linux-kernel - [PATCH v7 2/9] mm: Introduce vma_is_special

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Message-Id: <20200324201123.3118-3-thomas_os@shipmail.org>
Date:   Tue, 24 Mar 2020 21:11:16 +0100
From:   Thomas Hellström (VMware) 
        <thomas_os@...pmail.org>
To:     linux-mm@...ck.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Cc:     pv-drivers@...are.com, linux-graphics-maintainer@...are.com,
        "Thomas Hellstrom (VMware)" <thomas_os@...pmail.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Ralph Campbell <rcampbell@...dia.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Christian König <christian.koenig@....com>,
        Dan Williams <dan.j.williams@...el.com>
Subject: [PATCH v7 2/9] mm: Introduce vma_is_special_huge

From: "Thomas Hellstrom (VMware)" <thomas_os@...pmail.org>

For VM_PFNMAP and VM_MIXEDMAP vmas that want to support transhuge pages
and -page table entries, introduce vma_is_special_huge() that takes the
same codepaths as vma_is_dax().

The use of "special" follows the definition in memory.c, vm_normal_page():
"Special" mappings do not wish to be associated with a "struct page"
(either it doesn't exist, or it exists but they don't want to touch it)

For PAGE_SIZE pages, "special" is determined per page table entry to be
able to deal with COW pages. But since we don't have huge COW pages,
we can classify a vma as either "special huge" or "normal huge".

Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Michal Hocko <mhocko@...e.com>
Cc: "Matthew Wilcox (Oracle)" <willy@...radead.org>
Cc: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc: Ralph Campbell <rcampbell@...dia.com>
Cc: "Jérôme Glisse" <jglisse@...hat.com>
Cc: "Christian König" <christian.koenig@....com>
Cc: Dan Williams <dan.j.williams@...el.com>
Signed-off-by: Thomas Hellstrom (VMware) <thomas_os@...pmail.org>
Acked-by: Christian König <christian.koenig@....com>
Acked-by: Andrew Morton <akpm@...ux-foundation.org>
---
 include/linux/mm.h | 17 +++++++++++++++++
 mm/huge_memory.c   |  6 +++---
 2 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index c54fb96cb1e6..bdd79a72bb42 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2867,6 +2867,23 @@ extern long copy_huge_page_from_user(struct page *dst_page,
 				const void __user *usr_src,
 				unsigned int pages_per_huge_page,
 				bool allow_pagefault);
+
+/**
+ * vma_is_special_huge - Are transhuge page-table entries considered special?
+ * @vma: Pointer to the struct vm_area_struct to consider
+ *
+ * Whether transhuge page-table entries are considered "special" following
+ * the definition in vm_normal_page().
+ *
+ * Return: true if transhuge page-table entries should be considered special,
+ * false otherwise.
+ */
+static inline bool vma_is_special_huge(const struct vm_area_struct *vma)
+{
+	return vma_is_dax(vma) || (vma->vm_file &&
+				   (vma->vm_flags & (VM_PFNMAP | VM_MIXEDMAP)));
+}
+
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE || CONFIG_HUGETLBFS */
 
 #ifdef CONFIG_DEBUG_PAGEALLOC
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 24ad53b4dfc0..19c8d462ab08 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1802,7 +1802,7 @@ int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
 	orig_pmd = pmdp_huge_get_and_clear_full(tlb->mm, addr, pmd,
 			tlb->fullmm);
 	tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
-	if (vma_is_dax(vma)) {
+	if (vma_is_special_huge(vma)) {
 		if (arch_needs_pgtable_deposit())
 			zap_deposited_table(tlb->mm, pmd);
 		spin_unlock(ptl);
@@ -2066,7 +2066,7 @@ int zap_huge_pud(struct mmu_gather *tlb, struct vm_area_struct *vma,
 	 */
 	pudp_huge_get_and_clear_full(tlb->mm, addr, pud, tlb->fullmm);
 	tlb_remove_pud_tlb_entry(tlb, pud, addr);
-	if (vma_is_dax(vma)) {
+	if (vma_is_special_huge(vma)) {
 		spin_unlock(ptl);
 		/* No zero page support yet */
 	} else {
@@ -2175,7 +2175,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
 		 */
 		if (arch_needs_pgtable_deposit())
 			zap_deposited_table(mm, pmd);
-		if (vma_is_dax(vma))
+		if (vma_is_special_huge(vma))
 			return;
 		page = pmd_page(_pmd);
 		if (!PageDirty(page) && pmd_dirty(_pmd))
-- 
2.21.1