linux-kernel - [RFC v9 PATCH 3/4] mm: unmap VM_HUGETLB mappings with optimized path

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Message-Id: <1536699493-69195-4-git-send-email-yang.shi@linux.alibaba.com>
Date:   Wed, 12 Sep 2018 04:58:12 +0800
From:   Yang Shi <yang.shi@...ux.alibaba.com>
To:     mhocko@...nel.org, willy@...radead.org, ldufour@...ux.vnet.ibm.com,
        vbabka@...e.cz, akpm@...ux-foundation.org, dave.hansen@...el.com,
        oleg@...hat.com, srikar@...ux.vnet.ibm.com
Cc:     yang.shi@...ux.alibaba.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: [RFC v9 PATCH 3/4] mm: unmap VM_HUGETLB mappings with optimized path

When unmapping VM_HUGETLB mappings, vm flags need to be updated. Since
the vmas have been detached, so it sounds safe to update vm flags with
read mmap_sem.

Cc: Michal Hocko <mhocko@...nel.org>
Cc: Vlastimil Babka <vbabka@...e.cz>
Signed-off-by: Yang Shi <yang.shi@...ux.alibaba.com>
---
 mm/mmap.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index 937d2f2..086f8b5 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2812,12 +2812,12 @@ static int do_munmap_zap_rlock(struct mm_struct *mm, unsigned long start,
 	}
 
 	/*
-	 * Unmapping vmas, which have VM_HUGETLB or VM_PFNMAP
+	 * Unmapping vmas, which have VM_PFNMAP
 	 * need get done with write mmap_sem held since they may update
 	 * vm_flags. Deal with such mappings with regular do_munmap() call.
 	 */
 	for (vma = start_vma; vma && vma->vm_start < end; vma = vma->vm_next) {
-		if (vma->vm_flags & (VM_HUGETLB | VM_PFNMAP))
+		if (vma->vm_flags & VM_PFNMAP)
 			goto regular_path;
 	}
 
-- 
1.8.3.1