linux-kernel - [PATCH 2/3] mm: Add generic helper to hint a large folio

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Message-Id: <20250506050056.59250-3-dev.jain@arm.com>
Date: Tue,  6 May 2025 10:30:55 +0530
From: Dev Jain <dev.jain@....com>
To: akpm@...ux-foundation.org
Cc: Liam.Howlett@...cle.com,
	lorenzo.stoakes@...cle.com,
	vbabka@...e.cz,
	jannh@...gle.com,
	pfalcato@...e.de,
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	linux-kernel@...r.kernel.org,
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	peterx@...hat.com,
	ryan.roberts@....com,
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	Dev Jain <dev.jain@....com>
Subject: [PATCH 2/3] mm: Add generic helper to hint a large folio

To use PTE batching, we want to determine whether the folio mapped by
the PTE is large, thus requiring the use of vm_normal_folio(). We want
to avoid the cost of vm_normal_folio() if the code path doesn't already
require the folio. For arm64, pte_batch_hint() does the job. To generalize
this hint, add a helper which will determine whether two consecutive PTEs
point to consecutive PFNs, in which case there is a high probability that
the underlying folio is large.

Signed-off-by: Dev Jain <dev.jain@....com>
---
 include/linux/pgtable.h | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index b50447ef1c92..28e21fcc7837 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -369,6 +369,22 @@ static inline pgd_t pgdp_get(pgd_t *pgdp)
 }
 #endif
 
+/* Caller must ensure that ptep + 1 exists */
+static inline bool maybe_contiguous_pte_pfns(pte_t *ptep, pte_t pte)
+{
+	pte_t *next_ptep, next_pte;
+
+	if (pte_batch_hint(ptep, pte) != 1)
+		return true;
+
+	next_ptep = ptep + 1;
+	next_pte = ptep_get(next_ptep);
+	if (!pte_present(next_pte))
+		return false;
+
+	return unlikely(pte_pfn(next_pte) - pte_pfn(pte) == PAGE_SIZE);
+}
+
 #ifndef __HAVE_ARCH_PTEP_TEST_AND_CLEAR_YOUNG
 static inline int ptep_test_and_clear_young(struct vm_area_struct *vma,
 					    unsigned long address,
-- 
2.30.2