[SRU][N:gke][PATCH 017/106] mm: thp: batch-collapse PMD with set_ptes()

[Tim Whisonant]

From: Ryan Roberts <ryan.roberts at arm.com>

BugLink: https://bugs.launchpad.net/bugs/2059316
BugLink: https://bugs.launchpad.net/bugs/2117098

Refactor __split_huge_pmd_locked() so that a present PMD can be collapsed
to PTEs in a single batch using set_ptes().

This should improve performance a little bit, but the real motivation is
to remove the need for the arm64 backend to have to fold the contpte
entries.  Instead, since the ptes are set as a batch, the contpte blocks
can be initially set up pre-folded (once the arm64 contpte support is
added in the next few patches).  This leads to noticeable performance
improvement during split.

Link: https://lkml.kernel.org/r/20240215103205.2607016-3-ryan.roberts@arm.com
Signed-off-by: Ryan Roberts <ryan.roberts at arm.com>
Acked-by: David Hildenbrand <david at redhat.com>
Cc: Alistair Popple <apopple at nvidia.com>
Cc: Andrey Ryabinin <ryabinin.a.a at gmail.com>
Cc: Ard Biesheuvel <ardb at kernel.org>
Cc: Barry Song <21cnbao at gmail.com>
Cc: Borislav Petkov (AMD) <bp at alien8.de>
Cc: Catalin Marinas <catalin.marinas at arm.com>
Cc: Dave Hansen <dave.hansen at linux.intel.com>
Cc: "H. Peter Anvin" <hpa at zytor.com>
Cc: Ingo Molnar <mingo at redhat.com>
Cc: James Morse <james.morse at arm.com>
Cc: John Hubbard <jhubbard at nvidia.com>
Cc: Kefeng Wang <wangkefeng.wang at huawei.com>
Cc: Marc Zyngier <maz at kernel.org>
Cc: Mark Rutland <mark.rutland at arm.com>
Cc: Matthew Wilcox (Oracle) <willy at infradead.org>
Cc: Thomas Gleixner <tglx at linutronix.de>
Cc: Will Deacon <will at kernel.org>
Cc: Yang Shi <shy828301 at gmail.com>
Cc: Zi Yan <ziy at nvidia.com>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
(cherry picked from commit 2bdba9868a4ffcb1492db7272f34b54387910177)
Signed-off-by: dann frazier <dann.frazier at canonical.com>
Acked-by: Brad Figg <bfigg at nvidia.com>
Acked-by: Noah Wager <noah.wager at canonical.com>
Acked-by: Jacob Martin <jacob.martin at canonical.com>
Signed-off-by: Brad Figg <bfigg at nvidia.com>
Signed-off-by: Tim Whisonant <tim.whisonant at canonical.com>
---
 mm/huge_memory.c | 58 +++++++++++++++++++++++++++---------------------
 1 file changed, 33 insertions(+), 25 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 7759b7a4934be..9aefc10156a18 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2564,15 +2564,16 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
 
 	pte = pte_offset_map(&_pmd, haddr);
 	VM_BUG_ON(!pte);
-	for (i = 0, addr = haddr; i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE) {
-		pte_t entry;
-		/*
-		 * Note that NUMA hinting access restrictions are not
-		 * transferred to avoid any possibility of altering
-		 * permissions across VMAs.
-		 */
-		if (freeze || pmd_migration) {
+
+	/*
+	 * Note that NUMA hinting access restrictions are not transferred to
+	 * avoid any possibility of altering permissions across VMAs.
+	 */
+	if (freeze || pmd_migration) {
+		for (i = 0, addr = haddr; i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE) {
+			pte_t entry;
 			swp_entry_t swp_entry;
+
 			if (write)
 				swp_entry = make_writable_migration_entry(
 							page_to_pfn(page + i));
@@ -2591,25 +2592,32 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
 				entry = pte_swp_mksoft_dirty(entry);
 			if (uffd_wp)
 				entry = pte_swp_mkuffd_wp(entry);
-		} else {
-			entry = mk_pte(page + i, READ_ONCE(vma->vm_page_prot));
-			if (write)
-				entry = pte_mkwrite(entry, vma);
-			if (!young)
-				entry = pte_mkold(entry);
-			/* NOTE: this may set soft-dirty too on some archs */
-			if (dirty)
-				entry = pte_mkdirty(entry);
-			if (soft_dirty)
-				entry = pte_mksoft_dirty(entry);
-			if (uffd_wp)
-				entry = pte_mkuffd_wp(entry);
+
+			VM_WARN_ON(!pte_none(ptep_get(pte + i)));
+			set_pte_at(mm, addr, pte + i, entry);
 		}
-		VM_BUG_ON(!pte_none(ptep_get(pte)));
-		set_pte_at(mm, addr, pte, entry);
-		pte++;
+	} else {
+		pte_t entry;
+
+		entry = mk_pte(page, READ_ONCE(vma->vm_page_prot));
+		if (write)
+			entry = pte_mkwrite(entry, vma);
+		if (!young)
+			entry = pte_mkold(entry);
+		/* NOTE: this may set soft-dirty too on some archs */
+		if (dirty)
+			entry = pte_mkdirty(entry);
+		if (soft_dirty)
+			entry = pte_mksoft_dirty(entry);
+		if (uffd_wp)
+			entry = pte_mkuffd_wp(entry);
+
+		for (i = 0; i < HPAGE_PMD_NR; i++)
+			VM_WARN_ON(!pte_none(ptep_get(pte + i)));
+
+		set_ptes(mm, haddr, pte, entry, HPAGE_PMD_NR);
 	}
-	pte_unmap(pte - 1);
+	pte_unmap(pte);
 
 	if (!pmd_migration)
 		folio_remove_rmap_pmd(folio, page, vma);
-- 
2.43.0