linux-kernel - [RFC v8 PATCH 5/5] mm: unmap VM_PFNMAP mappings with optimized path

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Date:   Thu, 16 Aug 2018 02:49:50 +0800
From:   Yang Shi <yang.shi@...ux.alibaba.com>
To:     mhocko@...nel.org, willy@...radead.org, ldufour@...ux.vnet.ibm.com,
        kirill@...temov.name, vbabka@...e.cz, akpm@...ux-foundation.org,
        peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
        alexander.shishkin@...ux.intel.com, jolsa@...hat.com,
        namhyung@...nel.org
Cc:     yang.shi@...ux.alibaba.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: [RFC v8 PATCH 5/5] mm: unmap VM_PFNMAP mappings with optimized path

When unmapping VM_PFNMAP 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 | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index 3b9f734..0a9960d 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2811,16 +2811,13 @@ static int do_munmap_zap_rlock(struct mm_struct *mm, unsigned long start,
 	}
 
 	/*
-	 * Unmapping vmas, which have:
-	 *   VM_PFNMAP or
-	 *   uprobes
-	 * need get done with write mmap_sem held since they may update
-	 * vm_flags. Deal with such mappings with regular do_munmap() call.
+	 * Unmapping vmas, which have uprobes 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_file &&
-		    has_uprobes(vma, vma->vm_start, vma->vm_end)) ||
-		    (vma->vm_flags & VM_PFNMAP))
+		if (vma->vm_file &&
+		    has_uprobes(vma, vma->vm_start, vma->vm_end))
 			goto regular_path;
 	}
 
-- 
1.8.3.1