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SubjectRe: [RFC][-mm] Memory controller hierarchy support (v1)
Balbir Singh wrote:
> This applies on top of 2.6.25-rc8-mm2. The next version will be applied
> on top of 2.5.25-mm1.
>
> This code is built on top of Pavel's hierarchy patches.
>
> 1. It propagates the charges upwards. A charge incurred on a cgroup
> is propagated to root. If any of the counters along the hierarchy
> is over limit, reclaim is initiated from the parent. We reclaim
> pages from the parent and the children below it. We also keep track
> of the last child from whom reclaim was done and start from there in
> the next reclaim.

Are you going to split this patch? As is it looks rather huge :)

> TODO's/Open Questions
>
> 1. We need to hold cgroup_mutex while walking through the children
> in reclaim. We need to figure out the best way to do so. Should
> cgroups provide a helper function/macro for it?
> 2. Do not allow children to have a limit greater than their parents.
> 3. Allow the user to select if hierarchial support is required
> 4. Fine tune reclaim from children logic
>
> Testing
>
> This code was tested on a UML instance, where it compiled and worked well.
>
> Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
> Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com>
> ---
>
> include/linux/res_counter.h | 14 ++++
> kernel/res_counter.c | 42 +++++++++++---
> mm/memcontrol.c | 128 +++++++++++++++++++++++++++++++++++---------
> 3 files changed, 148 insertions(+), 36 deletions(-)
>
> diff -puN include/linux/res_counter.h~memory-controller-hierarchy-support include/linux/res_counter.h
> --- linux-2.6.25-rc8/include/linux/res_counter.h~memory-controller-hierarchy-support 2008-04-19 11:00:28.000000000 +0530
> +++ linux-2.6.25-rc8-balbir/include/linux/res_counter.h 2008-04-19 11:00:28.000000000 +0530
> @@ -43,6 +43,10 @@ struct res_counter {
> * the routines below consider this to be IRQ-safe
> */
> spinlock_t lock;
> + /*
> + * the parent counter. used for hierarchical resource accounting
> + */
> + struct res_counter *parent;
> };
>
> /**
> @@ -82,7 +86,12 @@ enum {
> * helpers for accounting
> */
>
> -void res_counter_init(struct res_counter *counter);
> +/*
> + * the parent pointer is set only once - during the counter
> + * initialization. caller then must itself provide that this
> + * pointer is valid during the new counter lifetime
> + */
> +void res_counter_init(struct res_counter *counter, struct res_counter *parent);
>
> /*
> * charge - try to consume more resource.
> @@ -96,7 +105,8 @@ void res_counter_init(struct res_counter
> */
>
> int res_counter_charge_locked(struct res_counter *counter, unsigned long val);
> -int res_counter_charge(struct res_counter *counter, unsigned long val);
> +int res_counter_charge(struct res_counter *counter, unsigned long val,
> + struct res_counter **limit_exceeded_at);
>
> /*
> * uncharge - tell that some portion of the resource is released
> diff -puN kernel/res_counter.c~memory-controller-hierarchy-support kernel/res_counter.c
> --- linux-2.6.25-rc8/kernel/res_counter.c~memory-controller-hierarchy-support 2008-04-19 11:00:28.000000000 +0530
> +++ linux-2.6.25-rc8-balbir/kernel/res_counter.c 2008-04-19 11:00:28.000000000 +0530
> @@ -14,10 +14,11 @@
> #include <linux/res_counter.h>
> #include <linux/uaccess.h>
>
> -void res_counter_init(struct res_counter *counter)
> +void res_counter_init(struct res_counter *counter, struct res_counter *parent)
> {
> spin_lock_init(&counter->lock);
> counter->limit = (unsigned long long)LLONG_MAX;
> + counter->parent = parent;
> }
>
> int res_counter_charge_locked(struct res_counter *counter, unsigned long val)
> @@ -33,14 +34,34 @@ int res_counter_charge_locked(struct res
> return 0;
> }
>
> -int res_counter_charge(struct res_counter *counter, unsigned long val)
> +int res_counter_charge(struct res_counter *counter, unsigned long val,
> + struct res_counter **limit_exceeded_at)
> {
> int ret;
> unsigned long flags;
> + struct res_counter *c, *unroll_c;
>
> - spin_lock_irqsave(&counter->lock, flags);
> - ret = res_counter_charge_locked(counter, val);
> - spin_unlock_irqrestore(&counter->lock, flags);
> + *limit_exceeded_at = NULL;
> + local_irq_save(flags);
> + for (c = counter; c != NULL; c = c->parent) {
> + spin_lock(&c->lock);
> + ret = res_counter_charge_locked(c, val);
> + spin_unlock(&c->lock);
> + if (ret < 0) {
> + *limit_exceeded_at = c;
> + goto unroll;
> + }
> + }
> + local_irq_restore(flags);
> + return 0;
> +
> +unroll:
> + for (unroll_c = counter; unroll_c != c; unroll_c = unroll_c->parent) {
> + spin_lock(&unroll_c->lock);
> + res_counter_uncharge_locked(unroll_c, val);
> + spin_unlock(&unroll_c->lock);
> + }
> + local_irq_restore(flags);
> return ret;
> }
>
> @@ -55,10 +76,15 @@ void res_counter_uncharge_locked(struct
> void res_counter_uncharge(struct res_counter *counter, unsigned long val)
> {
> unsigned long flags;
> + struct res_counter *c;
>
> - spin_lock_irqsave(&counter->lock, flags);
> - res_counter_uncharge_locked(counter, val);
> - spin_unlock_irqrestore(&counter->lock, flags);
> + local_irq_save(flags);
> + for (c = counter; c != NULL; c = c->parent) {
> + spin_lock(&c->lock);
> + res_counter_uncharge_locked(c, val);
> + spin_unlock(&c->lock);
> + }
> + local_irq_restore(flags);
> }
>
>
> diff -puN mm/memcontrol.c~memory-controller-hierarchy-support mm/memcontrol.c
> --- linux-2.6.25-rc8/mm/memcontrol.c~memory-controller-hierarchy-support 2008-04-19 11:00:28.000000000 +0530
> +++ linux-2.6.25-rc8-balbir/mm/memcontrol.c 2008-04-19 11:00:28.000000000 +0530
> @@ -138,6 +138,13 @@ struct mem_cgroup {
> * statistics.
> */
> struct mem_cgroup_stat stat;
> +
> + /*
> + * When reclaiming in a hierarchy, we need to know, which child
> + * we reclaimed last from. This helps us avoid hitting the first
> + * child over and over again
> + */
> + struct mem_cgroup *last_scanned_child;
> };
> static struct mem_cgroup init_mem_cgroup;
>
> @@ -244,6 +251,12 @@ struct mem_cgroup *mem_cgroup_from_task(
> struct mem_cgroup, css);
> }
>
> +static struct mem_cgroup*
> +mem_cgroup_from_res_counter(struct res_counter *counter)
> +{
> + return container_of(counter, struct mem_cgroup, res);
> +}
> +
> static inline int page_cgroup_locked(struct page *page)
> {
> return bit_spin_is_locked(PAGE_CGROUP_LOCK_BIT, &page->page_cgroup);
> @@ -508,6 +521,86 @@ unsigned long mem_cgroup_isolate_pages(u
> }
>
> /*
> + * Charge mem and check if it is over it's limit. If so, reclaim from
> + * mem. This function can call itself recursively (as we walk up the
> + * hierarchy).
> + */
> +static int mem_cgroup_charge_and_reclaim(struct mem_cgroup *mem, gfp_t gfp_mask)
> +{
> + int ret = 0;
> + unsigned long nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
> + struct res_counter *counter_over_limit;
> + struct mem_cgroup *mem_over_limit;
> + struct cgroup *cgroup, *cgrp, *curr_cgroup;
> +
> + while (res_counter_charge(&mem->res, PAGE_SIZE, &counter_over_limit)) {
> + if (!(gfp_mask & __GFP_WAIT))
> + goto out;
> +
> + /*
> + * Is one of our ancestors over limit ?
> + */
> + if (counter_over_limit) {
> + mem_over_limit =
> + mem_cgroup_from_res_counter(counter_over_limit);
> +
> + if (mem != mem_over_limit)
> + ret = mem_cgroup_charge_and_reclaim(
> + mem_over_limit, gfp_mask);
> + }
> +
> + if (try_to_free_mem_cgroup_pages(mem, gfp_mask))
> + continue;
> +
> + /*
> + * try_to_free_mem_cgroup_pages() might not give us a full
> + * picture of reclaim. Some pages are reclaimed and might be
> + * moved to swap cache or just unmapped from the cgroup.
> + * Check the limit again to see if the reclaim reduced the
> + * current usage of the cgroup before giving up
> + */
> + if (res_counter_check_under_limit(&mem->res))
> + continue;
> +
> + /*
> + * Now scan all children under the group. This is required
> + * to support hierarchies
> + */
> + if (!mem->last_scanned_child)
> + cgroup = list_first_entry(&mem->css.cgroup->children,
> + struct cgroup, sibling);
> + else
> + cgroup = mem->last_scanned_child->css.cgroup;
> +
> + curr_cgroup = mem->css.cgroup;
> +
> + /*
> + * Ideally we need to hold cgroup_mutex here
> + */
> + list_for_each_entry_safe_from(cgroup, cgrp,
> + &curr_cgroup->children, sibling) {
> + struct mem_cgroup *mem_child;
> +
> + mem_child = mem_cgroup_from_cont(cgroup);
> + ret = try_to_free_mem_cgroup_pages(mem_child,
> + gfp_mask);
> + mem->last_scanned_child = mem_child;
> + if (ret == 0)
> + break;
> + }
> +
> + if (!nr_retries--) {
> + mem_cgroup_out_of_memory(mem, gfp_mask);
> + ret = -ENOMEM;
> + break;
> + }
> + }
> +
> +out:
> + return ret;
> +}
> +
> +/*
> * Charge the memory controller for page usage.
> * Return
> * 0 if the charge was successful
> @@ -519,7 +612,6 @@ static int mem_cgroup_charge_common(stru
> struct mem_cgroup *mem;
> struct page_cgroup *pc;
> unsigned long flags;
> - unsigned long nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
> struct mem_cgroup_per_zone *mz;
>
> if (mem_cgroup_subsys.disabled)
> @@ -570,28 +662,8 @@ retry:
> css_get(&mem->css);
> rcu_read_unlock();
>
> - while (res_counter_charge(&mem->res, PAGE_SIZE)) {
> - if (!(gfp_mask & __GFP_WAIT))
> - goto out;
> -
> - if (try_to_free_mem_cgroup_pages(mem, gfp_mask))
> - continue;
> -
> - /*
> - * try_to_free_mem_cgroup_pages() might not give us a full
> - * picture of reclaim. Some pages are reclaimed and might be
> - * moved to swap cache or just unmapped from the cgroup.
> - * Check the limit again to see if the reclaim reduced the
> - * current usage of the cgroup before giving up
> - */
> - if (res_counter_check_under_limit(&mem->res))
> - continue;
> -
> - if (!nr_retries--) {
> - mem_cgroup_out_of_memory(mem, gfp_mask);
> - goto out;
> - }
> - }
> + if (mem_cgroup_charge_and_reclaim(mem, gfp_mask))
> + goto out;
>
> pc->ref_cnt = 1;
> pc->mem_cgroup = mem;
> @@ -986,19 +1058,23 @@ static void free_mem_cgroup_per_zone_inf
> static struct cgroup_subsys_state *
> mem_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cont)
> {
> - struct mem_cgroup *mem;
> + struct mem_cgroup *mem, *parent;
> int node;
>
> if (unlikely((cont->parent) == NULL)) {
> mem = &init_mem_cgroup;
> page_cgroup_cache = KMEM_CACHE(page_cgroup, SLAB_PANIC);
> - } else
> + parent = NULL;
> + } else {
> mem = kzalloc(sizeof(struct mem_cgroup), GFP_KERNEL);
> + parent = mem_cgroup_from_cont(cont->parent);
> + }
>
> if (mem == NULL)
> return ERR_PTR(-ENOMEM);
>
> - res_counter_init(&mem->res);
> + res_counter_init(&mem->res, parent ? &parent->res : NULL);
> + mem->last_scanned_child = NULL;

I though about it recently. Can we have a cgroup file, which will
control whether to attach a res_counter to the parent? This will
address the YEMEMOTO's question about the performance.

> memset(&mem->info, 0, sizeof(mem->info));
>
> _
>



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