[-mm] Add an owner to the mm_struct (v6) - Kernel

This is a discussion on [-mm] Add an owner to the mm_struct (v6) - Kernel ; Changelog v5 ------------ Remove the hooks for .owner from init_task.h and move it to init/main.c Changelog v4 ------------ 1. Release rcu_read_lock() after acquiring task_lock(). Also get a reference to the task_struct 2. Change cgroup mm_owner_changed callback to callback only if ...

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Thread: [-mm] Add an owner to the mm_struct (v6)

  1. [-mm] Add an owner to the mm_struct (v6)



    Changelog v5
    ------------
    Remove the hooks for .owner from init_task.h and move it to init/main.c

    Changelog v4
    ------------
    1. Release rcu_read_lock() after acquiring task_lock(). Also get a reference
    to the task_struct
    2. Change cgroup mm_owner_changed callback to callback only if the
    cgroup of old and new task is different and to pass the old and new
    cgroups instead of task pointers
    3. Port the patch to 2.6.25-rc8-mm1

    Changelog v3
    ------------

    1. Add mm->owner change callbacks using cgroups

    This patch removes the mem_cgroup member from mm_struct and instead adds
    an owner. This approach was suggested by Paul Menage. The advantage of
    this approach is that, once the mm->owner is known, using the subsystem
    id, the cgroup can be determined. It also allows several control groups
    that are virtually grouped by mm_struct, to exist independent of the memory
    controller i.e., without adding mem_cgroup's for each controller,
    to mm_struct.

    A new config option CONFIG_MM_OWNER is added and the memory resource
    controller selects this config option.

    This patch also adds cgroup callbacks to notify subsystems when mm->owner
    changes. The mm_cgroup_changed callback is called with the task_lock()
    of the new task held and is called just prior to changing the mm->owner.

    I am indebted to Paul Menage for the several reviews of this patchset
    and helping me make it lighter and simpler.

    This patch was tested on a powerpc box, it was compiled with both the
    MM_OWNER config turned on and off.

    Signed-off-by: Balbir Singh
    ---

    fs/exec.c | 1
    include/linux/cgroup.h | 15 ++++++++
    include/linux/init_task.h | 1
    include/linux/memcontrol.h | 16 +--------
    include/linux/mm_types.h | 5 +-
    include/linux/sched.h | 13 +++++++
    init/Kconfig | 15 ++++++++
    init/main.c | 1
    kernel/cgroup.c | 30 +++++++++++++++++
    kernel/exit.c | 77 +++++++++++++++++++++++++++++++++++++++++++++
    kernel/fork.c | 11 ++++--
    mm/memcontrol.c | 21 +-----------
    12 files changed, 169 insertions(+), 37 deletions(-)

    diff -puN fs/exec.c~memory-controller-add-mm-owner fs/exec.c
    --- linux-2.6.25-rc8/fs/exec.c~memory-controller-add-mm-owner 2008-04-03 10:08:23.000000000 +0530
    +++ linux-2.6.25-rc8-balbir/fs/exec.c 2008-04-03 10:08:23.000000000 +0530
    @@ -735,6 +735,7 @@ static int exec_mmap(struct mm_struct *m
    tsk->active_mm = mm;
    activate_mm(active_mm, mm);
    task_unlock(tsk);
    + mm_update_next_owner(mm);
    arch_pick_mmap_layout(mm);
    if (old_mm) {
    up_read(&old_mm->mmap_sem);
    diff -puN include/linux/cgroup.h~memory-controller-add-mm-owner include/linux/cgroup.h
    --- linux-2.6.25-rc8/include/linux/cgroup.h~memory-controller-add-mm-owner 2008-04-03 10:08:23.000000000 +0530
    +++ linux-2.6.25-rc8-balbir/include/linux/cgroup.h 2008-04-03 10:33:25.000000000 +0530
    @@ -300,6 +300,12 @@ struct cgroup_subsys {
    struct cgroup *cgrp);
    void (*post_clone)(struct cgroup_subsys *ss, struct cgroup *cgrp);
    void (*bind)(struct cgroup_subsys *ss, struct cgroup *root);
    + /*
    + * This routine is called with the task_lock of mm->owner held
    + */
    + void (*mm_owner_changed)(struct cgroup_subsys *ss,
    + struct cgroup *old,
    + struct cgroup *new);
    int subsys_id;
    int active;
    int disabled;
    @@ -385,4 +391,13 @@ static inline int cgroupstats_build(stru

    #endif /* !CONFIG_CGROUPS */

    +#ifdef CONFIG_MM_OWNER
    +extern void
    +cgroup_mm_owner_callbacks(struct task_struct *old, struct task_struct *new);
    +#else /* !CONFIG_MM_OWNER */
    +static inline void
    +cgroup_mm_owner_callbacks(struct task_struct *old, struct task_struct *new)
    +{
    +}
    +#endif /* CONFIG_MM_OWNER */
    #endif /* _LINUX_CGROUP_H */
    diff -puN include/linux/init_task.h~memory-controller-add-mm-owner include/linux/init_task.h
    --- linux-2.6.25-rc8/include/linux/init_task.h~memory-controller-add-mm-owner 2008-04-03 10:08:23.000000000 +0530
    +++ linux-2.6.25-rc8-balbir/include/linux/init_task.h 2008-04-03 12:14:01.000000000 +0530
    @@ -199,7 +199,6 @@ extern struct group_info init_groups;
    INIT_LOCKDEP \
    }

    -
    #define INIT_CPU_TIMERS(cpu_timers) \
    { \
    LIST_HEAD_INIT(cpu_timers[0]), \
    diff -puN include/linux/memcontrol.h~memory-controller-add-mm-owner include/linux/memcontrol.h
    --- linux-2.6.25-rc8/include/linux/memcontrol.h~memory-controller-add-mm-owner 2008-04-03 10:08:23.000000000 +0530
    +++ linux-2.6.25-rc8-balbir/include/linux/memcontrol.h 2008-04-03 12:43:47.000000000 +0530
    @@ -27,9 +27,6 @@ struct mm_struct;

    #ifdef CONFIG_CGROUP_MEM_RES_CTLR

    -extern void mm_init_cgroup(struct mm_struct *mm, struct task_struct *p);
    -extern void mm_free_cgroup(struct mm_struct *mm);
    -
    #define page_reset_bad_cgroup(page) ((page)->page_cgroup = 0)

    extern struct page_cgroup *page_get_page_cgroup(struct page *page);
    @@ -48,8 +45,10 @@ extern unsigned long mem_cgroup_isolate_
    extern void mem_cgroup_out_of_memory(struct mem_cgroup *mem, gfp_t gfp_mask);
    int task_in_mem_cgroup(struct task_struct *task, const struct mem_cgroup *mem);

    +extern struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p);
    +
    #define mm_match_cgroup(mm, cgroup) \
    - ((cgroup) == rcu_dereference((mm)->mem_cgroup))
    + ((cgroup) == mem_cgroup_from_task((mm)->owner))

    extern int mem_cgroup_prepare_migration(struct page *page);
    extern void mem_cgroup_end_migration(struct page *page);
    @@ -73,15 +72,6 @@ extern long mem_cgroup_calc_reclaim_inac
    struct zone *zone, int priority);

    #else /* CONFIG_CGROUP_MEM_RES_CTLR */
    -static inline void mm_init_cgroup(struct mm_struct *mm,
    - struct task_struct *p)
    -{
    -}
    -
    -static inline void mm_free_cgroup(struct mm_struct *mm)
    -{
    -}
    -
    static inline void page_reset_bad_cgroup(struct page *page)
    {
    }
    diff -puN include/linux/mm_types.h~memory-controller-add-mm-owner include/linux/mm_types.h
    --- linux-2.6.25-rc8/include/linux/mm_types.h~memory-controller-add-mm-owner 2008-04-03 10:08:23.000000000 +0530
    +++ linux-2.6.25-rc8-balbir/include/linux/mm_types.h 2008-04-03 10:08:23.000000000 +0530
    @@ -230,8 +230,9 @@ struct mm_struct {
    /* aio bits */
    rwlock_t ioctx_list_lock; /* aio lock */
    struct kioctx *ioctx_list;
    -#ifdef CONFIG_CGROUP_MEM_RES_CTLR
    - struct mem_cgroup *mem_cgroup;
    +#ifdef CONFIG_MM_OWNER
    + struct task_struct *owner; /* The thread group leader that */
    + /* owns the mm_struct. */
    #endif

    #ifdef CONFIG_PROC_FS
    diff -puN include/linux/sched.h~memory-controller-add-mm-owner include/linux/sched.h
    --- linux-2.6.25-rc8/include/linux/sched.h~memory-controller-add-mm-owner 2008-04-03 10:08:23.000000000 +0530
    +++ linux-2.6.25-rc8-balbir/include/linux/sched.h 2008-04-03 12:52:15.000000000 +0530
    @@ -2144,6 +2144,19 @@ static inline void migration_init(void)

    #define TASK_STATE_TO_CHAR_STR "RSDTtZX"

    +#ifdef CONFIG_MM_OWNER
    +extern void mm_update_next_owner(struct mm_struct *mm);
    +extern void mm_init_owner(struct mm_struct *mm, struct task_struct *p);
    +#else
    +static inline void mm_update_next_owner(struct mm_struct *mm)
    +{
    +}
    +
    +static inline void mm_init_owner(struct mm_struct *mm, struct task_struct *p)
    +{
    +}
    +#endif /* CONFIG_MM_OWNER */
    +
    #endif /* __KERNEL__ */

    #endif
    diff -puN init/Kconfig~memory-controller-add-mm-owner init/Kconfig
    --- linux-2.6.25-rc8/init/Kconfig~memory-controller-add-mm-owner 2008-04-03 10:08:23.000000000 +0530
    +++ linux-2.6.25-rc8-balbir/init/Kconfig 2008-04-03 10:08:23.000000000 +0530
    @@ -371,9 +371,21 @@ config RESOURCE_COUNTERS
    infrastructure that works with cgroups
    depends on CGROUPS

    +config MM_OWNER
    + bool "Enable ownership of mm structure"
    + help
    + This option enables mm_struct's to have an owner. The advantage
    + of this approach is that it allows for several independent memory
    + based cgorup controllers to co-exist independently without too
    + much space overhead
    +
    + This feature adds fork/exit overhead. So enable this only if
    + you need resource controllers
    +
    config CGROUP_MEM_RES_CTLR
    bool "Memory Resource Controller for Control Groups"
    depends on CGROUPS && RESOURCE_COUNTERS
    + select MM_OWNER
    help
    Provides a memory resource controller that manages both page cache and
    RSS memory.
    @@ -386,6 +398,9 @@ config CGROUP_MEM_RES_CTLR
    Only enable when you're ok with these trade offs and really
    sure you need the memory resource controller.

    + This config option also selects MM_OWNER config option, which
    + could in turn add some fork/exit overhead.
    +
    config SYSFS_DEPRECATED
    bool

    diff -puN kernel/cgroup.c~memory-controller-add-mm-owner kernel/cgroup.c
    --- linux-2.6.25-rc8/kernel/cgroup.c~memory-controller-add-mm-owner 2008-04-03 10:08:23.000000000 +0530
    +++ linux-2.6.25-rc8-balbir/kernel/cgroup.c 2008-04-03 10:34:15.000000000 +0530
    @@ -118,6 +118,7 @@ static int root_count;
    * be called.
    */
    static int need_forkexit_callback;
    +static int need_mm_owner_callback;

    /* convenient tests for these bits */
    inline int cgroup_is_removed(const struct cgroup *cgrp)
    @@ -2485,6 +2486,7 @@ static void __init cgroup_init_subsys(st
    }

    need_forkexit_callback |= ss->fork || ss->exit;
    + need_mm_owner_callback |= !!ss->mm_owner_changed;

    ss->active = 1;
    }
    @@ -2721,6 +2723,34 @@ void cgroup_fork_callbacks(struct task_s
    }
    }

    +#ifdef CONFIG_MM_OWNER
    +/**
    + * cgroup_mm_owner_callbacks - run callbacks when the mm->owner changes
    + * @p: the new owner
    + *
    + * Called on every change to mm->owner. mm_init_owner() does not
    + * invoke this routine, since it assigns the mm->owner the first time
    + * and does not change it.
    + */
    +void cgroup_mm_owner_callbacks(struct task_struct *old, struct task_struct *new)
    +{
    + struct cgroup *oldcgrp, *newcgrp;
    +
    + if (need_mm_owner_callback) {
    + int i;
    + for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
    + struct cgroup_subsys *ss = subsys[i];
    + oldcgrp = task_cgroup(old, ss->subsys_id);
    + newcgrp = task_cgroup(new, ss->subsys_id);
    + if (oldcgrp == newcgrp)
    + continue;
    + if (ss->mm_owner_changed)
    + ss->mm_owner_changed(ss, oldcgrp, newcgrp);
    + }
    + }
    +}
    +#endif /* CONFIG_MM_OWNER */
    +
    /**
    * cgroup_post_fork - called on a new task after adding it to the task list
    * @child: the task in question
    diff -puN kernel/exit.c~memory-controller-add-mm-owner kernel/exit.c
    --- linux-2.6.25-rc8/kernel/exit.c~memory-controller-add-mm-owner 2008-04-03 10:08:23.000000000 +0530
    +++ linux-2.6.25-rc8-balbir/kernel/exit.c 2008-04-03 10:27:21.000000000 +0530
    @@ -577,6 +577,82 @@ void exit_fs(struct task_struct *tsk)

    EXPORT_SYMBOL_GPL(exit_fs);

    +#ifdef CONFIG_MM_OWNER
    +/*
    + * Task p is exiting and it owned p, so lets find a new owner for it
    + */
    +static inline int
    +mm_need_new_owner(struct mm_struct *mm, struct task_struct *p)
    +{
    + int ret;
    +
    + ret = (mm && (atomic_read(&mm->mm_users) > 1) && (mm->owner == p) &&
    + !delay_group_leader(p));
    + return ret;
    +}
    +
    +void mm_update_next_owner(struct mm_struct *mm)
    +{
    + struct task_struct *c, *g, *p = current;
    +
    +retry:
    + if (!mm_need_new_owner(mm, p))
    + return;
    +
    + rcu_read_lock();
    + /*
    + * Search in the children
    + */
    + list_for_each_entry(c, &p->children, sibling) {
    + if (c->mm == mm)
    + goto assign_new_owner;
    + }
    +
    + /*
    + * Search in the siblings
    + */
    + list_for_each_entry(c, &p->parent->children, sibling) {
    + if (c->mm == mm)
    + goto assign_new_owner;
    + }
    +
    + /*
    + * Search through everything else. We should not get
    + * here often
    + */
    + do_each_thread(g, c) {
    + if (c->mm == mm)
    + goto assign_new_owner;
    + } while_each_thread(g, c);
    +
    + rcu_read_unlock();
    + return;
    +
    +assign_new_owner:
    + BUG_ON(c == p);
    + get_task_struct(c);
    + /*
    + * The task_lock protects c->mm from changing.
    + * We always want mm->owner->mm == mm
    + */
    + task_lock(c);
    + /*
    + * Delay rcu_read_unlock() till we have the task_lock()
    + * to ensure that c does not slip away underneath us
    + */
    + rcu_read_unlock();
    + if (c->mm != mm) {
    + task_unlock(c);
    + put_task_struct(c);
    + goto retry;
    + }
    + cgroup_mm_owner_callbacks(mm->owner, c);
    + mm->owner = c;
    + task_unlock(c);
    + put_task_struct(c);
    +}
    +#endif /* CONFIG_MM_OWNER */
    +
    /*
    * Turn us into a lazy TLB process if we
    * aren't already..
    @@ -616,6 +692,7 @@ static void exit_mm(struct task_struct *
    /* We don't want this task to be frozen prematurely */
    clear_freeze_flag(tsk);
    task_unlock(tsk);
    + mm_update_next_owner(mm);
    mmput(mm);
    }

    diff -puN kernel/fork.c~memory-controller-add-mm-owner kernel/fork.c
    --- linux-2.6.25-rc8/kernel/fork.c~memory-controller-add-mm-owner 2008-04-03 10:08:23.000000000 +0530
    +++ linux-2.6.25-rc8-balbir/kernel/fork.c 2008-04-03 12:23:57.000000000 +0530
    @@ -358,14 +358,13 @@ static struct mm_struct * mm_init(struct
    mm->ioctx_list = NULL;
    mm->free_area_cache = TASK_UNMAPPED_BASE;
    mm->cached_hole_size = ~0UL;
    - mm_init_cgroup(mm, p);
    + mm_init_owner(mm, p);

    if (likely(!mm_alloc_pgd(mm))) {
    mm->def_flags = 0;
    return mm;
    }

    - mm_free_cgroup(mm);
    free_mm(mm);
    return NULL;
    }
    @@ -416,7 +415,6 @@ void mmput(struct mm_struct *mm)
    spin_unlock(&mmlist_lock);
    }
    put_swap_token(mm);
    - mm_free_cgroup(mm);
    mmdrop(mm);
    }
    }
    @@ -996,6 +994,13 @@ static void rt_mutex_init_task(struct ta
    #endif
    }

    +#ifdef CONFIG_MM_OWNER
    +void mm_init_owner(struct mm_struct *mm, struct task_struct *p)
    +{
    + mm->owner = p;
    +}
    +#endif /* CONFIG_MM_OWNER */
    +
    /*
    * This creates a new process as a copy of the old one,
    * but does not actually start it yet.
    diff -puN mm/memcontrol.c~memory-controller-add-mm-owner mm/memcontrol.c
    --- linux-2.6.25-rc8/mm/memcontrol.c~memory-controller-add-mm-owner 2008-04-03 10:08:23.000000000 +0530
    +++ linux-2.6.25-rc8-balbir/mm/memcontrol.c 2008-04-03 10:08:23.000000000 +0530
    @@ -238,26 +238,12 @@ static struct mem_cgroup *mem_cgroup_fro
    css);
    }

    -static struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p)
    +struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p)
    {
    return container_of(task_subsys_state(p, mem_cgroup_subsys_id),
    struct mem_cgroup, css);
    }

    -void mm_init_cgroup(struct mm_struct *mm, struct task_struct *p)
    -{
    - struct mem_cgroup *mem;
    -
    - mem = mem_cgroup_from_task(p);
    - css_get(&mem->css);
    - mm->mem_cgroup = mem;
    -}
    -
    -void mm_free_cgroup(struct mm_struct *mm)
    -{
    - css_put(&mm->mem_cgroup->css);
    -}
    -
    static inline int page_cgroup_locked(struct page *page)
    {
    return bit_spin_is_locked(PAGE_CGROUP_LOCK_BIT, &page->page_cgroup);
    @@ -478,6 +464,7 @@ unsigned long mem_cgroup_isolate_pages(u
    int zid = zone_idx(z);
    struct mem_cgroup_per_zone *mz;

    + BUG_ON(!mem_cont);
    mz = mem_cgroup_zoneinfo(mem_cont, nid, zid);
    if (active)
    src = &mz->active_list;
    @@ -576,7 +563,7 @@ retry:
    mm = &init_mm;

    rcu_read_lock();
    - mem = rcu_dereference(mm->mem_cgroup);
    + mem = mem_cgroup_from_task(rcu_dereference(mm->owner));
    /*
    * For every charge from the cgroup, increment reference count
    */
    @@ -1006,7 +993,6 @@ mem_cgroup_create(struct cgroup_subsys *

    if (unlikely((cont->parent) == NULL)) {
    mem = &init_mem_cgroup;
    - init_mm.mem_cgroup = mem;
    page_cgroup_cache = KMEM_CACHE(page_cgroup, SLAB_PANIC);
    } else
    mem = kzalloc(sizeof(struct mem_cgroup), GFP_KERNEL);
    @@ -1088,7 +1074,6 @@ static void mem_cgroup_move_task(struct
    goto out;

    css_get(&mem->css);
    - rcu_assign_pointer(mm->mem_cgroup, mem);
    css_put(&old_mem->css);

    out:
    diff -puN init/main.c~memory-controller-add-mm-owner init/main.c
    --- linux-2.6.25-rc8/init/main.c~memory-controller-add-mm-owner 2008-04-03 12:24:02.000000000 +0530
    +++ linux-2.6.25-rc8-balbir/init/main.c 2008-04-03 12:25:25.000000000 +0530
    @@ -537,6 +537,7 @@ asmlinkage void __init start_kernel(void
    printk(KERN_NOTICE);
    printk(linux_banner);
    setup_arch(&command_line);
    + mm_init_owner(&init_mm, &init_task);
    setup_command_line(command_line);
    unwind_setup();
    setup_per_cpu_areas();
    _

    --
    Warm Regards,
    Balbir Singh
    Linux Technology Center
    IBM, ISTL
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  2. Re: [-mm] Add an owner to the mm_struct (v6)

    On Thu, Apr 3, 2008 at 12:30 AM, Balbir Singh wrote:
    > + This option enables mm_struct's to have an owner. The advantage
    > + of this approach is that it allows for several independent memory
    > + based cgorup controllers to co-exist independently without too


    cgorup -> cgroup

    > + if (need_mm_owner_callback) {
    > + int i;
    > + for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
    > + struct cgroup_subsys *ss = subsys[i];
    > + oldcgrp = task_cgroup(old, ss->subsys_id);
    > + newcgrp = task_cgroup(new, ss->subsys_id);
    > + if (oldcgrp == newcgrp)
    > + continue;
    > + if (ss->mm_owner_changed)
    > + ss->mm_owner_changed(ss, oldcgrp, newcgrp);


    Even better, maybe just pass in the relevant cgroup_subsys_state
    objects here, rather than the cgroup objects?

    >
    > css_get(&mem->css);
    > - rcu_assign_pointer(mm->mem_cgroup, mem);
    > css_put(&old_mem->css);


    These get/put calls are now unwanted?

    Could you also add comments in mm_need_new_owner(), in particular the
    reason for checking for delay_group_leader() ?

    Paul
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  3. Re: [-mm] Add an owner to the mm_struct (v6)

    Paul Menage wrote:
    > On Thu, Apr 3, 2008 at 12:30 AM, Balbir Singh wrote:
    >> + This option enables mm_struct's to have an owner. The advantage
    >> + of this approach is that it allows for several independent memory
    >> + based cgorup controllers to co-exist independently without too

    >
    > cgorup -> cgroup
    >


    yes, typo

    >> + if (need_mm_owner_callback) {
    >> + int i;
    >> + for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
    >> + struct cgroup_subsys *ss = subsys[i];
    >> + oldcgrp = task_cgroup(old, ss->subsys_id);
    >> + newcgrp = task_cgroup(new, ss->subsys_id);
    >> + if (oldcgrp == newcgrp)
    >> + continue;
    >> + if (ss->mm_owner_changed)
    >> + ss->mm_owner_changed(ss, oldcgrp, newcgrp);

    >
    > Even better, maybe just pass in the relevant cgroup_subsys_state
    > objects here, rather than the cgroup objects?
    >


    Is that better than passing the cgroups? All the callbacks I see usually pass
    either task_struct or cgroup. Won't it be better, consistent use of API to pass
    either of those?

    >> css_get(&mem->css);
    >> - rcu_assign_pointer(mm->mem_cgroup, mem);
    >> css_put(&old_mem->css);

    >
    > These get/put calls are now unwanted?
    >


    Yes, will remove them

    > Could you also add comments in mm_need_new_owner(), in particular the
    > reason for checking for delay_group_leader() ?


    Yep, will do

    --
    Warm Regards,
    Balbir Singh
    Linux Technology Center
    IBM, ISTL
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  4. Re: [-mm] Add an owner to the mm_struct (v6)

    On Thu, Apr 3, 2008 at 10:15 AM, Balbir Singh wrote:
    > > Even better, maybe just pass in the relevant cgroup_subsys_state
    > > objects here, rather than the cgroup objects?
    > >

    >
    > Is that better than passing the cgroups? All the callbacks I see usually pass
    > either task_struct or cgroup. Won't it be better, consistent use of API to pass
    > either of those?


    I have a long term plan to try to divorce the subsystems from having
    to worry too much about actual control groups where possible.

    But I guess that for consistency with the current API, passing in the
    cgroup is OK.

    Paul
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