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Date: Tue, 20 Mar 2007 15:12:24 -0700
From: Randy Dunlap <randy.dunlap@...cle.com>
To: cpw@....com (Cliff Wickman)
Cc: linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] hotplug cpu: move tasks in empty cpusets to parent
On Tue, 20 Mar 2007 13:34:01 -0600 Cliff Wickman wrote:
>
> From: Cliff Wickman <cpw@....com>
>
> This patch corrects a situation that occurs when one disables all the cpus
> in a cpuset.
>
> At that point, any tasks in that cpuset are incorrectly moved (as I recall,
> they were move to a sibling cpuset).
> Such tasks should be move the parent of their current cpuset. Or if the
> parent cpuset has no cpus, to its parent, etc.
>
> And the empty cpuset should be removed (if it is flagged notify_on_release).
>
> This patch contains the added complexity of taking care not to do memory
> allocation while holding the cpusets callback_mutex. And it makes use of the
> "cpuset_release_agent" to do the cpuset removals.
>
> It might be simpler to use a separate thread or workqueue. But such code
> has not yet been written.
>
> Diffed against 2.6.20-rc6
>
> Signed-off-by: Cliff Wickman <cpw@....com>
>
> ---
> kernel/cpuset.c | 200 ++++++++++++++++++++++++++++++++++++++++++++++++++------
> 1 file changed, 180 insertions(+), 20 deletions(-)
>
> Index: morton.070205/kernel/cpuset.c
> ===================================================================
> --- morton.070205.orig/kernel/cpuset.c
> +++ morton.070205/kernel/cpuset.c
> @@ -2070,20 +2097,100 @@ out:
> *
> * Call with both manage_mutex and callback_mutex held.
> *
> + * Takes tasklist_lock, and task_lock() for cpuset members that are
> + * moved to another cpuset.
> + *
> * Recursive, on depth of cpuset subtree.
> */
>
> -static void guarantee_online_cpus_mems_in_subtree(const struct cpuset *cur)
> +static void remove_tasks_in_empty_cpusets_in_subtree(const struct cpuset *cur, struct list_head *empty_list, struct path_list_element **ple_array, int *ple_availp, int ple_count)
That line is way too long. Source lines should fit in 80 columns unless
they contain (maybe) a printk string that would be ugly if split (e.g.).
This one should be like so (or some other readable variant):
static void remove_tasks_in_empty_cpusets_in_subtree(
const struct cpuset *cur,
struct list_head *empty_list,
struct path_list_element **ple_array,
int *ple_availp, int ple_count)
> +{
> + int npids, ple_used=0;
> + struct cpuset *c, *parent;
> + struct path_list_element *ple;
> +
> + /* If a cpuset's mems or cpus are empty, move its tasks to its parent */
> + list_for_each_entry(c, &cur->children, sibling) {
> + remove_tasks_in_empty_cpusets_in_subtree(c, empty_list,
> + ple_array, ple_availp, ple_count);
> + /*
> + * If it has no online cpus or no online mems, move its tasks
> + * to its next-highest non-empty parent and remove it.
> + * Remove it even if it has children, as its children are a
> + * subset of cpus and nodes, so they are empty too.
> + * The removal is conditional on whether it is
> + * notify-on-release.
> + */
> + if (cpus_empty(c->cpus_allowed) ||
> + nodes_empty(c->mems_allowed)) {
> + char *path = NULL;
> + /*
> + * Find its next-highest non-empty parent, (top cpuset
> + * has online cpus, so can't be empty).
> + */
> + parent = c->parent;
> + while (parent && cpus_empty(parent->cpus_allowed))
> + parent = parent->parent;
> + npids = atomic_read(&c->count);
> + /* c->count is the number of tasks using the cpuset */
> + if (npids)
> + /* move member tasks to the parent cpuset */
> + move_member_tasks_to_cpuset(c, parent);
> +
> + /*
> + * sanity check that we're not over-running
> + * the array
> + */
> + if (++ple_used > ple_count)
> + return;
> + ple = ple_array[(*ple_availp)++];
> + path = (char *)ple + sizeof(struct path_list_element);
> + if (cpuset_path(c, path,
> + PAGE_SIZE-sizeof(struct path_list_element)) < 0)
> + path = NULL;
> + if (path != NULL) {
> + /*
> + * add path to list of cpusets to remove
> + * (list includes cpusets that are not
> + * notify-on-release)
> + */
> + ple->path = path;
> + ple->cs = c;
> + /*
> + * since we're walking "up" the tree, list
> + * any empty cpusets we find on the tail of
> + * the list (later==higher; start with lower)
> + */
> + list_add_tail(&ple->list, empty_list);
> + }
> + }
> + }
> +}
> +
> +/*
> + * Walk the specified cpuset subtree and remove any offline cpus from
> + * each cpuset.
> + *
> + * Count the number of empty cpusets.
> + *
> + * Call with both manage_mutex and callback_mutex held so
> + * that this function can modify cpus_allowed and mems_allowed.
> + *
> + * Recursive, on depth of cpuset subtree.
Recursive with what limit/bound?
at least realistically if not in source code.
and will that be reasonable 5 years from now,
without causing stack overflow?
Not that this function uses lots of stack, but I didn't track
down the call tree to get here.
> + */
> +
> +static void remove_offlines_count_emptys(const struct cpuset *cur, int *count)
> {
> struct cpuset *c;
>
> - /* Each of our child cpusets mems must be online */
> list_for_each_entry(c, &cur->children, sibling) {
> - guarantee_online_cpus_mems_in_subtree(c);
> - if (!cpus_empty(c->cpus_allowed))
> - guarantee_online_cpus(c, &c->cpus_allowed);
> - if (!nodes_empty(c->mems_allowed))
> - guarantee_online_mems(c, &c->mems_allowed);
> + remove_offlines_count_emptys(c, count);
> + /* Remove offline cpus and mems from this cpuset. */
> + cpus_and(c->cpus_allowed, c->cpus_allowed, cpu_online_map);
> + nodes_and(c->mems_allowed, c->mems_allowed, node_online_map);
> + if (cpus_empty(c->cpus_allowed) ||
> + nodes_empty(c->mems_allowed))
> + (*count)++;
> }
> }
>
> @@ -2095,7 +2202,7 @@ static void guarantee_online_cpus_mems_i
> * To ensure that we don't remove a CPU or node from the top cpuset
> * that is currently in use by a child cpuset (which would violate
> * the rule that cpusets must be subsets of their parent), we first
> - * call the recursive routine guarantee_online_cpus_mems_in_subtree().
> + * call the recursive routine remove_tasks_in_empty_cpusets_in_subtree().
> *
> * Since there are two callers of this routine, one for CPU hotplug
> * events and one for memory node hotplug events, we could have coded
> @@ -2105,15 +2212,68 @@ static void guarantee_online_cpus_mems_i
>
> static void common_cpu_mem_hotplug_unplug(void)
> {
> + int i, empty_count=0, ple_avail=0;
> + struct list_head empty_cpuset_list;
> + struct path_list_element *ple, **ple_array=NULL;
> +
> mutex_lock(&manage_mutex);
> - mutex_lock(&callback_mutex);
>
> - guarantee_online_cpus_mems_in_subtree(&top_cpuset);
> + mutex_lock(&callback_mutex);
> top_cpuset.cpus_allowed = cpu_online_map;
> top_cpuset.mems_allowed = node_online_map;
> -
> + remove_offlines_count_emptys(&top_cpuset, &empty_count);
> mutex_unlock(&callback_mutex);
> +
> + if (empty_count) {
> + /*
> + * allocate the control structures needed for a list of
> + * cpuset paths to free. (allocation must be done without
> + * holding callback_mutex)
> + */
> + ple_array = (struct path_list_element **)kmalloc
cast not needed?
> + (empty_count*sizeof(struct empty_cpuset_list *), GFP_KERNEL);
> + if (!ple_array)
> + return;
> + for (i=0; i<empty_count; i++) {
Spaces: for (i = 0; i < empty_count; i++) {
> + ple = kmalloc(PAGE_SIZE, GFP_KERNEL);
> + /*
> + * the space for the path itself immediately follows
> + * the path_list_element structure (we have a full page)
> + */
> + if (!ple)
> + return;
> + ple_array[i]= ple;
> + }
> + INIT_LIST_HEAD(&empty_cpuset_list);
> +
> + mutex_lock(&callback_mutex);
> + remove_tasks_in_empty_cpusets_in_subtree(&top_cpuset,
> + &empty_cpuset_list, ple_array, &ple_avail, empty_count);
> + mutex_unlock(&callback_mutex);
> + }
> +
> mutex_unlock(&manage_mutex);
> +
> + if (empty_count) {
> + /*
> + * Free each cpuset on the list.
> + * (but only if it is notify-on-release)
> + */
> + list_for_each_entry(ple, &empty_cpuset_list, list) {
> + if (notify_on_release(ple->cs))
> + cpuset_release_agent(ple->path, 0);
> + /*
> + * 0: don't ask cpuset_release_agent to
> + * release the path
> + */
Don't explain function parameters unless they are tricky.
> + }
> + /* remove the control structures */
> + for (i=0; i<empty_count; i++) {
spacing
> + kfree(ple_array[i]);
> + }
> + kfree(ple_array);
> + }
> + return;
> }
>
> /*
> @@ -2259,7 +2419,7 @@ void cpuset_exit(struct task_struct *tsk
> if (atomic_dec_and_test(&cs->count))
> check_for_release(cs, &pathbuf);
> mutex_unlock(&manage_mutex);
> - cpuset_release_agent(pathbuf);
> + cpuset_release_agent(pathbuf, 1);
> } else {
> atomic_dec(&cs->count);
> }
---
~Randy
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