From: Hirokazu Takahashi Date: Tue, 4 Mar 2008 22:29:15 +0000 (-0800) Subject: memcg: simplify force_empty and move_lists X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=9b3c0a07e0fca35e36751680de3e4c76dbff5df3;p=GitHub%2FLineageOS%2Fandroid_kernel_samsung_universal7580.git 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 Signed-off-by: Hugh Dickins Cc: David Rientjes Cc: Balbir Singh Cc: KAMEZAWA Hiroyuki Cc: YAMAMOTO Takashi Cc: Paul Menage Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/mm/memcontrol.c b/mm/memcontrol.c index dcbe30aad1d..f72067094e0 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -353,7 +353,6 @@ int task_in_mem_cgroup(struct task_struct *task, const struct mem_cgroup *mem) void mem_cgroup_move_lists(struct page *page, bool active) { struct page_cgroup *pc; - struct mem_cgroup *mem; struct mem_cgroup_per_zone *mz; unsigned long flags; @@ -367,35 +366,14 @@ void mem_cgroup_move_lists(struct page *page, bool active) if (!try_lock_page_cgroup(page)) return; - /* - * Now page_cgroup is stable, but we cannot acquire mz->lru_lock - * while holding it, because mem_cgroup_force_empty_list does the - * reverse. Get a hold on the mem_cgroup before unlocking, so that - * the zoneinfo remains stable, then take mz->lru_lock; then check - * that page still points to pc and pc (even if freed and reassigned - * to that same page meanwhile) still points to the same mem_cgroup. - * Then we know mz still points to the right spinlock, so it's safe - * to move_lists (page->page_cgroup might be reset while we do so, but - * that doesn't matter: pc->page is stable till we drop mz->lru_lock). - * We're being a little naughty not to try_lock_page_cgroup again - * inside there, but we are safe, aren't we? Aren't we? Whistle... - */ pc = page_get_page_cgroup(page); if (pc) { - mem = pc->mem_cgroup; mz = page_cgroup_zoneinfo(pc); - css_get(&mem->css); - - unlock_page_cgroup(page); - spin_lock_irqsave(&mz->lru_lock, flags); - if (page_get_page_cgroup(page) == pc && pc->mem_cgroup == mem) - __mem_cgroup_move_lists(pc, active); + __mem_cgroup_move_lists(pc, active); spin_unlock_irqrestore(&mz->lru_lock, flags); - - css_put(&mem->css); - } else - unlock_page_cgroup(page); + } + unlock_page_cgroup(page); } /* @@ -789,7 +767,7 @@ static void mem_cgroup_force_empty_list(struct mem_cgroup *mem, { struct page_cgroup *pc; struct page *page; - int count; + int count = FORCE_UNCHARGE_BATCH; unsigned long flags; struct list_head *list; @@ -798,35 +776,21 @@ static void mem_cgroup_force_empty_list(struct mem_cgroup *mem, else list = &mz->inactive_list; - if (list_empty(list)) - return; -retry: - count = FORCE_UNCHARGE_BATCH; spin_lock_irqsave(&mz->lru_lock, flags); - - while (--count && !list_empty(list)) { + while (!list_empty(list)) { pc = list_entry(list->prev, struct page_cgroup, lru); page = pc->page; - lock_page_cgroup(page); - if (page_get_page_cgroup(page) == pc) { - page_assign_page_cgroup(page, NULL); - unlock_page_cgroup(page); - __mem_cgroup_remove_list(pc); - res_counter_uncharge(&mem->res, PAGE_SIZE); - css_put(&mem->css); - kfree(pc); - } else { - /* racing uncharge: let page go then retry */ - unlock_page_cgroup(page); - break; + get_page(page); + spin_unlock_irqrestore(&mz->lru_lock, flags); + mem_cgroup_uncharge_page(page); + put_page(page); + if (--count <= 0) { + count = FORCE_UNCHARGE_BATCH; + cond_resched(); } + spin_lock_irqsave(&mz->lru_lock, flags); } - spin_unlock_irqrestore(&mz->lru_lock, flags); - if (!list_empty(list)) { - cond_resched(); - goto retry; - } } /*