This patch looks good to me, but I have one question. Why do we need to acquire sc.lock inside mem_cgroup_(start|end)_move() ? These functions doesn't access mc.*. Thanks, Daisuke Nishimura. On Fri, 20 Aug 2010 19:02:56 +0900 KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote: > No changes from v4. > == > From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> > > At accounting file events per memory cgroup, we need to find memory cgroup > via page_cgroup->mem_cgroup. Now, we use lock_page_cgroup(). > > But, considering the context which page-cgroup for files are accessed, > we can use alternative light-weight mutual execusion in the most case. > At handling file-caches, the only race we have to take care of is "moving" > account, IOW, overwriting page_cgroup->mem_cgroup. Because file status > update is done while the page-cache is in stable state, we don't have to > take care of race with charge/uncharge. > > Unlike charge/uncharge, "move" happens not so frequently. It happens only when > rmdir() and task-moving (with a special settings.) > This patch adds a race-checker for file-cache-status accounting v.s. account > moving. The new per-cpu-per-memcg counter MEM_CGROUP_ON_MOVE is added. > The routine for account move > 1. Increment it before start moving > 2. Call synchronize_rcu() > 3. Decrement it after the end of moving. > By this, file-status-counting routine can check it needs to call > lock_page_cgroup(). In most case, I doesn't need to call it. > > > Changelog: 20100804 > - added a comment for possible optimization hint. > Changelog: 20100730 > - some cleanup. > Changelog: 20100729 > - replaced __this_cpu_xxx() with this_cpu_xxx > (because we don't call spinlock) > - added VM_BUG_ON(). > > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> > --- > mm/memcontrol.c | 79 +++++++++++++++++++++++++++++++++++++++++++++++--------- > 1 file changed, 67 insertions(+), 12 deletions(-) > > Index: mmotm-0811/mm/memcontrol.c > =================================================================== > --- mmotm-0811.orig/mm/memcontrol.c > +++ mmotm-0811/mm/memcontrol.c > @@ -90,6 +90,7 @@ enum mem_cgroup_stat_index { > MEM_CGROUP_STAT_PGPGOUT_COUNT, /* # of pages paged out */ > MEM_CGROUP_STAT_SWAPOUT, /* # of pages, swapped out */ > MEM_CGROUP_EVENTS, /* incremented at every pagein/pageout */ > + MEM_CGROUP_ON_MOVE, /* A check for locking move account/status */ > > MEM_CGROUP_STAT_NSTATS, > }; > @@ -1086,7 +1087,50 @@ static unsigned int get_swappiness(struc > return swappiness; > } > > -/* A routine for testing mem is not under move_account */ > +static void mem_cgroup_start_move(struct mem_cgroup *mem) > +{ > + int cpu; > + /* for fast checking in mem_cgroup_update_file_stat() etc..*/ > + spin_lock(&mc.lock); > + /* TODO: Can we optimize this by for_each_online_cpu() ? */ > + for_each_possible_cpu(cpu) > + per_cpu(mem->stat->count[MEM_CGROUP_ON_MOVE], cpu) += 1; > + spin_unlock(&mc.lock); > + > + synchronize_rcu(); > +} > + > +static void mem_cgroup_end_move(struct mem_cgroup *mem) > +{ > + int cpu; > + > + if (!mem) > + return; > + /* for fast checking in mem_cgroup_update_file_stat() etc..*/ > + spin_lock(&mc.lock); > + for_each_possible_cpu(cpu) > + per_cpu(mem->stat->count[MEM_CGROUP_ON_MOVE], cpu) -= 1; > + spin_unlock(&mc.lock); > +} > + > +/* > + * mem_cgroup_is_moved -- checking a cgroup is mc.from target or not. > + * used for avoiding race. > + * mem_cgroup_under_move -- checking a cgroup is mc.from or mc.to or > + * under hierarchy of them. used for waiting at > + * memory pressure. > + * Result of is_moved can be trusted until the end of rcu_read_unlock(). > + * The caller must do > + * rcu_read_lock(); > + * result = mem_cgroup_is_moved(); > + * .....make use of result here.... > + * rcu_read_unlock(); > + */ > +static bool mem_cgroup_is_moved(struct mem_cgroup *mem) > +{ > + VM_BUG_ON(!rcu_read_lock_held()); > + return this_cpu_read(mem->stat->count[MEM_CGROUP_ON_MOVE]) > 0; > +} > > static bool mem_cgroup_under_move(struct mem_cgroup *mem) > { > @@ -1502,29 +1546,36 @@ void mem_cgroup_update_file_mapped(struc > { > struct mem_cgroup *mem; > struct page_cgroup *pc; > + bool need_lock = false; > > pc = lookup_page_cgroup(page); > if (unlikely(!pc)) > return; > - > - lock_page_cgroup(pc); > + rcu_read_lock(); > mem = id_to_memcg(pc->mem_cgroup, true); > - if (!mem || !PageCgroupUsed(pc)) > + if (likely(mem)) { > + if (mem_cgroup_is_moved(mem)) { > + /* need to serialize with move_account */ > + lock_page_cgroup(pc); > + need_lock = true; > + mem = id_to_memcg(pc->mem_cgroup, true); > + if (unlikely(!mem)) > + goto done; > + } > + } > + if (unlikely(!PageCgroupUsed(pc))) > goto done; > - > - /* > - * Preemption is already disabled. We can use __this_cpu_xxx > - */ > if (val > 0) { > - __this_cpu_inc(mem->stat->count[MEM_CGROUP_STAT_FILE_MAPPED]); > + this_cpu_inc(mem->stat->count[MEM_CGROUP_STAT_FILE_MAPPED]); > SetPageCgroupFileMapped(pc); > } else { > - __this_cpu_dec(mem->stat->count[MEM_CGROUP_STAT_FILE_MAPPED]); > + this_cpu_dec(mem->stat->count[MEM_CGROUP_STAT_FILE_MAPPED]); > ClearPageCgroupFileMapped(pc); > } > - > done: > - unlock_page_cgroup(pc); > + if (need_lock) > + unlock_page_cgroup(pc); > + rcu_read_unlock(); > } > > /* > @@ -3064,6 +3115,7 @@ move_account: > lru_add_drain_all(); > drain_all_stock_sync(); > ret = 0; > + mem_cgroup_start_move(mem); > for_each_node_state(node, N_HIGH_MEMORY) { > for (zid = 0; !ret && zid < MAX_NR_ZONES; zid++) { > enum lru_list l; > @@ -3077,6 +3129,7 @@ move_account: > if (ret) > break; > } > + mem_cgroup_end_move(mem); > memcg_oom_recover(mem); > /* it seems parent cgroup doesn't have enough mem */ > if (ret == -ENOMEM) > @@ -4563,6 +4616,7 @@ static void mem_cgroup_clear_mc(void) > mc.to = NULL; > mc.moving_task = NULL; > spin_unlock(&mc.lock); > + mem_cgroup_end_move(from); > memcg_oom_recover(from); > memcg_oom_recover(to); > wake_up_all(&mc.waitq); > @@ -4593,6 +4647,7 @@ static int mem_cgroup_can_attach(struct > VM_BUG_ON(mc.moved_charge); > VM_BUG_ON(mc.moved_swap); > VM_BUG_ON(mc.moving_task); > + mem_cgroup_start_move(from); > spin_lock(&mc.lock); > mc.from = from; > mc.to = mem; > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . 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