Messages in this thread Patch in this message |  | | | Date | Wed, 22 Sep 2004 23:32:45 -0500 (CDT) | | From | Ray Bryant <> | | Subject | [PATCH 2/2] mm: eliminate node 0 bias in MPOL_INTERLEAVE |
This is a new patch in this series (it does not in any way replaced the MPOL_ROUDROBIN patch, which has been dropped).
This patches fixes the following problems with MPOL_INTERLEAVE: In the existing implementation, every time a new process is created and it is using MPOL_INTERLEAVE, the interleave "rotator" (current->il_next) is set to zero. This biases storage allocation toward lower numberd nodes (this effect is more apparent on systems with hundreds of nodes.) This patch fixes this problem by setting il_next to pid % MAX_NUMNODES.
Similarly, in the existing implementation of MPOL_INTERLEAVE, each time a new policy of type MPOL_INTERLEAVE is created, current->il_next is set to the lowest numbered node that is in the policy mask policy->v.nodes. This biass storage allocation toward the lowest numbered node in that mask. This is again fixed by setting il_next to pid % MAX_NUMNODES.
Each of these cases potentially breaks the (assumed) invariant of interleave_nodes(), that is that "bit il_next of the nodemask is set" (because the value of il_next on entry to interleave_nodes() is returned as the node to be used for the allocation, and we calculate the next il_next, before returning.)
Solving this requires adding the small bit of code in interleave_nodes() that checks the invariant and if it is not true, updates the return value to be the next bit in the nodemask that is set.
Signed-off-by: Ray Bryant <raybry@sgi.com>
Index: linux-2.6.9-rc2-mm1/mm/mempolicy.c =================================================================== --- linux-2.6.9-rc2-mm1.orig/mm/mempolicy.c 2004-09-21 16:49:00.000000000 -0700 +++ linux-2.6.9-rc2-mm1/mm/mempolicy.c 2004-09-21 17:44:58.000000000 -0700 @@ -435,7 +435,7 @@ asmlinkage long sys_set_mempolicy(int re default_policy[policy] = new; } if (new && new->policy == MPOL_INTERLEAVE) - current->il_next = find_first_bit(new->v.nodes, MAX_NUMNODES); + current->il_next = current->pid % MAX_NUMNODES; return 0; } @@ -714,6 +714,11 @@ static unsigned interleave_nodes(struct nid = me->il_next; BUG_ON(nid >= MAX_NUMNODES); + if (!test_bit(nid, policy->v.nodes)) { + nid = find_next_bit(policy->v.nodes, MAX_NUMNODES, 1+nid); + if (nid >= MAX_NUMNODES) + nid = find_first_bit(policy->v.nodes, MAX_NUMNODES); + } next = find_next_bit(policy->v.nodes, MAX_NUMNODES, 1+nid); if (next >= MAX_NUMNODES) next = find_first_bit(policy->v.nodes, MAX_NUMNODES); Index: linux-2.6.9-rc2-mm1/kernel/fork.c =================================================================== --- linux-2.6.9-rc2-mm1.orig/kernel/fork.c 2004-09-21 16:24:49.000000000 -0700 +++ linux-2.6.9-rc2-mm1/kernel/fork.c 2004-09-21 17:41:12.000000000 -0700 @@ -873,6 +873,8 @@ static task_t *copy_process(unsigned lon goto bad_fork_cleanup; } } + /* randomize placement of first page across nodes */ + p->il_next = p->pid % MAX_NUMNODES; #endif p->tgid = p->pid; - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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