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Subject[PATCH] Don't needlessly dirty mlocked pages when initially faulting them in.
Date
make_pages_present() is dirtying mlocked pages if the VMA is writable, even
though it shouldn't, by telling get_user_pages() to simulate a write fault.

A simple way to test this is to mlock a multi-GB file, and then sync.
The sync will take a long time.

As far as I can see, it should be safe to just not simulate a write fault.

Signed-off-by: Suleiman Souhlal <suleiman@google.com>
---
mm/memory.c | 5 ++---
1 files changed, 2 insertions(+), 3 deletions(-)
diff --git a/mm/memory.c b/mm/memory.c
index f64cbf9..f43c9e8 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2664,18 +2664,17 @@ #endif /* __PAGETABLE_PMD_FOLDED */

int make_pages_present(unsigned long addr, unsigned long end)
{
- int ret, len, write;
+ int ret, len;
struct vm_area_struct * vma;

vma = find_vma(current->mm, addr);
if (!vma)
return -1;
- write = (vma->vm_flags & VM_WRITE) != 0;
BUG_ON(addr >= end);
BUG_ON(end > vma->vm_end);
len = (end+PAGE_SIZE-1)/PAGE_SIZE-addr/PAGE_SIZE;
ret = get_user_pages(current, current->mm, addr,
- len, write, 0, NULL, NULL);
+ len, 0, 0, NULL, NULL);
if (ret < 0)
return ret;
return ret == len ? 0 : -1;
--
1.4.2
-
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