linux-kernel - [RFC PATCH 15/24] mm/hugetlb: Use PG

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20200915125947.26204-16-songmuchun@bytedance.com>
Date:   Tue, 15 Sep 2020 20:59:38 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     corbet@....net, mike.kravetz@...cle.com, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, x86@...nel.org, hpa@...or.com,
        dave.hansen@...ux.intel.com, luto@...nel.org, peterz@...radead.org,
        viro@...iv.linux.org.uk, akpm@...ux-foundation.org,
        paulmck@...nel.org, mchehab+huawei@...nel.org,
        pawan.kumar.gupta@...ux.intel.com, rdunlap@...radead.org,
        oneukum@...e.com, anshuman.khandual@....com, jroedel@...e.de,
        almasrymina@...gle.com, rientjes@...gle.com
Cc:     linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        Muchun Song <songmuchun@...edance.com>
Subject: [RFC PATCH 15/24] mm/hugetlb: Use PG_slab to indicate split pmd

When we allocate hugetlb page from buddy, we may need split huge pmd
to pte. When we free the hugetlb page, we can merge pte to pmd. So
we need to distinguish whether the previous pmd has been split. The
page table is not allocated from slab. So we can reuse the PG_slab
to indicate that the pmd has been split.

Signed-off-by: Muchun Song <songmuchun@...edance.com>
---
 mm/hugetlb.c | 23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 5cc796dc3a0a..c42c27a12df2 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1629,6 +1629,25 @@ static void split_vmemmap_huge_page(struct page *head, pmd_t *pmd)
 	flush_tlb_kernel_range(start, addr);
 }
 
+static inline bool pmd_split(pmd_t *pmd)
+{
+	return PageSlab(pmd_page(*pmd));
+}
+
+static inline void set_pmd_split(pmd_t *pmd)
+{
+	/*
+	 * We should not use slab for page table allocation. So we can set
+	 * PG_slab to indicate that the pmd has been split.
+	 */
+	__SetPageSlab(pmd_page(*pmd));
+}
+
+static inline void clear_pmd_split(pmd_t *pmd)
+{
+	__ClearPageSlab(pmd_page(*pmd));
+}
+
 static void free_huge_page_vmemmap(struct hstate *h, struct page *head)
 {
 	pmd_t *pmd;
@@ -1645,6 +1664,7 @@ static void free_huge_page_vmemmap(struct hstate *h, struct page *head)
 	if (vmemmap_pmd_huge(pmd)) {
 		VM_BUG_ON(!nr_pgtable(h));
 		split_vmemmap_huge_page(head, pmd);
+		set_pmd_split(pmd);
 	}
 
 	remap_huge_page_pmd_vmemmap(h, pmd, (unsigned long)head, &free_pages,
@@ -1718,11 +1738,12 @@ static void alloc_huge_page_vmemmap(struct hstate *h, struct page *head)
 	spin_lock(ptl);
 	remap_huge_page_pmd_vmemmap(h, pmd, (unsigned long)head, &remap_pages,
 				    __remap_huge_page_pte_vmemmap);
-	if (!freed_vmemmap_hpage_dec(pmd_page(*pmd))) {
+	if (!freed_vmemmap_hpage_dec(pmd_page(*pmd)) && pmd_split(pmd)) {
 		/*
 		 * Todo:
 		 * Merge pte to huge pmd if it has ever been split.
 		 */
+		clear_pmd_split(pmd);
 	}
 	spin_unlock(ptl);
 }
-- 
2.20.1