linux-kernel - [PATCH 2/4] mm: introduce mm_forbids

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Date:	Wed, 22 Oct 2014 10:30:22 +0200
From:	Dominik Dingel <dingel@...ux.vnet.ibm.com>
To:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	Mel Gorman <mgorman@...e.de>, Michal Hocko <mhocko@...e.cz>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Dave Hansen <dave.hansen@...el.com>,
	Rik van Riel <riel@...hat.com>
Cc:	Andrea Arcangeli <aarcange@...hat.com>,
	Andy Lutomirski <luto@...capital.net>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Bob Liu <lliubbo@...il.com>,
	Christian Borntraeger <borntraeger@...ibm.com>,
	Cornelia Huck <cornelia.huck@...ibm.com>,
	Gleb Natapov <gleb@...nel.org>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Hugh Dickins <hughd@...gle.com>,
	Ingo Molnar <mingo@...nel.org>,
	Jianyu Zhan <nasa4836@...il.com>,
	Johannes Weiner <hannes@...xchg.org>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Konstantin Weitz <konstantin.weitz@...il.com>,
	kvm@...r.kernel.org, linux390@...ibm.com,
	linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Sasha Levin <sasha.levin@...cle.com>,
	Dominik Dingel <dingel@...ux.vnet.ibm.com>
Subject: [PATCH 2/4] mm: introduce mm_forbids_zeropage function

Add a new function stub to allow architectures to disable for
an mm_structthe backing of non-present, anonymous pages with
read-only empty zero pages.

Signed-off-by: Dominik Dingel <dingel@...ux.vnet.ibm.com>
---
 include/linux/mm.h | 4 ++++
 mm/huge_memory.c   | 2 +-
 mm/memory.c        | 2 +-
 3 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index cd33ae2..0a2022e 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -56,6 +56,10 @@ extern int sysctl_legacy_va_layout;
 #define __pa_symbol(x)  __pa(RELOC_HIDE((unsigned long)(x), 0))
 #endif
 
+#ifndef mm_forbids_zeropage
+#define mm_forbids_zeropage(X)  (0)
+#endif
+
 extern unsigned long sysctl_user_reserve_kbytes;
 extern unsigned long sysctl_admin_reserve_kbytes;
 
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index de98415..357a381 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -805,7 +805,7 @@ int do_huge_pmd_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
 		return VM_FAULT_OOM;
 	if (unlikely(khugepaged_enter(vma, vma->vm_flags)))
 		return VM_FAULT_OOM;
-	if (!(flags & FAULT_FLAG_WRITE) &&
+	if (!(flags & FAULT_FLAG_WRITE) && !mm_forbids_zeropage(mm) &&
 			transparent_hugepage_use_zero_page()) {
 		spinlock_t *ptl;
 		pgtable_t pgtable;
diff --git a/mm/memory.c b/mm/memory.c
index 64f82aa..f275a9d 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2640,7 +2640,7 @@ static int do_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
 		return VM_FAULT_SIGBUS;
 
 	/* Use the zero-page for reads */
-	if (!(flags & FAULT_FLAG_WRITE)) {
+	if (!(flags & FAULT_FLAG_WRITE) && !mm_forbids_zeropage(mm)) {
 		entry = pte_mkspecial(pfn_pte(my_zero_pfn(address),
 						vma->vm_page_prot));
 		page_table = pte_offset_map_lock(mm, pmd, address, &ptl);
-- 
1.8.5.5

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