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    Subject[PATCH incremental] cpusets: initialize spread rotor lazily
    On Fri 15-04-11 16:42:13, David Rientjes wrote:
    > On Fri, 15 Apr 2011, Michal Hocko wrote:
    >
    > > You are right. I was thinking about lazy approach and initialize those
    > > values when they are used for the first time. What about the patch
    > > below?
    > >
    > > Change from v1:
    > > - initialize cpuset_{mem,slab}_spread_rotor lazily
    > >
    >
    > The difference between this v2 patch and what is already in the -mm tree
    > (http://userweb.kernel.org/~akpm/mmotm/broken-out/cpusets-randomize-node-rotor-used-in-cpuset_mem_spread_node.patch)
    > is the lazy initialization by adding cpuset_{mem,slab}_spread_node()?

    Yes.

    > It'd probably be better to just make an incremental patch on top of
    > mmotm-2011-04-14-15-08 with a new changelog and then propose with with
    > your list of reviewed-by lines.

    Sure, no problems. Maybe it will be easier for Andrew as well.

    >
    > Andrew could easily drop the earlier version and merge this v2, but I'm
    > asking for selfish reasons:

    Just out of curiosity. What is the reason? Don't want to wait for new mmotm?

    > please use NUMA_NO_NODE instead of -1.

    Good idea. I have updated the patch.

    Changes from v2:
    - use NUMA_NO_NODE rather than hardcoded -1
    - make the patch incremental to the original one because that one is in
    -mm tree already.
    Changes from v1:
    - initialize cpuset_{mem,slab}_spread_rotor lazily}

    [Here is the follow-up patch based on top of
    http://userweb.kernel.org/~akpm/mmotm/broken-out/cpusets-randomize-node-rotor-used-in-cpuset_mem_spread_node.patch]
    ---
    From: Michal Hocko <mhocko@suse.cz>
    Subject: cpusets: initialize spread mem/slab rotor lazily

    Kosaki Motohiro raised a concern that copy_process is hot path and we do
    not want to initialize cpuset_{mem,slab}_spread_rotor if they are not
    used most of the time.

    I think that we should rather intialize it lazily when rotors are used
    for the first time.
    This will also catch the case when we set up spread mem/slab later.

    Also do not use -1 for unitialized nodes and rather use NUMA_NO_NODE
    instead.

    Signed-off-by: Michal Hocko <mhocko@suse.cz>
    Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
    ---
    cpuset.c | 8 ++++++++
    fork.c | 4 ++--
    2 files changed, 10 insertions(+), 2 deletions(-)
    Index: linus_tree/kernel/cpuset.c
    ===================================================================
    --- linus_tree.orig/kernel/cpuset.c 2011-04-18 10:33:15.000000000 +0200
    +++ linus_tree/kernel/cpuset.c 2011-04-18 10:33:56.000000000 +0200
    @@ -2460,11 +2460,19 @@ static int cpuset_spread_node(int *rotor

    int cpuset_mem_spread_node(void)
    {
    + if (current->cpuset_mem_spread_rotor == NUMA_NO_NODE)
    + current->cpuset_mem_spread_rotor =
    + node_random(&current->mems_allowed);
    +
    return cpuset_spread_node(&current->cpuset_mem_spread_rotor);
    }

    int cpuset_slab_spread_node(void)
    {
    + if (current->cpuset_slab_spread_rotor == NUMA_NO_NODE)
    + current->cpuset_slab_spread_rotor
    + = node_random(&current->mems_allowed);
    +
    return cpuset_spread_node(&current->cpuset_slab_spread_rotor);
    }

    Index: linus_tree/kernel/fork.c
    ===================================================================
    --- linus_tree.orig/kernel/fork.c 2011-04-18 10:33:15.000000000 +0200
    +++ linus_tree/kernel/fork.c 2011-04-18 10:33:56.000000000 +0200
    @@ -1126,8 +1126,8 @@ static struct task_struct *copy_process(
    mpol_fix_fork_child_flag(p);
    #endif
    #ifdef CONFIG_CPUSETS
    - p->cpuset_mem_spread_rotor = node_random(&p->mems_allowed);
    - p->cpuset_slab_spread_rotor = node_random(&p->mems_allowed);
    + p->cpuset_mem_spread_rotor = NUMA_NO_NODE;
    + p->cpuset_slab_spread_rotor = NUMA_NO_NODE;
    #endif
    #ifdef CONFIG_TRACE_IRQFLAGS
    p->irq_events = 0;
    --
    Michal Hocko
    SUSE Labs
    SUSE LINUX s.r.o.
    Lihovarska 1060/12
    190 00 Praha 9
    Czech Republic

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