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    Subjectcpusets: randomize node rotor used in cpuset_mem_spread_node()
    Hi,
    I have revisited and fixed the following patch. I am keeping Jack's and
    Lee's s-o-b and all others are CCed because I am not exactly sure who
    worked on the patch originally.
    Can we consider it for re-inclusion?
    ---
    From 4a2cfbdcfeae9d49ae9ff3486150bec2e4c6107e 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.

    [akpm@linux-foundation.org: fix layout]
    [Lee.Schermerhorn@hp.com: Define stub numa_random() for !NUMA configuration]
    [mhocko@suse.cz: Make it arch independent]
    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/fork.c | 4 ++++
    lib/bitmap.c | 2 +-
    mm/mempolicy.c | 16 ++++++++++++++++
    5 files changed, 29 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/fork.c b/kernel/fork.c
    index e7548de..f59c686 100644
    --- a/kernel/fork.c
    +++ b/kernel/fork.c
    @@ -1119,6 +1119,10 @@ static struct task_struct *copy_process(unsigned long clone_flags,
    }
    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);
    +#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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