[PATCH 24/49] mm/sparse-vmemmap: initialize shared tail vmemmap page upon allocation

[Muchun Song]

Previously, the shared vmemmap tail page allocated in vmemmap_get_tail()
was intentionally left uninitialized. This was because the subsequent
memmap_init_range() would unconditionally overwrite any initialization done
here, forcing subsystems (like HugeTLB) to compensate and perform the
initialization later in their own specific routines (e.g., hugetlb_vmemmap_init()).

Thanks to the previous patch, memmap_init_range() is now aware of the
section's compound page order and safely skips the redundant initialization
for these optimizable compound vmemmap pages.

Because the overwrite issue is resolved, we can now fully initialize the
shared tail pages (via init_compound_tail()) immediately upon allocation
in vmemmap_get_tail(). This simplifies the initialization flow and removes
the need to defer this work to specific subsystems.

Note that the initialization logic in hugetlb_vmemmap_init() is not removed
yet. It will be completely removed once HugeTLB switches to the new memory
section compound page order mechanism.

Signed-off-by: Muchun Song <songmuchun at bytedance.com>
---
 mm/sparse-vmemmap.c | 11 ++---------
 1 file changed, 2 insertions(+), 9 deletions(-)

diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
index 9f70559df4e8..2a6c3c82f9f5 100644
--- a/mm/sparse-vmemmap.c
+++ b/mm/sparse-vmemmap.c
@@ -340,18 +340,11 @@ static __meminit struct page *vmemmap_get_tail(unsigned int order, struct zone *
 	if (tail)
 		return tail;
 
-	/*
-	 * Only allocate the page, but do not initialize it.
-	 *
-	 * Any initialization done here will be overwritten by memmap_init().
-	 *
-	 * hugetlb_vmemmap_init() will take care of initialization after
-	 * memmap_init().
-	 */
-
 	p = vmemmap_alloc_block_zero(PAGE_SIZE, node);
 	if (!p)
 		return NULL;
+	for (int i = 0; i < PAGE_SIZE / sizeof(struct page); i++)
+		init_compound_tail(p + i, NULL, order, zone);
 
 	tail = virt_to_page(p);
 	zone->vmemmap_tails[idx] = tail;
-- 
2.20.1