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authorLee Schermerhorn <lee.schermerhorn@hp.com>2008-04-28 02:13:21 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2008-04-28 08:58:24 -0700
commitfc36b8d3d819047eb4d23ca079fb4d3af20ff076 (patch)
tree65ee215a6bdca1e8d4ac4b57525445d7d1829c1d /Documentation/vm
parent53f2556b6792ed99fde965f5e061749edd455623 (diff)
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mempolicy: use MPOL_F_LOCAL to Indicate Preferred Local Policy
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>
Diffstat (limited to 'Documentation/vm')
-rw-r--r--Documentation/vm/numa_memory_policy.txt11
1 files changed, 5 insertions, 6 deletions
diff --git a/Documentation/vm/numa_memory_policy.txt b/Documentation/vm/numa_memory_policy.txt
index 13cca5a3cf1..bad16d3f6a4 100644
--- a/Documentation/vm/numa_memory_policy.txt
+++ b/Documentation/vm/numa_memory_policy.txt
@@ -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.