linux-kernel - [PATCH] mm/mprotect: reduce Committed_AS if memory protection is changed to PROT

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Date:   Tue, 26 Apr 2022 19:27:05 +0800
From:   liusongtang <liusongtang@...wei.com>
To:     <akpm@...ux-foundation.org>
CC:     <liusongtang@...wei.com>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>, <nixiaoming@...wei.com>,
        <young.liuyang@...wei.com>, <wangkefeng@...wei.com>
Subject: [PATCH] mm/mprotect: reduce Committed_AS if memory protection is changed to PROT_NONE

If PROT_WRITE is set, the size of vm area will be added to Committed_AS.
However, if memory protection is changed to PROT_NONE,
the corresponding physical memory will not be used, but Committed_AS still
count the size of the PROT_NONE memory.

This patch reduce Committed_AS and free the corresponding memory if
memory protection is changed to PROT_NONE.

Signed-off-by: liusongtang <liusongtang@...wei.com>
---
 mm/mprotect.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/mm/mprotect.c b/mm/mprotect.c
index b69ce7a..c3121e6 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -497,6 +497,12 @@ mprotect_fixup(struct vm_area_struct *vma, struct vm_area_struct **pprev,
 	}
 
 success:
+	if ((newflags & (VM_READ | VM_WRITE | VM_EXEC | VM_LOCKED | VM_ACCOUNT)) == VM_ACCOUNT) {
+		zap_page_range(vma, start, end - start);
+		newflags &= ~VM_ACCOUNT;
+		vm_unacct_memory((end - start) >> PAGE_SHIFT);
+	}
+
 	/*
 	 * vm_flags and vm_page_prot are protected by the mmap_lock
 	 * held in write mode.
-- 
2.12.3