Messages in this thread | | | Date | Fri, 26 Aug 2005 00:35:07 +1000 | From | Nick Piggin <> | Subject | Re: process creation time increases linearly with shmem |
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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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