[RFC,v10,3/3] mm: unmap VM_PFNMAP mappings with optimized path
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Message ID 1536957299-43536-4-git-send-email-yang.shi@linux.alibaba.com
State New
Headers show
Series
  • mm: zap pages with read mmap_sem in munmap for large mapping
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Commit Message

Yang Shi Sept. 14, 2018, 8:34 p.m. UTC
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@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>
---
 mm/mmap.c | 9 ---------
 1 file changed, 9 deletions(-)

Comments

Matthew Wilcox Sept. 15, 2018, 9:45 a.m. UTC | #1
On Sat, Sep 15, 2018 at 04:34:59AM +0800, Yang Shi wrote:
> 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@kernel.org>
> Cc: Vlastimil Babka <vbabka@suse.cz>
> Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>

Reviewed-by: Matthew Wilcox <willy@infradead.org>

Patch
diff mbox series

diff --git a/mm/mmap.c b/mm/mmap.c
index 991e066..04c1d3b 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;
 		}
 	}