com>
Cc: Harry Yoo <harry.yoo@oracle.com>
Cc: Huacai Chen <chenhuacai@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Usama Arif <usamaarif642@gmail.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: WANG Xuerui <kernel@xen0n.name>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Stable-dep-of: 6e25c6a9c7ef ("mm/hugetlb_vmemmap: fix __hugetlb_vmemmap_optimize_folios()")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
mm/hugetlb_vmemmap.c | 20 ++++----------------
1 file changed, 4 insertions(+), 16 deletions(-)
diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
index 1f1c2ccca3159..f96d00a3ef2ee 100644
--- a/mm/hugetlb_vmemmap.c
+++ b/mm/hugetlb_vmemmap.c
@@ -45,8 +45,6 @@ struct vmemmap_remap_walk {
#define VMEMMAP_SPLIT_NO_TLB_FLUSH BIT(0)
/* Skip the TLB flush when we remap the PTE */
#define VMEMMAP_REMAP_NO_TLB_FLUSH BIT(1)
-/* synchronize_rcu() to avoid writes from page_ref_add_unless() */
-#define VMEMMAP_SYNCHRONIZE_RCU BIT(2)
unsigned long flags;
};
@@ -407,9 +405,6 @@ static int __hugetlb_vmemmap_restore_folio(const struct hstate *h,
if (!folio_test_hugetlb_vmemmap_optimized(folio))
return 0;
- if (flags & VMEMMAP_SYNCHRONIZE_RCU)
- synchronize_rcu();
-
vmemmap_start = (unsigned long)&folio->page;
vmemmap_end = vmemmap_start + hugetlb_vmemmap_size(h);
@@ -442,7 +437,7 @@ static int __hugetlb_vmemmap_restore_folio(const struct hstate *h,
*/
int hugetlb_vmemmap_restore_folio(const struct hstate *h, struct folio *folio)
{
- return __hugetlb_vmemmap_restore_folio(h, folio, VMEMMAP_SYNCHRONIZE_RCU);
+ return __hugetlb_vmemmap_restore_folio(h, folio, 0);
}
/**
@@ -465,14 +460,11 @@ long hugetlb_vmemmap_restore_folios(const struct hstate *h,
struct folio *folio, *t_folio;
long restored = 0;
long ret = 0;
- unsigned long flags = VMEMMAP_REMAP_NO_TLB_FLUSH | VMEMMAP_SYNCHRONIZE_RCU;
+ unsigned long flags = VMEMMAP_REMAP_NO_TLB_FLUSH;
list_for_each_entry_safe(folio, t_folio, folio_list, lru) {
if (folio_test_hugetlb_vmemmap_optimized(folio)) {
ret = __hugetlb_vmemmap_restore_folio(h, folio, flags);
- /* only need to synchronize_rcu() once for each batch */
- flags &= ~VMEMMAP_SYNCHRONIZE_RCU;
-
if (ret)
break;
restored++;
@@ -521,8 +513,6 @@ static int __hugetlb_vmemmap_optimize_folio(const struct hstate *h,
static_branch_inc(&hugetlb_optimize_vmemmap_key);
- if (flags & VMEMMAP_SYNCHRONIZE_RCU)
- synchronize_rcu();
/*
* Very Subtle
* If VMEMMAP_REMAP_NO_TLB_FLUSH is set, TLB flushing is not performed
@@ -582,7 +572,7 @@ void hugetlb_vmemmap_optimize_folio(const struct hstate *h, struct folio *folio)
{
LIST_HEAD(vmemmap_pages);
- __hugetlb_vmemmap_optimize_folio(h, folio, &vmemmap_pages, VMEMMAP_SYNCHRONIZE_RCU);
+ __hugetlb_vmemmap_optimize_folio(h, folio, &vmemmap_pages, 0);
free_vmemmap_page_list(&vmemmap_pages);
}
@@ -610,7 +600,7 @@ static void __hugetlb_vmemmap_optimize_folios(struct hstate *h,
struct folio *folio;
int nr_to_optimize;
LIST_HEAD(vmemmap_pages);
- unsigned long flags = VMEMMAP_REMAP_NO_TLB_FLUSH | VMEMMAP_SYNCHRONIZE_RCU;
+ unsigned long flags = VMEMMAP_REMAP_NO_TLB_FLUSH;
nr_to_optimize = 0;
list_for_each_entry(folio, folio_list, lru) {
@@ -664,8 +654,6 @@ static void __hugetlb_vmemmap_optimize_folios(struct hstate *h,
int ret;
ret = __hugetlb_vmemmap_optimize_folio(h, folio, &vmemmap_pages, flags);
- /* only need to synchronize_rcu() once for each batch */
- flags &= ~VMEMMAP_SYNCHRONIZE_RCU;
/*
* Pages to be freed may have been accumulated. If we
--
2.53.0
^ permalink raw reply related [flat|nested] 6+ messages in thread* [PATCH 6.18.y 5/5] mm/hugetlb_vmemmap: fix __hugetlb_vmemmap_optimize_folios()
2026-09-03 16:59 ` [PATCH 6.18.y 1/5] mm: rework compound_head() for power-of-2 sizeof(struct page) Sasha Levin
` (2 preceding siblings ...)
2026-09-03 16:59 ` [PATCH 6.18.y 4/5] hugetlb: remove VMEMMAP_SYNCHRONIZE_RCU Sasha Levin
@ 2026-09-03 16:59 ` Sasha Levin
3 siblings, 0 replies; 6+ messages in thread
From: Sasha Levin @ 2026-09-03 16:59 UTC (permalink / raw)
To: stable
Cc: Muchun Song, Oscar Salvador, Frank van der Linden,
Aneesh Kumar K.V, David Hildenbrand, Liam R. Howlett,
Lorenzo Stoakes, Madhavan Srinivasan, Michael Ellerman,
Mike Rapoport (Microsoft), Nicholas Piggin, Oscar Salvador (SUSE),
Ritesh Harjani (IBM), Usama Arif, Vlastimil Babka, Andrew Morton,
Sasha Levin
From: Muchun Song <songmuchun@bytedance.com>
[ Upstream commit 6e25c6a9c7eff141ecfc966ecdb7801db2a8810e ]
__hugetlb_vmemmap_optimize_folios() uses incorrect arguments when handling
bootmem HugeTLB folios.
The section number passed to register_page_bootmem_memmap() is derived
from the vmemmap virtual address of folio->page instead of the folio PFN,
so the bootmem memmap metadata can be registered against the wrong
section. The helper is also given HUGETLB_VMEMMAP_RESERVE_SIZE even
though it expects a page count, not a size in bytes. In addition, the
write-protect range is based on pages_per_huge_page(h), which does not
cover the full HugeTLB vmemmap area and can leave part of the shared tail
vmemmap mapping writable.
Fix the section lookup to use folio_pfn(folio), use
HUGETLB_VMEMMAP_RESERVE_PAGES when registering the reserved memmap pages,
and use hugetlb_vmemmap_size(h) for the write-protect range.
Link: https://lore.kernel.org/20260612035903.2468601-3-songmuchun@bytedance.com
Fixes: 752fe17af693 ("mm/hugetlb: add pre-HVO framework")
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: Oscar Salvador <osalvador@suse.de>
Reviewed-by: Frank van der Linden <fvdl@google.com>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Mike Rapoport (Microsoft) <rppt@kernel.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Oscar Salvador (SUSE) <osalvador@kernel.org>
Cc: "Ritesh Harjani (IBM)" <ritesh.list@gmail.com>
Cc: Usama Arif <usama.arif@linux.dev>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
mm/hugetlb_vmemmap.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
index f96d00a3ef2ee..0afacf93ca4cd 100644
--- a/mm/hugetlb_vmemmap.c
+++ b/mm/hugetlb_vmemmap.c
@@ -615,12 +615,12 @@ static void __hugetlb_vmemmap_optimize_folios(struct hstate *h,
* mirrored tail page structs RO.
*/
spfn = (unsigned long)&folio->page;
- epfn = spfn + pages_per_huge_page(h);
+ epfn = spfn + hugetlb_vmemmap_size(h);
vmemmap_wrprotect_hvo(spfn, epfn, folio_nid(folio),
HUGETLB_VMEMMAP_RESERVE_SIZE);
- register_page_bootmem_memmap(pfn_to_section_nr(spfn),
+ register_page_bootmem_memmap(pfn_to_section_nr(folio_pfn(folio)),
&folio->page,
- HUGETLB_VMEMMAP_RESERVE_SIZE);
+ HUGETLB_VMEMMAP_RESERVE_PAGES);
continue;
}
--
2.53.0
^ permalink raw reply related [flat|nested] 6+ messages in thread