[merged mm-stable] mm-add-a-template-based-fast-path-for-zone-device-page-init.patch removed from -mm tree

[merged mm-stable] mm-add-a-template-based-fast-path-for-zone-device-page-init.patch removed from -mm tree

[Andrew Morton]

The quilt patch titled
     Subject: mm: add a template-based fast path for zone-device page init
has been removed from the -mm tree.  Its filename was
     mm-add-a-template-based-fast-path-for-zone-device-page-init.patch

This patch was dropped because it was merged into the mm-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: "Li Zhe" <lizhe.67@bytedance.com>
Subject: mm: add a template-based fast path for zone-device page init
Date: Mon, 31 Aug 2026 19:16:34 +0800

memmap_init_zone_device() repeats nearly identical head-page
initialization for each PFN.  Initialize the first real ZONE_DEVICE head
page through the existing path, copy that final state into a reusable
template, refresh the PFN-dependent fields in that template before each
copy, and copy it into the remaining destination pages.

Use the template path unconditionally.  The page_ref_set tracepoint is
primarily a debugging aid, while this code is still initializing struct
pages before they are handed out.  From the perspective of users of those
pages, the initialization-time refcount transitions are not part of the
observable page lifetime.

This means page_ref_set will no longer observe every initialization-time
refcount assignment for copied ZONE_DEVICE head pages.  The impact is
controlled because the final initialized struct page state is unchanged,
and keeping a separate non-template path only for this local tracepoint
observability would add complexity to the common path.

This patch accelerates head-page initialization.  The pfns_per_compound ==
1 case gets the full benefit here, compound tails are handled in the next
patch.

Tested in a VM with a 100 GB fsdax namespace device configured with
map=dev on Intel Ice Lake server.  This test exercises the nd_pmem rebind
path (pfns_per_compound == 1).

Test procedure:
Rebind the nd_pmem driver 30 times and collect the memmap initialization
time from the pr_debug() output of memmap_init_zone_device().

Base(v7.3-rc1):
  Average of rebinds for nd_pmem driver: 221.07 ms

With this patch and its prerequisites applied:
  Average of rebinds for nd_pmem driver: 155.00 ms

This reduces the average memmap initialization time measured during
rebind from 221.07 ms to 155.00 ms, or about 29.9%.

[lizhe.67@bytedance.com: whitespace fix, per Mike]
  Link: https://lore.kernel.org/20260903025806.70825-1-lizhe.67@bytedance.com
Link: https://lore.kernel.org/20260831111638.76012-4-lizhe.67@bytedance.com
Signed-off-by: Li Zhe <lizhe.67@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Balbir Singh <balbirs@nvidia.com>
Cc: "Borislav Petkov (AMD)" <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David Hildenbrand (Arm) <david@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Kees Cook <kees@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
---

 mm/mm_init.c |   37 ++++++++++++++++++++++++++++++++++---
 1 file changed, 34 insertions(+), 3 deletions(-)

--- a/mm/mm_init.c~mm-add-a-template-based-fast-path-for-zone-device-page-init
+++ a/mm/mm_init.c
@@ -1029,6 +1029,17 @@ static void __ref __init_zone_device_pag
 	}
 }
 
+static void zone_device_page_init_from_template(struct page *page,
+		unsigned long pfn, struct page *template)
+{
+	set_page_section_from_pfn(template, pfn);
+#ifdef WANT_PAGE_VIRTUAL
+	if (!is_highmem_idx(ZONE_DEVICE))
+		set_page_address(template, __va(pfn << PAGE_SHIFT));
+#endif
+	memcpy(page, template, sizeof(*page));
+}
+
 /*
  * With compound page geometry and when struct pages are stored in ram most
  * tail pages are reused. Consequently, the amount of unique struct pages to
@@ -1091,6 +1102,8 @@ void __ref memmap_init_zone_device(struc
 	unsigned long zone_idx = zone_idx(zone);
 	unsigned long start = jiffies;
 	int nid = pgdat->node_id;
+	struct page template;
+	struct page *page;
 
 	if (WARN_ON_ONCE(!pgmap || zone_idx != ZONE_DEVICE))
 		return;
@@ -1105,10 +1118,28 @@ void __ref memmap_init_zone_device(struc
 		nr_pages = end_pfn - start_pfn;
 	}
 
-	for (pfn = start_pfn; pfn < end_pfn; pfn += pfns_per_compound) {
-		struct page *page = pfn_to_page(pfn);
+	if (!nr_pages)
+		return;
 
-		__init_zone_device_page(page, pfn, zone_idx, nid, pgmap);
+	/*
+	 * Seed the reusable head-page template from the first real struct
+	 * page. The normal page-init and refcount helpers must operate on
+	 * a real memmap entry rather than a stack object.
+	 */
+	pfn = start_pfn;
+	page = pfn_to_page(pfn);
+	__init_zone_device_page(page, pfn, zone_idx, nid, pgmap);
+	memcpy(&template, page, sizeof(*page));
+	if (pfns_per_compound != 1)
+		memmap_init_compound(page, pfn, zone_idx, nid, pgmap,
+				     compound_nr_pages(pfn, altmap, pgmap));
+	pfn += pfns_per_compound;
+
+	/* Initialize the remaining head pages from template. */
+	for (; pfn < end_pfn; pfn += pfns_per_compound) {
+		page = pfn_to_page(pfn);
+
+		zone_device_page_init_from_template(page, pfn, &template);
 
 		if (IS_ALIGNED(pfn, PAGES_PER_SECTION))
 			cond_resched();
_

Patches currently in -mm which might be from lizhe.67@bytedance.com are

mm-hugetlb-fix-overbroad-mmu-notifiers-for-unshared-pmds.patch