linux-kernel - [RFC V2 14/37] mm, dmem: differentiate dmem-pmd and thp-pmd

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Date:   Mon,  7 Dec 2020 19:31:07 +0800
From:   yulei.kernel@...il.com
To:     linux-mm@...ck.org, akpm@...ux-foundation.org,
        linux-fsdevel@...r.kernel.org, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, naoya.horiguchi@....com,
        viro@...iv.linux.org.uk, pbonzini@...hat.com
Cc:     joao.m.martins@...cle.com, rdunlap@...radead.org,
        sean.j.christopherson@...el.com, xiaoguangrong.eric@...il.com,
        kernellwp@...il.com, lihaiwei.kernel@...il.com,
        Yulei Zhang <yuleixzhang@...cent.com>,
        Chen Zhuo <sagazchen@...cent.com>
Subject: [RFC V2 14/37] mm, dmem: differentiate dmem-pmd and thp-pmd

From: Yulei Zhang <yuleixzhang@...cent.com>

A dmem huge page is ultimately not a transparent huge page. As we
decided to use pmd_special() to distinguish dmem-pmd from thp-pmd,
we should make some slightly different semantics between pmd_special()
and pmd_trans_huge(), just as pmd_devmap() in upstream. This distinction
is especially important in some mm-core paths such as zap_pmd_range().

Explicitly mark the pmd_trans_huge() helpers that dmem needs by adding
pmd_special() checks. This method could be reused in many mm-core paths.

Signed-off-by: Chen Zhuo <sagazchen@...cent.com>
Signed-off-by: Yulei Zhang <yuleixzhang@...cent.com>
---
 arch/x86/include/asm/pgtable.h | 10 +++++++++-
 include/linux/pgtable.h        |  5 +++++
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index dd4aff6..6ce85d4 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -259,7 +259,7 @@ static inline int pmd_large(pmd_t pte)
 /* NOTE: when predicate huge page, consider also pmd_devmap, or use pmd_large */
 static inline int pmd_trans_huge(pmd_t pmd)
 {
-	return (pmd_val(pmd) & (_PAGE_PSE|_PAGE_DEVMAP)) == _PAGE_PSE;
+	return (pmd_val(pmd) & (_PAGE_PSE|_PAGE_DEVMAP|_PAGE_DMEM)) == _PAGE_PSE;
 }
 
 #ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
@@ -275,6 +275,14 @@ static inline int has_transparent_hugepage(void)
 	return boot_cpu_has(X86_FEATURE_PSE);
 }
 
+#ifdef CONFIG_ARCH_HAS_PTE_DMEM
+static inline int pmd_special(pmd_t pmd)
+{
+	return (pmd_val(pmd) & (_PAGE_SPECIAL | _PAGE_DMEM)) ==
+		(_PAGE_SPECIAL | _PAGE_DMEM);
+}
+#endif
+
 #ifdef CONFIG_ARCH_HAS_PTE_DEVMAP
 static inline int pmd_devmap(pmd_t pmd)
 {
diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index 9e65694..30342b8 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -1162,6 +1162,11 @@ static inline pmd_t pmd_mkdmem(pmd_t pmd)
 {
 	return pmd;
 }
+
+static inline int pmd_special(pmd_t pmd)
+{
+	return 0;
+}
 #endif
 
 #ifndef pmd_read_atomic
-- 
1.8.3.1