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mempolicy: use MPOL_F_LOCAL to Indicate Preferred Local Policy

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Now that we're using "preferred local" policy for system default, we need to
make this as fast as possible.  Because of the variable size of the mempolicy
structure [based on size of nodemasks], the preferred_node may be in a
different cacheline from the mode.  This can result in accessing an extra
cacheline in the normal case of system default policy.  Suspect this is the
cause of an observed 2-3% slowdown in page fault testing relative to kernel
without this patch series.

To alleviate this, use an internal mode flag, MPOL_F_LOCAL in the mempolicy
flags member which is guaranteed [?] to be in the same cacheline as the mode
itself.

Verified that reworked mempolicy now performs slightly better on 25-rc8-mm1
for both anon and shmem segments with system default and vma [preferred local]
policy.

Signed-off-by: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Christoph Lameter <clameter@sgi.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Lee Schermerhorn
2008-04-28 02:13:21 -07:00
committed by Linus Torvalds
parent 53f2556b67
commit fc36b8d3d8
3 changed files with 28 additions and 31 deletions
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11
Documentation/vm/numa_memory_policy.txt
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@@ -176,12 +176,11 @@ Components of Memory Policies
containing the cpu where the allocation takes place.
Internally, the Preferred policy uses a single node--the
preferred_node member of struct mempolicy. A "distinguished
value of this preferred_node, currently '-1', is interpreted
as "the node containing the cpu where the allocation takes
place"--local allocation. "Local" allocation policy can be
viewed as a Preferred policy that starts at the node containing
the cpu where the allocation takes place.
preferred_node member of struct mempolicy. When the internal
mode flag MPOL_F_LOCAL is set, the preferred_node is ignored and
the policy is interpreted as local allocation. "Local" allocation
policy can be viewed as a Preferred policy that starts at the node
containing the cpu where the allocation takes place.
It is possible for the user to specify that local allocation is
always preferred by passing an empty nodemask with this mode.