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    SubjectRe: [patch 1/3 take2] smaps: extract pte walker from smaps code
    On Wed, Feb 07, 2007 at 03:29:34PM +0900, Paul Mundt wrote:
    > On Tue, Feb 06, 2007 at 10:15:47PM -0800, David Rientjes wrote:
    > > Extracts the page table entry walker from the smaps-specific code in
    > > fs/proc/task_mmu.c. This will be used later for clearing the reference
    > > bits on pages to measure the number of pages accessed over a time period
    > > through /proc/pid/smaps.
    > >
    > I like the general idea of this patch set, however..
    > > Since the PTE walker is now extracted from the smaps code,
    > > smaps_pte_func() is invoked for each PTE in the VMA. Its behavior is
    > > identical to the existing implementation, except it is slightly slower
    > > because each PTE now invokes a function call.
    > >
    > Perhaps this is something that needs to be looked at more closely and
    > made more generic? There are many ranged page table walkers that aren't
    > so performance critical that the function call cost would cause too much
    > pain. ioremap_page_range() comes to mind, and there's bound to be others.
    > This would also help people to get the pte map/unmap right, which seems
    > to pop up from time to time as well..

    I've been looking at a similar refactoring of other code and I think
    the way to go is a callback per block-of-PTEs with start and end
    pointers. That gets rid of most of the call indirection overhead.

    Mathematics is the supreme nostalgia of our time.
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