linux-kernel - copy_page_range() with VM

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Message-ID: <87a5b0800803100926t1e4a1bb3t905d02d4c311d5e@mail.gmail.com>
Date:	Mon, 10 Mar 2008 16:26:02 +0000
From:	"Will Newton" <will.newton@...il.com>
To:	LKML <linux-kernel@...r.kernel.org>
Subject: copy_page_range() with VM_LOCKED

Hi all,

In order to optimize fork performance copy_page_range avoids copying
page tables under certain circumstances:

        if (!(vma->vm_flags &
(VM_HUGETLB|VM_NONLINEAR|VM_PFNMAP|VM_INSERTPAGE))) {
                if (!vma->anon_vma)
                        return 0;
        }

I have a VM_LOCKED vma that I would really, really like not to fault
on, but because copy_page_range does not copy the page tables of the
vma I do end up faulting in my VM_LOCKED vma. Now as far as I'm aware
mmap with MAP_LOCKED only promises the page will not be paged out, not
that the page will never fault but I would like to get that behaviour.

Would it be possible to add VM_LOCKED to the above conditional so
copy_page_range would always copy VM_LOCKED vma page tables or would
that be considered insane and broken?

Thanks,
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