linux-kernel - [PATCH 02/19] mm: Drop is_huge_zero

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Message-ID: <20240809160909.1023470-3-peterx@redhat.com>
Date: Fri,  9 Aug 2024 12:08:52 -0400
From: Peter Xu <peterx@...hat.com>
To: linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Cc: Sean Christopherson <seanjc@...gle.com>,
	Oscar Salvador <osalvador@...e.de>,
	Jason Gunthorpe <jgg@...dia.com>,
	Axel Rasmussen <axelrasmussen@...gle.com>,
	linux-arm-kernel@...ts.infradead.org,
	x86@...nel.org,
	peterx@...hat.com,
	Will Deacon <will@...nel.org>,
	Gavin Shan <gshan@...hat.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Zi Yan <ziy@...dia.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Ingo Molnar <mingo@...hat.com>,
	Alistair Popple <apopple@...dia.com>,
	Borislav Petkov <bp@...en8.de>,
	David Hildenbrand <david@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	kvm@...r.kernel.org,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Alex Williamson <alex.williamson@...hat.com>,
	Yan Zhao <yan.y.zhao@...el.com>,
	Matthew Wilcox <willy@...radead.org>,
	"Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>
Subject: [PATCH 02/19] mm: Drop is_huge_zero_pud()

It constantly returns false since 2017.  One assertion is added in 2019 but
it should never have triggered, IOW it means what is checked should be
asserted instead.

If it didn't exist for 7 years maybe it's good idea to remove it and only
add it when it comes.

Cc: Matthew Wilcox <willy@...radead.org>
Cc: Aneesh Kumar K.V <aneesh.kumar@...ux.ibm.com>
Signed-off-by: Peter Xu <peterx@...hat.com>
---
 include/linux/huge_mm.h | 10 ----------
 mm/huge_memory.c        | 13 +------------
 2 files changed, 1 insertion(+), 22 deletions(-)

diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 6370026689e0..2121060232ce 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -421,11 +421,6 @@ static inline bool is_huge_zero_pmd(pmd_t pmd)
 	return pmd_present(pmd) && READ_ONCE(huge_zero_pfn) == pmd_pfn(pmd);
 }
 
-static inline bool is_huge_zero_pud(pud_t pud)
-{
-	return false;
-}
-
 struct folio *mm_get_huge_zero_folio(struct mm_struct *mm);
 void mm_put_huge_zero_folio(struct mm_struct *mm);
 
@@ -566,11 +561,6 @@ static inline bool is_huge_zero_pmd(pmd_t pmd)
 	return false;
 }
 
-static inline bool is_huge_zero_pud(pud_t pud)
-{
-	return false;
-}
-
 static inline void mm_put_huge_zero_folio(struct mm_struct *mm)
 {
 	return;
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 0aafd26d7a53..39c401a62e87 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1245,10 +1245,8 @@ static void insert_pfn_pud(struct vm_area_struct *vma, unsigned long addr,
 	ptl = pud_lock(mm, pud);
 	if (!pud_none(*pud)) {
 		if (write) {
-			if (pud_pfn(*pud) != pfn_t_to_pfn(pfn)) {
-				WARN_ON_ONCE(!is_huge_zero_pud(*pud));
+			if (WARN_ON_ONCE(pud_pfn(*pud) != pfn_t_to_pfn(pfn)))
 				goto out_unlock;
-			}
 			entry = pud_mkyoung(*pud);
 			entry = maybe_pud_mkwrite(pud_mkdirty(entry), vma);
 			if (pudp_set_access_flags(vma, addr, pud, entry, 1))
@@ -1496,15 +1494,6 @@ int copy_huge_pud(struct mm_struct *dst_mm, struct mm_struct *src_mm,
 	if (unlikely(!pud_trans_huge(pud) && !pud_devmap(pud)))
 		goto out_unlock;
 
-	/*
-	 * When page table lock is held, the huge zero pud should not be
-	 * under splitting since we don't split the page itself, only pud to
-	 * a page table.
-	 */
-	if (is_huge_zero_pud(pud)) {
-		/* No huge zero pud yet */
-	}
-
 	/*
 	 * TODO: once we support anonymous pages, use
 	 * folio_try_dup_anon_rmap_*() and split if duplicating fails.
-- 
2.45.0