memcg: simplify force_empty and move_lists
As for force_empty, though this may not be the main topic here, mem_cgroup_force_empty_list() can be implemented simpler. It is possible to make the function just call mem_cgroup_uncharge_page() instead of releasing page_cgroups by itself. The tip is to call get_page() before invoking mem_cgroup_uncharge_page(), so the page won't be released during this function. Kamezawa-san points out that by the time mem_cgroup_uncharge_page() uncharges, the page might have been reassigned to an lru of a different mem_cgroup, and now be emptied from that; but Hugh claims that's okay, the end state is the same as when it hasn't gone to another list. And once force_empty stops taking lock_page_cgroup within mz->lru_lock, mem_cgroup_move_lists() can be simplified to take mz->lru_lock directly while holding page_cgroup lock (but still has to use try_lock_page_cgroup). Signed-off-by: Hirokazu Takahashi <taka@valinux.co.jp> Signed-off-by: Hugh Dickins <hugh@veritas.com> Cc: David Rientjes <rientjes@google.com> Cc: Balbir Singh <balbir@linux.vnet.ibm.com> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: YAMAMOTO Takashi <yamamoto@valinux.co.jp> Cc: Paul Menage <menage@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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@ -353,7 +353,6 @@ int task_in_mem_cgroup(struct task_struct *task, const struct mem_cgroup *mem)
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void mem_cgroup_move_lists(struct page *page, bool active)
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void mem_cgroup_move_lists(struct page *page, bool active)
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{
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{
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struct page_cgroup *pc;
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struct page_cgroup *pc;
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struct mem_cgroup *mem;
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struct mem_cgroup_per_zone *mz;
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struct mem_cgroup_per_zone *mz;
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unsigned long flags;
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unsigned long flags;
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@ -367,34 +366,13 @@ void mem_cgroup_move_lists(struct page *page, bool active)
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if (!try_lock_page_cgroup(page))
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if (!try_lock_page_cgroup(page))
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return;
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return;
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/*
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* Now page_cgroup is stable, but we cannot acquire mz->lru_lock
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* while holding it, because mem_cgroup_force_empty_list does the
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* reverse. Get a hold on the mem_cgroup before unlocking, so that
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* the zoneinfo remains stable, then take mz->lru_lock; then check
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* that page still points to pc and pc (even if freed and reassigned
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* to that same page meanwhile) still points to the same mem_cgroup.
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* Then we know mz still points to the right spinlock, so it's safe
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* to move_lists (page->page_cgroup might be reset while we do so, but
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* that doesn't matter: pc->page is stable till we drop mz->lru_lock).
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* We're being a little naughty not to try_lock_page_cgroup again
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* inside there, but we are safe, aren't we? Aren't we? Whistle...
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*/
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pc = page_get_page_cgroup(page);
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pc = page_get_page_cgroup(page);
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if (pc) {
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if (pc) {
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mem = pc->mem_cgroup;
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mz = page_cgroup_zoneinfo(pc);
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mz = page_cgroup_zoneinfo(pc);
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css_get(&mem->css);
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unlock_page_cgroup(page);
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spin_lock_irqsave(&mz->lru_lock, flags);
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spin_lock_irqsave(&mz->lru_lock, flags);
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if (page_get_page_cgroup(page) == pc && pc->mem_cgroup == mem)
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__mem_cgroup_move_lists(pc, active);
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__mem_cgroup_move_lists(pc, active);
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spin_unlock_irqrestore(&mz->lru_lock, flags);
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spin_unlock_irqrestore(&mz->lru_lock, flags);
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}
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css_put(&mem->css);
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} else
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unlock_page_cgroup(page);
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unlock_page_cgroup(page);
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}
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}
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@ -789,7 +767,7 @@ static void mem_cgroup_force_empty_list(struct mem_cgroup *mem,
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{
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{
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struct page_cgroup *pc;
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struct page_cgroup *pc;
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struct page *page;
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struct page *page;
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int count;
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int count = FORCE_UNCHARGE_BATCH;
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unsigned long flags;
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unsigned long flags;
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struct list_head *list;
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struct list_head *list;
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@ -798,35 +776,21 @@ static void mem_cgroup_force_empty_list(struct mem_cgroup *mem,
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else
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else
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list = &mz->inactive_list;
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list = &mz->inactive_list;
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if (list_empty(list))
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return;
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retry:
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count = FORCE_UNCHARGE_BATCH;
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spin_lock_irqsave(&mz->lru_lock, flags);
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spin_lock_irqsave(&mz->lru_lock, flags);
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while (!list_empty(list)) {
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while (--count && !list_empty(list)) {
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pc = list_entry(list->prev, struct page_cgroup, lru);
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pc = list_entry(list->prev, struct page_cgroup, lru);
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page = pc->page;
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page = pc->page;
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lock_page_cgroup(page);
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get_page(page);
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if (page_get_page_cgroup(page) == pc) {
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page_assign_page_cgroup(page, NULL);
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unlock_page_cgroup(page);
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__mem_cgroup_remove_list(pc);
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res_counter_uncharge(&mem->res, PAGE_SIZE);
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css_put(&mem->css);
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kfree(pc);
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} else {
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/* racing uncharge: let page go then retry */
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unlock_page_cgroup(page);
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break;
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}
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}
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spin_unlock_irqrestore(&mz->lru_lock, flags);
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spin_unlock_irqrestore(&mz->lru_lock, flags);
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if (!list_empty(list)) {
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mem_cgroup_uncharge_page(page);
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put_page(page);
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if (--count <= 0) {
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count = FORCE_UNCHARGE_BATCH;
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cond_resched();
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cond_resched();
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goto retry;
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}
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}
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spin_lock_irqsave(&mz->lru_lock, flags);
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}
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spin_unlock_irqrestore(&mz->lru_lock, flags);
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}
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}
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/*
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/*
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