mm/sparse-vmemmap: fix vmemmap accounting underflow

Patch series "mm: Fix vmemmap optimization accounting and initialization",
v8.

The series fixes several bugs in vmemmap optimization, mainly around
incorrect page accounting and memmap initialization in DAX and memory
hotplug paths.  It also fixes pageblock migratetype initialization and
struct page initialization for ZONE_DEVICE compound pages.

Patches 1-4 fix vmemmap accounting issues.  Patch 1 fixes an accounting
underflow in the section activation failure path by moving vmemmap page
accounting into the lower-level allocation and freeing helpers.  Patch 2
fixes incorrect altmap passing in the memory hotplug error path.  Patch 3
passes pgmap through memory deactivation paths so the teardown side can
determine whether vmemmap optimization was in effect.  Patch 4 uses that
information to account the optimized DAX vmemmap size correctly.

Patches 5-6 fix initialization issues in mm/mm_init.  One makes sure all
pageblocks in ZONE_DEVICE compound pages get their migratetype
initialized.  The other fixes a case where DAX memory hotplug reuses an
unoptimized early-section memmap while compound_nr_pages() still assumes
vmemmap optimization, leaving tail struct pages uninitialized.


This patch (of 6):

In section_activate(), if populate_section_memmap() fails, the error
handling path calls section_deactivate() to roll back the state.  This
causes a vmemmap accounting imbalance.

Since commit c3576889d87b ("mm: fix accounting of memmap pages"), memmap
pages are accounted for only after populate_section_memmap() succeeds. 
However, the failure path unconditionally calls section_deactivate(),
which decreases the vmemmap count.  Consequently, a failure in
populate_section_memmap() leads to an accounting underflow, incorrectly
reducing the system's tracked vmemmap usage.

Fix this more thoroughly by moving all accounting calls into the lower
level functions that actually perform the vmemmap allocation and freeing:

  - populate_section_memmap() accounts for newly allocated vmemmap pages -
depopulate_section_memmap() unaccounts when vmemmap is freed

This ensures proper accounting in all code paths, including error handling
and early section cases.

Link: https://lore.kernel.org/20260428081855.1249045-1-songmuchun@bytedance.com
Link: https://lore.kernel.org/20260428081855.1249045-2-songmuchun@bytedance.com
Fixes: c3576889d87b ("mm: fix accounting of memmap pages")
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Acked-by: Oscar Salvador <osalvador@suse.de>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Acked-by: Liam R. Howlett <liam@infradead.org>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Cc: Joao Martins <joao.m.martins@oracle.com>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

0 files changed, 0 insertions, 0 deletions