linux-kernel - [PATCH v2 4/5] mm/hugetlb: use PMD page lock to protect CONT-PTE entries

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Message-Id: <88c8a8c68d87429f0fc48e81100f19b71f6e664f.1661240170.git.baolin.wang@linux.alibaba.com>
Date:   Tue, 23 Aug 2022 15:50:04 +0800
From:   Baolin Wang <baolin.wang@...ux.alibaba.com>
To:     akpm@...ux-foundation.org, songmuchun@...edance.com,
        mike.kravetz@...cle.com
Cc:     baolin.wang@...ux.alibaba.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2 4/5] mm/hugetlb: use PMD page lock to protect CONT-PTE entries

Considering the pmd entries of a CONT-PMD hugetlb can not span on
multiple PMDs, we can change to use the PMD page lock, which can
be much finer grain that lock in the mm.

Signed-off-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
---
 include/linux/hugetlb.h | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 3a96f67..d4803a89 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -892,9 +892,17 @@ static inline gfp_t htlb_modify_alloc_mask(struct hstate *h, gfp_t gfp_mask)
 static inline spinlock_t *huge_pte_lockptr(struct hstate *h,
 					   struct mm_struct *mm, pte_t *pte)
 {
-	VM_BUG_ON(huge_page_size(h) == PAGE_SIZE);
+	unsigned long hp_size = huge_page_size(h);
 
-	if (huge_page_size(h) == PMD_SIZE) {
+	VM_BUG_ON(hp_size == PAGE_SIZE);
+
+	/*
+	 * Considering CONT-PMD size hugetlb, since the CONT-PMD entry
+	 * can not span multiple PMDs, then we can use the fine grained
+	 * PMD page lock.
+	 */
+	if (hp_size == PMD_SIZE ||
+	    (hp_size > PMD_SIZE && hp_size < PUD_SIZE)) {
 		return pmd_lockptr(mm, (pmd_t *) pte);
 	} else if (huge_page_size(h) < PMD_SIZE) {
 		unsigned long mask = ~(PTRS_PER_PTE * sizeof(pte_t) - 1);
-- 
1.8.3.1