memcg: clean up memory thresholds

Introduce struct mem_cgroup_thresholds.  It helps to reduce number of
checks of thresholds type (memory or mem+swap).

[akpm@linux-foundation.org: repair comment]
Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>
Cc: Phil Carmody <ext-phil.2.carmody@nokia.com>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: Paul Menage <menage@google.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index a4172a8..c6ece0a 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -158,6 +158,18 @@ struct mem_cgroup_threshold_ary {
        /* Array of thresholds */
        struct mem_cgroup_threshold entries[0];
 };
+
+struct mem_cgroup_thresholds {
+       /* Primary thresholds array */
+       struct mem_cgroup_threshold_ary *primary;
+       /*
+        * Spare threshold array.
+        * This is needed to make mem_cgroup_unregister_event() "never fail".
+        * It must be able to store at least primary->size - 1 entries.
+        */
+       struct mem_cgroup_threshold_ary *spare;
+};
+
 /* for OOM */
 struct mem_cgroup_eventfd_list {
        struct list_head list;
@@ -224,20 +236,10 @@ struct mem_cgroup {
        struct mutex thresholds_lock;
 
        /* thresholds for memory usage. RCU-protected */
-       struct mem_cgroup_threshold_ary *thresholds;
-
-       /*
-        * Preallocated buffer to be used in mem_cgroup_unregister_event()
-        * to make it "never fail".
-        * It must be able to store at least thresholds->size - 1 entries.
-        */
-       struct mem_cgroup_threshold_ary *__thresholds;
+       struct mem_cgroup_thresholds thresholds;
 
        /* thresholds for mem+swap usage. RCU-protected */
-       struct mem_cgroup_threshold_ary *memsw_thresholds;
-
-       /* the same as __thresholds, but for memsw_thresholds */
-       struct mem_cgroup_threshold_ary *__memsw_thresholds;
+       struct mem_cgroup_thresholds memsw_thresholds;
 
        /* For oom notifier event fd */
        struct list_head oom_notify;
@@ -3467,9 +3469,9 @@ static void __mem_cgroup_threshold(struct mem_cgroup *memcg, bool swap)
 
        rcu_read_lock();
        if (!swap)
-               t = rcu_dereference(memcg->thresholds);
+               t = rcu_dereference(memcg->thresholds.primary);
        else
-               t = rcu_dereference(memcg->memsw_thresholds);
+               t = rcu_dereference(memcg->memsw_thresholds.primary);
 
        if (!t)
                goto unlock;
@@ -3543,91 +3545,78 @@ static int mem_cgroup_usage_register_event(struct cgroup *cgrp,
        struct cftype *cft, struct eventfd_ctx *eventfd, const char *args)
 {
        struct mem_cgroup *memcg = mem_cgroup_from_cont(cgrp);
-       struct mem_cgroup_threshold_ary *thresholds, *thresholds_new;
+       struct mem_cgroup_thresholds *thresholds;
+       struct mem_cgroup_threshold_ary *new;
        int type = MEMFILE_TYPE(cft->private);
        u64 threshold, usage;
-       int size;
-       int i, ret;
+       int i, size, ret;
 
        ret = res_counter_memparse_write_strategy(args, &threshold);
        if (ret)
                return ret;
 
        mutex_lock(&memcg->thresholds_lock);
+
        if (type == _MEM)
-               thresholds = memcg->thresholds;
+               thresholds = &memcg->thresholds;
        else if (type == _MEMSWAP)
-               thresholds = memcg->memsw_thresholds;
+               thresholds = &memcg->memsw_thresholds;
        else
                BUG();
 
        usage = mem_cgroup_usage(memcg, type == _MEMSWAP);
 
        /* Check if a threshold crossed before adding a new one */
-       if (thresholds)
+       if (thresholds->primary)
                __mem_cgroup_threshold(memcg, type == _MEMSWAP);
 
-       if (thresholds)
-               size = thresholds->size + 1;
-       else
-               size = 1;
+       size = thresholds->primary ? thresholds->primary->size + 1 : 1;
 
        /* Allocate memory for new array of thresholds */
-       thresholds_new = kmalloc(sizeof(*thresholds_new) +
-                       size * sizeof(struct mem_cgroup_threshold),
+       new = kmalloc(sizeof(*new) + size * sizeof(struct mem_cgroup_threshold),
                        GFP_KERNEL);
-       if (!thresholds_new) {
+       if (!new) {
                ret = -ENOMEM;
                goto unlock;
        }
-       thresholds_new->size = size;
+       new->size = size;
 
        /* Copy thresholds (if any) to new array */
-       if (thresholds)
-               memcpy(thresholds_new->entries, thresholds->entries,
-                               thresholds->size *
+       if (thresholds->primary) {
+               memcpy(new->entries, thresholds->primary->entries, (size - 1) *
                                sizeof(struct mem_cgroup_threshold));
+       }
+
        /* Add new threshold */
-       thresholds_new->entries[size - 1].eventfd = eventfd;
-       thresholds_new->entries[size - 1].threshold = threshold;
+       new->entries[size - 1].eventfd = eventfd;
+       new->entries[size - 1].threshold = threshold;
 
        /* Sort thresholds. Registering of new threshold isn't time-critical */
-       sort(thresholds_new->entries, size,
-                       sizeof(struct mem_cgroup_threshold),
+       sort(new->entries, size, sizeof(struct mem_cgroup_threshold),
                        compare_thresholds, NULL);
 
        /* Find current threshold */
-       thresholds_new->current_threshold = -1;
+       new->current_threshold = -1;
        for (i = 0; i < size; i++) {
-               if (thresholds_new->entries[i].threshold < usage) {
+               if (new->entries[i].threshold < usage) {
                        /*
-                        * thresholds_new->current_threshold will not be used
-                        * until rcu_assign_pointer(), so it's safe to increment
+                        * new->current_threshold will not be used until
+                        * rcu_assign_pointer(), so it's safe to increment
                         * it here.
                         */
-                       ++thresholds_new->current_threshold;
+                       ++new->current_threshold;
                }
        }
 
-       if (type == _MEM)
-               rcu_assign_pointer(memcg->thresholds, thresholds_new);
-       else
-               rcu_assign_pointer(memcg->memsw_thresholds, thresholds_new);
+       /* Free old spare buffer and save old primary buffer as spare */
+       kfree(thresholds->spare);
+       thresholds->spare = thresholds->primary;
+
+       rcu_assign_pointer(thresholds->primary, new);
 
        /* To be sure that nobody uses thresholds */
        synchronize_rcu();
 
-       /*
-        * Free old preallocated buffer and use thresholds as new
-        * preallocated buffer.
-        */
-       if (type == _MEM) {
-               kfree(memcg->__thresholds);
-               memcg->__thresholds = thresholds;
-       } else {
-               kfree(memcg->__memsw_thresholds);
-               memcg->__memsw_thresholds = thresholds;
-       }
 unlock:
        mutex_unlock(&memcg->thresholds_lock);
 
@@ -3638,17 +3627,17 @@ static void mem_cgroup_usage_unregister_event(struct cgroup *cgrp,
        struct cftype *cft, struct eventfd_ctx *eventfd)
 {
        struct mem_cgroup *memcg = mem_cgroup_from_cont(cgrp);
-       struct mem_cgroup_threshold_ary *thresholds, *thresholds_new;
+       struct mem_cgroup_thresholds *thresholds;
+       struct mem_cgroup_threshold_ary *new;
        int type = MEMFILE_TYPE(cft->private);
        u64 usage;
-       int size = 0;
-       int i, j;
+       int i, j, size;
 
        mutex_lock(&memcg->thresholds_lock);
        if (type == _MEM)
-               thresholds = memcg->thresholds;
+               thresholds = &memcg->thresholds;
        else if (type == _MEMSWAP)
-               thresholds = memcg->memsw_thresholds;
+               thresholds = &memcg->memsw_thresholds;
        else
                BUG();
 
@@ -3664,53 +3653,45 @@ static void mem_cgroup_usage_unregister_event(struct cgroup *cgrp,
        __mem_cgroup_threshold(memcg, type == _MEMSWAP);
 
        /* Calculate new number of threshold */
-       for (i = 0; i < thresholds->size; i++) {
-               if (thresholds->entries[i].eventfd != eventfd)
+       size = 0;
+       for (i = 0; i < thresholds->primary->size; i++) {
+               if (thresholds->primary->entries[i].eventfd != eventfd)
                        size++;
        }
 
-       /* Use preallocated buffer for new array of thresholds */
-       if (type == _MEM)
-               thresholds_new = memcg->__thresholds;
-       else
-               thresholds_new = memcg->__memsw_thresholds;
+       new = thresholds->spare;
 
        /* Set thresholds array to NULL if we don't have thresholds */
        if (!size) {
-               kfree(thresholds_new);
-               thresholds_new = NULL;
+               kfree(new);
+               new = NULL;
                goto swap_buffers;
        }
 
-       thresholds_new->size = size;
+       new->size = size;
 
        /* Copy thresholds and find current threshold */
-       thresholds_new->current_threshold = -1;
-       for (i = 0, j = 0; i < thresholds->size; i++) {
-               if (thresholds->entries[i].eventfd == eventfd)
+       new->current_threshold = -1;
+       for (i = 0, j = 0; i < thresholds->primary->size; i++) {
+               if (thresholds->primary->entries[i].eventfd == eventfd)
                        continue;
 
-               thresholds_new->entries[j] = thresholds->entries[i];
-               if (thresholds_new->entries[j].threshold < usage) {
+               new->entries[j] = thresholds->primary->entries[i];
+               if (new->entries[j].threshold < usage) {
                        /*
-                        * thresholds_new->current_threshold will not be used
+                        * new->current_threshold will not be used
                         * until rcu_assign_pointer(), so it's safe to increment
                         * it here.
                         */
-                       ++thresholds_new->current_threshold;
+                       ++new->current_threshold;
                }
                j++;
        }
 
 swap_buffers:
-       /* Swap thresholds array and preallocated buffer */
-       if (type == _MEM) {
-               memcg->__thresholds = thresholds;
-               rcu_assign_pointer(memcg->thresholds, thresholds_new);
-       } else {
-               memcg->__memsw_thresholds = thresholds;
-               rcu_assign_pointer(memcg->memsw_thresholds, thresholds_new);
-       }
+       /* Swap primary and spare array */
+       thresholds->spare = thresholds->primary;
+       rcu_assign_pointer(thresholds->primary, new);
 
        /* To be sure that nobody uses thresholds */
        synchronize_rcu();