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SubjectRe: [patch 04/10] mm: memcg: per-priority per-zone hierarchy scan generations
[linux-foundation.org seems to be down, so I have changed Andrew's
address]

On Thu 29-09-11 23:00:58, Johannes Weiner wrote:
> Memory cgroup limit reclaim currently picks one memory cgroup out of
> the target hierarchy, remembers it as the last scanned child, and
> reclaims all zones in it with decreasing priority levels.
>
> The new hierarchy reclaim code will pick memory cgroups from the same
> hierarchy concurrently from different zones and priority levels, it
> becomes necessary that hierarchy roots not only remember the last
> scanned child, but do so for each zone and priority level.
>
> Until now, we reclaimed memcgs like this:
>
> mem = mem_cgroup_iter(root)
> for each priority level:
> for each zone in zonelist:
> reclaim(mem, zone)
>
> But subsequent patches will move the memcg iteration inside the loop
> over the zones:
>
> for each priority level:
> for each zone in zonelist:
> mem = mem_cgroup_iter(root)
> reclaim(mem, zone)
>
> And to keep with the original scan order - memcg -> priority -> zone -
> the last scanned memcg has to be remembered per zone and per priority
> level.
>
> Furthermore, global reclaim will be switched to the hierarchy walk as
> well. Different from limit reclaim, which can just recheck the limit
> after some reclaim progress, its target is to scan all memcgs for the
> desired zone pages, proportional to the memcg size, and so reliably
> detecting a full hierarchy round-trip will become crucial.
>
> Currently, the code relies on one reclaimer encountering the same
> memcg twice, but that is error-prone with concurrent reclaimers.
> Instead, use a generation counter that is increased every time the
> child with the highest ID has been visited, so that reclaimers can
> stop when the generation changes.

Both naming and the patch description is much nicer. Thanks!

>
> Signed-off-by: Johannes Weiner <jweiner@redhat.com>
> Reviewed-by: Kirill A. Shutemov <kirill@shutemov.name>

Reviewed-by: Michal Hocko <mhocko@suse.cz>

> ---
> mm/memcontrol.c | 65 +++++++++++++++++++++++++++++++++++++++---------------
> 1 files changed, 47 insertions(+), 18 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 0ba59f6..38d195d 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -121,6 +121,13 @@ struct mem_cgroup_stat_cpu {
> unsigned long targets[MEM_CGROUP_NTARGETS];
> };
>
> +struct mem_cgroup_reclaim_iter {
> + /* css_id of the last scanned hierarchy member */
> + int position;
> + /* scan generation, increased every round-trip */
> + unsigned int generation;
> +};
> +
> /*
> * per-zone information in memory controller.
> */
> @@ -131,6 +138,8 @@ struct mem_cgroup_per_zone {
> struct list_head lists[NR_LRU_LISTS];
> unsigned long count[NR_LRU_LISTS];
>
> + struct mem_cgroup_reclaim_iter reclaim_iter[DEF_PRIORITY + 1];
> +
> struct zone_reclaim_stat reclaim_stat;
> struct rb_node tree_node; /* RB tree node */
> unsigned long long usage_in_excess;/* Set to the value by which */
> @@ -231,11 +240,6 @@ struct mem_cgroup {
> * per zone LRU lists.
> */
> struct mem_cgroup_lru_info info;
> - /*
> - * While reclaiming in a hierarchy, we cache the last child we
> - * reclaimed from.
> - */
> - int last_scanned_child;
> int last_scanned_node;
> #if MAX_NUMNODES > 1
> nodemask_t scan_nodes;
> @@ -781,9 +785,16 @@ struct mem_cgroup *try_get_mem_cgroup_from_mm(struct mm_struct *mm)
> return memcg;
> }
>
> -static struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root,
> - struct mem_cgroup *prev,
> - bool reclaim)
> +struct mem_cgroup_reclaim_cookie {
> + struct zone *zone;
> + int priority;
> + unsigned int generation;
> +};
> +
> +static struct mem_cgroup *
> +mem_cgroup_iter(struct mem_cgroup *root,
> + struct mem_cgroup *prev,
> + struct mem_cgroup_reclaim_cookie *reclaim)
> {
> struct mem_cgroup *mem = NULL;
> int id = 0;
> @@ -804,10 +815,20 @@ static struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root,
> }
>
> while (!mem) {
> + struct mem_cgroup_reclaim_iter *uninitialized_var(iter);
> struct cgroup_subsys_state *css;
>
> - if (reclaim)
> - id = root->last_scanned_child;
> + if (reclaim) {
> + int nid = zone_to_nid(reclaim->zone);
> + int zid = zone_idx(reclaim->zone);
> + struct mem_cgroup_per_zone *mz;
> +
> + mz = mem_cgroup_zoneinfo(root, nid, zid);
> + iter = &mz->reclaim_iter[reclaim->priority];
> + if (prev && reclaim->generation != iter->generation)
> + return NULL;
> + id = iter->position;
> + }
>
> rcu_read_lock();
> css = css_get_next(&mem_cgroup_subsys, id + 1, &root->css, &id);
> @@ -818,8 +839,13 @@ static struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root,
> id = 0;
> rcu_read_unlock();
>
> - if (reclaim)
> - root->last_scanned_child = id;
> + if (reclaim) {
> + iter->position = id;
> + if (!css)
> + iter->generation++;
> + else if (!prev && mem)
> + reclaim->generation = iter->generation;
> + }
>
> if (prev && !css)
> return NULL;
> @@ -842,14 +868,14 @@ static void mem_cgroup_iter_break(struct mem_cgroup *root,
> * be used for reference counting.
> */
> #define for_each_mem_cgroup_tree(iter, root) \
> - for (iter = mem_cgroup_iter(root, NULL, false); \
> + for (iter = mem_cgroup_iter(root, NULL, NULL); \
> iter != NULL; \
> - iter = mem_cgroup_iter(root, iter, false))
> + iter = mem_cgroup_iter(root, iter, NULL))
>
> #define for_each_mem_cgroup(iter) \
> - for (iter = mem_cgroup_iter(NULL, NULL, false); \
> + for (iter = mem_cgroup_iter(NULL, NULL, NULL); \
> iter != NULL; \
> - iter = mem_cgroup_iter(NULL, iter, false))
> + iter = mem_cgroup_iter(NULL, iter, NULL))
>
> static inline bool mem_cgroup_is_root(struct mem_cgroup *memcg)
> {
> @@ -1619,6 +1645,10 @@ static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_memcg,
> bool check_soft = reclaim_options & MEM_CGROUP_RECLAIM_SOFT;
> unsigned long excess;
> unsigned long nr_scanned;
> + struct mem_cgroup_reclaim_cookie reclaim = {
> + .zone = zone,
> + .priority = 0,
> + };
>
> excess = res_counter_soft_limit_excess(&root_memcg->res) >> PAGE_SHIFT;
>
> @@ -1627,7 +1657,7 @@ static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_memcg,
> noswap = true;
>
> while (1) {
> - victim = mem_cgroup_iter(root_memcg, victim, true);
> + victim = mem_cgroup_iter(root_memcg, victim, &reclaim);
> if (!victim) {
> loop++;
> /*
> @@ -4878,7 +4908,6 @@ mem_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cont)
> res_counter_init(&memcg->res, NULL);
> res_counter_init(&memcg->memsw, NULL);
> }
> - memcg->last_scanned_child = 0;
> memcg->last_scanned_node = MAX_NUMNODES;
> INIT_LIST_HEAD(&memcg->oom_notify);
>
> --
> 1.7.6.2
>
> --
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--
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9
Czech Republic


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