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memcg: use css_tryget in memcg
From:KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
css_tryget() newly is added and we can know css is alive or not and get
refcnt of css in very safe way. ("alive" here means "rmdir/destroy" is
not called.)
This patch replaces css_get() to css_tryget(), where I cannot explain
why css_get() is safe. And removes memcg->obsolete flag.
Reviewed-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Paul Menage <menage@google.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
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>
This commit is contained in:
KAMEZAWA Hiroyuki
Linus Torvalds
parent
a7ba0eef3a
commit
54595fe265
@ -162,7 +162,6 @@ struct mem_cgroup {
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*/
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bool use_hierarchy;
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unsigned long last_oom_jiffies;
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int obsolete;
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atomic_t refcnt;
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unsigned int swappiness;
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@ -283,6 +282,31 @@ struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p)
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struct mem_cgroup, css);
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}
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static struct mem_cgroup *try_get_mem_cgroup_from_mm(struct mm_struct *mm)
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{
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struct mem_cgroup *mem = NULL;
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/*
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* Because we have no locks, mm->owner's may be being moved to other
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* cgroup. We use css_tryget() here even if this looks
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* pessimistic (rather than adding locks here).
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*/
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rcu_read_lock();
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do {
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mem = mem_cgroup_from_task(rcu_dereference(mm->owner));
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if (unlikely(!mem))
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break;
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} while (!css_tryget(&mem->css));
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rcu_read_unlock();
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return mem;
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}
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static bool mem_cgroup_is_obsolete(struct mem_cgroup *mem)
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{
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if (!mem)
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return true;
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return css_is_removed(&mem->css);
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}
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/*
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* Following LRU functions are allowed to be used without PCG_LOCK.
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* Operations are called by routine of global LRU independently from memcg.
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@ -622,8 +646,9 @@ mem_cgroup_get_first_node(struct mem_cgroup *root_mem)
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{
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struct cgroup *cgroup;
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struct mem_cgroup *ret;
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bool obsolete = (root_mem->last_scanned_child &&
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root_mem->last_scanned_child->obsolete);
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bool obsolete;
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obsolete = mem_cgroup_is_obsolete(root_mem->last_scanned_child);
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/*
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* Scan all children under the mem_cgroup mem
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@ -636,7 +661,7 @@ mem_cgroup_get_first_node(struct mem_cgroup *root_mem)
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if (!root_mem->last_scanned_child || obsolete) {
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if (obsolete)
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if (obsolete && root_mem->last_scanned_child)
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mem_cgroup_put(root_mem->last_scanned_child);
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cgroup = list_first_entry(&root_mem->css.cgroup->children,
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@ -711,7 +736,7 @@ static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_mem,
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next_mem = mem_cgroup_get_first_node(root_mem);
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while (next_mem != root_mem) {
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if (next_mem->obsolete) {
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if (mem_cgroup_is_obsolete(next_mem)) {
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mem_cgroup_put(next_mem);
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cgroup_lock();
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next_mem = mem_cgroup_get_first_node(root_mem);
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@ -769,23 +794,17 @@ static int __mem_cgroup_try_charge(struct mm_struct *mm,
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* thread group leader migrates. It's possible that mm is not
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* set, if so charge the init_mm (happens for pagecache usage).
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*/
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if (likely(!*memcg)) {
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rcu_read_lock();
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mem = mem_cgroup_from_task(rcu_dereference(mm->owner));
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if (unlikely(!mem)) {
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rcu_read_unlock();
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return 0;
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}
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/*
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* For every charge from the cgroup, increment reference count
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*/
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css_get(&mem->css);
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mem = *memcg;
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if (likely(!mem)) {
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mem = try_get_mem_cgroup_from_mm(mm);
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*memcg = mem;
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rcu_read_unlock();
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} else {
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mem = *memcg;
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css_get(&mem->css);
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}
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if (unlikely(!mem))
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return 0;
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VM_BUG_ON(mem_cgroup_is_obsolete(mem));
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while (1) {
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int ret;
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@ -1072,12 +1091,19 @@ int mem_cgroup_cache_charge(struct page *page, struct mm_struct *mm,
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MEM_CGROUP_CHARGE_TYPE_SHMEM, NULL);
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}
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/*
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* While swap-in, try_charge -> commit or cancel, the page is locked.
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* And when try_charge() successfully returns, one refcnt to memcg without
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* struct page_cgroup is aquired. This refcnt will be cumsumed by
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* "commit()" or removed by "cancel()"
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*/
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int mem_cgroup_try_charge_swapin(struct mm_struct *mm,
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struct page *page,
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gfp_t mask, struct mem_cgroup **ptr)
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{
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struct mem_cgroup *mem;
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swp_entry_t ent;
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int ret;
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if (mem_cgroup_disabled())
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return 0;
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@ -1096,10 +1122,15 @@ int mem_cgroup_try_charge_swapin(struct mm_struct *mm,
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ent.val = page_private(page);
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mem = lookup_swap_cgroup(ent);
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if (!mem || mem->obsolete)
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if (!mem)
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goto charge_cur_mm;
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if (!css_tryget(&mem->css))
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goto charge_cur_mm;
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*ptr = mem;
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return __mem_cgroup_try_charge(NULL, mask, ptr, true);
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ret = __mem_cgroup_try_charge(NULL, mask, ptr, true);
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/* drop extra refcnt from tryget */
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css_put(&mem->css);
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return ret;
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charge_cur_mm:
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if (unlikely(!mm))
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mm = &init_mm;
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@ -1130,13 +1161,18 @@ int mem_cgroup_cache_charge_swapin(struct page *page,
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ent.val = page_private(page);
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if (do_swap_account) {
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mem = lookup_swap_cgroup(ent);
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if (mem && mem->obsolete)
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mem = NULL;
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if (mem)
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mm = NULL;
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if (mem) {
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if (css_tryget(&mem->css))
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mm = NULL; /* charge to recorded */
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else
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mem = NULL; /* charge to current */
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}
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}
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ret = mem_cgroup_charge_common(page, mm, mask,
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MEM_CGROUP_CHARGE_TYPE_SHMEM, mem);
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/* drop extra refcnt from tryget */
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if (mem)
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css_put(&mem->css);
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if (!ret && do_swap_account) {
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/* avoid double counting */
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@ -1178,7 +1214,6 @@ void mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *ptr)
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struct mem_cgroup *memcg;
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memcg = swap_cgroup_record(ent, NULL);
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if (memcg) {
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/* If memcg is obsolete, memcg can be != ptr */
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res_counter_uncharge(&memcg->memsw, PAGE_SIZE);
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mem_cgroup_put(memcg);
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}
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@ -1421,14 +1456,9 @@ int mem_cgroup_shrink_usage(struct mm_struct *mm, gfp_t gfp_mask)
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if (!mm)
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return 0;
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rcu_read_lock();
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mem = mem_cgroup_from_task(rcu_dereference(mm->owner));
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if (unlikely(!mem)) {
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rcu_read_unlock();
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mem = try_get_mem_cgroup_from_mm(mm);
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if (unlikely(!mem))
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return 0;
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}
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css_get(&mem->css);
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rcu_read_unlock();
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do {
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progress = mem_cgroup_hierarchical_reclaim(mem, gfp_mask, true);
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@ -2086,9 +2116,6 @@ static struct mem_cgroup *mem_cgroup_alloc(void)
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* the number of reference from swap_cgroup and free mem_cgroup when
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* it goes down to 0.
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*
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* When mem_cgroup is destroyed, mem->obsolete will be set to 0 and
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* entry which points to this memcg will be ignore at swapin.
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*
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* Removal of cgroup itself succeeds regardless of refs from swap.
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*/
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@ -2174,7 +2201,6 @@ static void mem_cgroup_pre_destroy(struct cgroup_subsys *ss,
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struct cgroup *cont)
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{
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struct mem_cgroup *mem = mem_cgroup_from_cont(cont);
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mem->obsolete = 1;
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mem_cgroup_force_empty(mem, false);
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}
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