linux-kernel - [v11 PATCH 3/3] mm: unmap VM_PFNMAP mappings with optimized path

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Date:   Thu, 20 Sep 2018 01:03:41 +0800
From:   Yang Shi <yang.shi@...ux.alibaba.com>
To:     mhocko@...nel.org, willy@...radead.org, ldufour@...ux.vnet.ibm.com,
        vbabka@...e.cz, kirill@...temov.name, akpm@...ux-foundation.org
Cc:     dave.hansen@...el.com, oleg@...hat.com, srikar@...ux.vnet.ibm.com,
        yang.shi@...ux.alibaba.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: [v11 PATCH 3/3] 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>
Reviewed-by: Matthew Wilcox <willy@...radead.org>
Signed-off-by: Yang Shi <yang.shi@...ux.alibaba.com>
---
 mm/mmap.c | 9 ---------
 1 file changed, 9 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index 490340e..847a17d 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2771,15 +2771,6 @@ static int __do_munmap(struct mm_struct *mm, unsigned long start, size_t len,
 				munlock_vma_pages_all(tmp);
 			}
 
-			/*
-			 * Unmapping vmas, which have VM_HUGETLB or VM_PFNMAP,
-			 * need get done with write mmap_sem held since they may
-			 * update vm_flags.
-			 */
-			if (downgrade &&
-			    (tmp->vm_flags & VM_PFNMAP))
-				downgrade = false;
-
 			tmp = tmp->vm_next;
 		}
 	}
-- 
1.8.3.1