[Xen-devel] [PATCH 0/9] Add apply_to_page_range_batch() and use it

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

From: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>

I'm proposing this series for 2.6.39.

We've had apply_to_page_range() for a while, which is a general way to
apply a function to ptes across a range of addresses - including
allocating any missing parts of the pagetable as needed.  This logic
is replicated in a number of places throughout the kernel, but it
hasn't been widely replaced by this function, partly because of
concerns about the overhead of calling the function once per pte.

This series adds apply_to_page_range_batch() (and reimplements
apply_to_page_range() in terms of it), which calls the pte operation
function once per pte page, moving the inner loop into the callback
function.

apply_to_page_range(_batch) also calls its callback with lazy mmu
updates enabled, which allows batching of the operations in
environments where this is beneficial (ie, virtualization).  The only
caveat this introduces is callbacks can't expect to immediately see
the effects of the pte updates in memory.

Since this is effectively identical to the code in lib/ioremap.c and
mm/vmalloc.c (twice!), I replace their open-coded variants.  I'm sure
there are others places in the kernel which could do with this (I only
stumbled over ioremap by accident).

I also add a minor optimisation to vunmap_page_range() to use a
plain pte_clear() rather than the more expensive and unnecessary
ptep_get_and_clear().

Jeremy Fitzhardinge (9):
  mm: remove unused "token" argument from apply_to_page_range callback.
  mm: add apply_to_page_range_batch()
  ioremap: use apply_to_page_range_batch() for ioremap_page_range()
  vmalloc: use plain pte_clear() for unmaps
  vmalloc: use apply_to_page_range_batch() for vunmap_page_range()
  vmalloc: use apply_to_page_range_batch() for
    vmap_page_range_noflush()
  vmalloc: use apply_to_page_range_batch() in alloc_vm_area()
  xen/mmu: use apply_to_page_range_batch() in
    xen_remap_domain_mfn_range()
  xen/grant-table: use apply_to_page_range_batch()

 arch/x86/xen/grant-table.c |   30 +++++----
 arch/x86/xen/mmu.c         |   18 +++--
 include/linux/mm.h         |    9 ++-
 lib/ioremap.c              |   85 +++++++------------------
 mm/memory.c                |   57 ++++++++++++-----
 mm/vmalloc.c               |  150 ++++++++++++--------------------------------
 6 files changed, 140 insertions(+), 209 deletions(-)

-- 
1.7.3.4


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