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    Subject[PATCH v2] cpusets: randomize node rotor used in cpuset_mem_spread_node()
    [I just realized that I forgot to CC mm mailing list]

    On Fri 15-04-11 16:18:45, KOSAKI Motohiro wrote:
    > Oops.
    > I should have look into !mempolicy part too.
    > I'm sorry.
    >
    [...]
    > Michal, I think this should be
    >
    > #ifdef CONFIG_CPUSETS
    > if (cpuset_do_page_mem_spread())
    > p->cpuset_mem_spread_rotor = node_random(&p->mems_allowed);
    > if (cpuset_do_slab_mem_spread())
    > p->cpuset_slab_spread_rotor = node_random(&p->mems_allowed);
    > #endif
    >
    > because 99.999% people don't use cpuset's spread mem/slab feature and
    > get_random_int() isn't zero cost.
    >
    > What do you think?

    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

    ---
    From 46da525789a41cb10096aa09c5bc0e7dcc3ce6db Mon Sep 17 00:00:00 2001
    From: Michal Hocko <mhocko@suse.cz>
    Date: Wed, 13 Apr 2011 16:29:36 +0200
    Subject: [PATCH] cpusets: randomize node rotor used in cpuset_mem_spread_node()

    [This patch has already been accepted as 0ac0c0d but later reverted
    (35926ff) because it itroduced arch specific __node_random which was
    defined only for x86 code so it broke other archs.
    This is a followup without any arch specific code. Other than that there
    are no functional changes.]

    Some workloads that create a large number of small files tend to assign
    too many pages to node 0 (multi-node systems). Part of the reason is that
    the rotor (in cpuset_mem_spread_node()) used to assign nodes starts at
    node 0 for newly created tasks.

    This patch changes the rotor to be initialized to a random node number of
    the cpuset. We are initializating it lazily in cpuset_mem_spread_node
    resp. cpuset_slab_spread_node.

    [akpm@linux-foundation.org: fix layout]
    [Lee.Schermerhorn@hp.com: Define stub numa_random() for !NUMA configuration]
    [mhocko@suse.cz: Make it arch independent + lazy initialization]
    Signed-off-by: Jack Steiner <steiner@sgi.com>
    Signed-off-by: Lee Schermerhorn <lee.schermerhorn@hp.com>
    Signed-off-by: Michal Hocko <mhocko@suse.cz>
    Cc: Christoph Lameter <cl@linux-foundation.org>
    Cc: Pekka Enberg <penberg@cs.helsinki.fi>
    Cc: Paul Menage <menage@google.com>
    Cc: Jack Steiner <steiner@sgi.com>
    Cc: Robin Holt <holt@sgi.com>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    ---
    include/linux/bitmap.h | 1 +
    include/linux/nodemask.h | 7 +++++++
    kernel/cpuset.c | 8 ++++++++
    kernel/fork.c | 5 +++++
    lib/bitmap.c | 2 +-
    mm/mempolicy.c | 16 ++++++++++++++++
    6 files changed, 38 insertions(+), 1 deletions(-)

    diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h
    index daf8c48..6fb2720 100644
    --- a/include/linux/bitmap.h
    +++ b/include/linux/bitmap.h
    @@ -141,6 +141,7 @@ extern int bitmap_find_free_region(unsigned long *bitmap, int bits, int order);
    extern void bitmap_release_region(unsigned long *bitmap, int pos, int order);
    extern int bitmap_allocate_region(unsigned long *bitmap, int pos, int order);
    extern void bitmap_copy_le(void *dst, const unsigned long *src, int nbits);
    +extern int bitmap_ord_to_pos(const unsigned long *bitmap, int n, int bits);

    #define BITMAP_LAST_WORD_MASK(nbits) \
    ( \
    diff --git a/include/linux/nodemask.h b/include/linux/nodemask.h
    index dba35e4..66ccda9 100644
    --- a/include/linux/nodemask.h
    +++ b/include/linux/nodemask.h
    @@ -66,6 +66,8 @@
    * int num_online_nodes() Number of online Nodes
    * int num_possible_nodes() Number of all possible Nodes
    *
    + * int node_random(mask) Random node with set bit in mask
    + *
    * int node_online(node) Is some node online?
    * int node_possible(node) Is some node possible?
    *
    @@ -430,6 +432,9 @@ static inline void node_set_offline(int nid)
    node_clear_state(nid, N_ONLINE);
    nr_online_nodes = num_node_state(N_ONLINE);
    }
    +
    +extern int node_random(const nodemask_t *maskp);
    +
    #else

    static inline int node_state(int node, enum node_states state)
    @@ -460,6 +465,8 @@ static inline int num_node_state(enum node_states state)

    #define node_set_online(node) node_set_state((node), N_ONLINE)
    #define node_set_offline(node) node_clear_state((node), N_ONLINE)
    +
    +static inline int node_random(const nodemask_t *mask) { return 0; }
    #endif

    #define node_online_map node_states[N_ONLINE]
    diff --git a/kernel/cpuset.c b/kernel/cpuset.c
    index 33eee16..5376478 100644
    --- a/kernel/cpuset.c
    +++ b/kernel/cpuset.c
    @@ -2465,11 +2465,19 @@ static int cpuset_spread_node(int *rotor)

    int cpuset_mem_spread_node(void)
    {
    + if (current->cpuset_mem_spread_rotor == -1)
    + 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 == -1)
    + current->cpuset_slab_spread_rotor
    + = node_random(&current->mems_allowed);
    +
    return cpuset_spread_node(&current->cpuset_slab_spread_rotor);
    }

    diff --git a/kernel/fork.c b/kernel/fork.c
    index e7548de..0883cff 100644
    --- a/kernel/fork.c
    +++ b/kernel/fork.c
    @@ -1119,6 +1119,11 @@ static struct task_struct *copy_process(unsigned long clone_flags,
    }
    mpol_fix_fork_child_flag(p);
    #endif
    +#ifdef CONFIG_CPUSETS
    + /* Will be initialized lazily when first used */
    + p->cpuset_mem_spread_rotor = -1;
    + p->cpuset_slab_spread_rotor = -1;
    +#endif
    #ifdef CONFIG_TRACE_IRQFLAGS
    p->irq_events = 0;
    #ifdef __ARCH_WANT_INTERRUPTS_ON_CTXSW
    diff --git a/lib/bitmap.c b/lib/bitmap.c
    index 91e0ccf..a4b5217 100644
    --- a/lib/bitmap.c
    +++ b/lib/bitmap.c
    @@ -671,7 +671,7 @@ static int bitmap_pos_to_ord(const unsigned long *buf, int pos, int bits)
    *
    * The bit positions 0 through @bits are valid positions in @buf.
    */
    -static int bitmap_ord_to_pos(const unsigned long *buf, int ord, int bits)
    +int bitmap_ord_to_pos(const unsigned long *buf, int ord, int bits)
    {
    int pos = 0;

    diff --git a/mm/mempolicy.c b/mm/mempolicy.c
    index 959a8b8..8e57a72 100644
    --- a/mm/mempolicy.c
    +++ b/mm/mempolicy.c
    @@ -93,6 +93,7 @@

    #include <asm/tlbflush.h>
    #include <asm/uaccess.h>
    +#include <linux/random.h>

    #include "internal.h"

    @@ -1649,6 +1650,21 @@ static inline unsigned interleave_nid(struct mempolicy *pol,
    return interleave_nodes(pol);
    }

    +/*
    + * Return the bit number of a random bit set in the nodemask.
    + * (returns -1 if nodemask is empty)
    + */
    +int node_random(const nodemask_t *maskp)
    +{
    + int w, bit = -1;
    +
    + w = nodes_weight(*maskp);
    + if (w)
    + bit = bitmap_ord_to_pos(maskp->bits,
    + get_random_int() % w, MAX_NUMNODES);
    + return bit;
    +}
    +
    #ifdef CONFIG_HUGETLBFS
    /*
    * huge_zonelist(@vma, @addr, @gfp_flags, @mpol)
    --
    1.7.4.1

    --
    Michal Hocko
    SUSE Labs
    SUSE LINUX s.r.o.
    Lihovarska 1060/12
    190 00 Praha 9
    Czech Republic


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