* + mm-sparse-vmemmap-switch-device-dax-to-shared-tail-vmemmap-pages-fix.patch added to mm-unstable branch
@ 2026-09-30 19:01 Andrew Morton
0 siblings, 0 replies; 2+ messages in thread
From: Andrew Morton @ 2026-09-30 19:01 UTC (permalink / raw)
To: mm-commits, muchun.song, akpm
The patch titled
Subject: fixup! mm/sparse-vmemmap: switch device DAX to shared tail vmemmap pages
has been added to the -mm mm-unstable branch. Its filename is
mm-sparse-vmemmap-switch-device-dax-to-shared-tail-vmemmap-pages-fix.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-sparse-vmemmap-switch-device-dax-to-shared-tail-vmemmap-pages-fix.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
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*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via various
branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there most days
------------------------------------------------------
From: Muchun Song <muchun.song@linux.dev>
Subject: fixup! mm/sparse-vmemmap: switch device DAX to shared tail vmemmap pages
Date: Wed, 30 Sep 2026 23:07:48 +0800
prep_compound_tail() makes PageCompound() true. Calling
__SetPageReserved() afterwards violates the PF_NO_COMPOUND policy and
triggers VM_BUG_ON_PGFLAGS() when CONFIG_DEBUG_VM_PGFLAGS is enabled.
Set PG_reserved before preparing the compound tail.
Link: https://lore.kernel.org/20260930150748.1134516-1-songmuchun@bytedance.com
Signed-off-by: Muchun Song <muchun.song@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Qi Zheng <qi.zheng@linux.dev>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Christophe Leroy <chleroy@kernel.org>
Cc: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Cc: Shrikanth Hegde <sshegde@linux.ibm.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Lance Yang <lance.yang@linux.dev>
---
mm/sparse-vmemmap.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/mm/sparse-vmemmap.c~mm-sparse-vmemmap-switch-device-dax-to-shared-tail-vmemmap-pages-fix
+++ a/mm/sparse-vmemmap.c
@@ -224,9 +224,9 @@ struct page __ref *vmemmap_shared_tail_p
atomic_set(&page->_mapcount, -1);
set_page_node(page, zone_to_nid(zone));
set_page_zone(page, zone_idx(zone));
- prep_compound_tail(page, NULL, order);
if (zone_is_zone_device(zone))
__SetPageReserved(page);
+ prep_compound_tail(page, NULL, order);
}
page = virt_to_page(addr);
_
Patches currently in -mm which might be from muchun.song@linux.dev are
mm-sparse-vmemmap-factor-out-shared-vmemmap-tail-page-allocation.patch
mm-sparse-vmemmap-allocate-shared-tail-page-array-dynamically.patch
mm-sparse-vmemmap-introduce-config_vmemmap_optimization.patch
mm-sparse-vmemmap-open-code-init_compound_tail.patch
mm-sparse-vmemmap-prepare-dax-vmemmap-population-for-compound-page-orders.patch
mm-sparse-vmemmap-set-compound-page-order-for-device-dax.patch
mm-sparse-vmemmap-switch-device-dax-to-shared-tail-vmemmap-pages.patch
mm-sparse-vmemmap-switch-device-dax-to-shared-tail-vmemmap-pages-fix.patch
mm-sparse-vmemmap-move-vmemmap-optimization-helpers-to-a-public-header.patch
powerpc-mm-switch-device-dax-to-shared-tail-vmemmap-pages.patch
powerpc-mm-switch-device-dax-to-shared-tail-vmemmap-pages-fix.patch
mm-sparse-vmemmap-drop-the-extra-tail-page-from-device-dax-reservation.patch
mm-sparse-vmemmap-drop-unused-section_nr_vmemmap_pages-arguments.patch
documentation-mm-update-dax-vmemmap-deduplication-docs.patch
mm-sparse-vmemmap-drop-vmemmap_populate_dax.patch
mm-sparse-vmemmap-support-device-dax-in-common-vmemmap-path.patch
mm-sparse-vmemmap-drop-device-dax-specific-population-path.patch
mm-sparse-vmemmap-remove-the-unused-ptpfn-argument.patch
mm-sparse-vmemmap-open-code-vmemmap_populate_address.patch
mm-mm_init-add-zone-mismatch-warning-during-page-init.patch
^ permalink raw reply [flat|nested] 2+ messages in thread* + mm-sparse-vmemmap-switch-device-dax-to-shared-tail-vmemmap-pages-fix.patch added to mm-unstable branch
@ 2026-09-28 4:45 Andrew Morton
0 siblings, 0 replies; 2+ messages in thread
From: Andrew Morton @ 2026-09-28 4:45 UTC (permalink / raw)
To: mm-commits, rppt, rdunlap, qi.zheng, osalvador, npiggin, mpe,
maddy, ljs, lance.yang, david, corbet, chleroy, muchun.song, akpm
The patch titled
Subject: mm-sparse-vmemmap-switch-device-dax-to-shared-tail-vmemmap-pages-fix
has been added to the -mm mm-unstable branch. Its filename is
mm-sparse-vmemmap-switch-device-dax-to-shared-tail-vmemmap-pages-fix.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-sparse-vmemmap-switch-device-dax-to-shared-tail-vmemmap-pages-fix.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via various
branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there most days
------------------------------------------------------
From: Muchun Song <muchun.song@linux.dev>
Subject: mm-sparse-vmemmap-switch-device-dax-to-shared-tail-vmemmap-pages-fix
Date: Mon, 28 Sep 2026 12:41:48 +0800
Each PTE mapping the shared device DAX tail page takes a page reference.
A sufficiently large range could therefore cycle the reference count back
to zero if population were allowed to continue after it became
non-positive.
Use try_get_page() so further mappings fail once the reference count is no
longer positive. The section population error path tears down mappings
created for the failed section, while the warning makes this currently
impractical limit visible.
Link: https://lore.kernel.org/20260928044148.3300333-1-songmuchun@bytedance.com
Signed-off-by: Muchun Song <muchun.song@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Qi Zheng <qi.zheng@linux.dev>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Christophe Leroy <chleroy@kernel.org>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Lance Yang <lance.yang@linux.dev>
---
mm/sparse-vmemmap.c | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)
--- a/mm/sparse-vmemmap.c~mm-sparse-vmemmap-switch-device-dax-to-shared-tail-vmemmap-pages-fix
+++ a/mm/sparse-vmemmap.c
@@ -286,14 +286,18 @@ static pte_t * __meminit vmemmap_pte_pop
/*
* When a PTE/PMD entry is freed from the init_mm
* there's a free_pages() call to this page allocated
- * above. Thus this get_page() is paired with the
+ * above. Thus this try_get_page() is paired with the
* put_page_testzero() on the freeing path.
* This can only called by certain ZONE_DEVICE path,
* and through vmemmap_populate_compound_pages() when
* slab is available.
+ *
+ * Use try_get_page() to prevent the shared page refcount
+ * from overflowing.
*/
- if (flags & VMEMMAP_POPULATE_DAX)
- get_page(pfn_to_page(ptpfn));
+ if ((flags & VMEMMAP_POPULATE_DAX) &&
+ !try_get_page(pfn_to_page(ptpfn)))
+ return NULL;
}
entry = pfn_pte(ptpfn, PAGE_KERNEL);
set_pte_at(&init_mm, addr, pte, entry);
_
Patches currently in -mm which might be from muchun.song@linux.dev are
mm-sparse-vmemmap-factor-out-shared-vmemmap-tail-page-allocation.patch
mm-sparse-vmemmap-allocate-shared-tail-page-array-dynamically.patch
mm-sparse-vmemmap-introduce-config_vmemmap_optimization.patch
mm-sparse-vmemmap-open-code-init_compound_tail.patch
mm-sparse-vmemmap-prepare-dax-vmemmap-population-for-compound-page-orders.patch
mm-sparse-vmemmap-set-compound-page-order-for-device-dax.patch
mm-sparse-vmemmap-switch-device-dax-to-shared-tail-vmemmap-pages.patch
mm-sparse-vmemmap-switch-device-dax-to-shared-tail-vmemmap-pages-fix.patch
mm-sparse-vmemmap-move-vmemmap-optimization-helpers-to-a-public-header.patch
powerpc-mm-switch-device-dax-to-shared-tail-vmemmap-pages.patch
mm-sparse-vmemmap-drop-the-extra-tail-page-from-device-dax-reservation.patch
mm-sparse-vmemmap-drop-unused-section_nr_vmemmap_pages-arguments.patch
documentation-mm-update-dax-vmemmap-deduplication-docs.patch
^ permalink raw reply [flat|nested] 2+ messages in thread
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2026-09-28 4:45 Andrew Morton
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