Andi Kleen wrote:
Would it be worth trying to do something like this?
Maybe. Shouldn't be very hard though - you just need to check if the VMA is
backed by an object and if yes don't call copy_page_range for it.
I think it just needs (untested)
I think you need to check for MAP_SHARED as well, because
MAP_PRIVATE mapping of a file could be modified in parent.
See patch I posted just now.
Also, do you need any special case for hugetlb?
Index: linux-2.6.13-rc5-misc/kernel/fork.c
===================================================================
--- linux-2.6.13-rc5-misc.orig/kernel/fork.c
+++ linux-2.6.13-rc5-misc/kernel/fork.c
@@ -265,7 +265,8 @@ static inline int dup_mmap(struct mm_str
rb_parent = &tmp->vm_rb;
mm->map_count++;
- retval = copy_page_range(mm, current->mm, tmp);
+ if (!file && !is_vm_hugetlb_page(vma))
+ retval = copy_page_range(mm, current->mm, tmp);
spin_unlock(&mm->page_table_lock);
if (tmp->vm_ops && tmp->vm_ops->open)
But I'm not sure it's a good idea in all cases. Would need a lot of
benchmarking at least.
Yep. I'm sure it must have come up in the past, and Linus
must have said something about best-for-most.
--
SUSE Labs, Novell Inc.
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