Messages in this thread Patch in this message | | | Date | Thu, 25 Sep 2008 15:27:22 +0900 | From | KAMEZAWA Hiroyuki <> | Subject | [PATCH 7/12] memcg add function to move account |
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This patch provides a function to move account information of a page between mem_cgroups.
This moving of page_cgroup is done under - lru_lock of source/destination mem_cgroup is held. - lock_page_cgroup() is held.
Then, a routine which touches pc->mem_cgroup without lock_page_cgroup() should confirm pc->mem_cgroup is still valid or not. Typlical code can be following.
(while page is not under lock_page()) mem = pc->mem_cgroup; mz = page_cgroup_zoneinfo(pc) spin_lock_irqsave(&mz->lru_lock); if (pc->mem_cgroup == mem) ...../* some list handling */ spin_unlock_irq(&mz->lru_lock);
Or better way is lock_page_cgroup(pc); .... unlock_page_cgroup(pc);
But you should confirm the nest of lock and avoid deadlock. (trylock is better if it's ok.)
If you find page_cgroup from mem_cgroup's LRU under mz->lru_lock, you don't have to worry about what pc->mem_cgroup points to.
Changelog: (v4) -> (v5) - check for lock_page() is removed. - rewrote description.
Changelog: (v2) -> (v4) - added lock_page_cgroup(). - splitted out from new-force-empty patch. - added how-to-use text. - fixed race in __mem_cgroup_uncharge_common().
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
mm/memcontrol.c | 84 ++++++++++++++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 81 insertions(+), 3 deletions(-)
Index: mmotm-2.6.27-rc7+/mm/memcontrol.c =================================================================== --- mmotm-2.6.27-rc7+.orig/mm/memcontrol.c +++ mmotm-2.6.27-rc7+/mm/memcontrol.c @@ -426,6 +426,7 @@ int task_in_mem_cgroup(struct task_struc void mem_cgroup_move_lists(struct page *page, enum lru_list lru) { struct page_cgroup *pc; + struct mem_cgroup *mem; struct mem_cgroup_per_zone *mz; unsigned long flags; @@ -444,9 +445,14 @@ void mem_cgroup_move_lists(struct page * pc = page_get_page_cgroup(page); if (pc) { + mem = pc->mem_cgroup; mz = page_cgroup_zoneinfo(pc); spin_lock_irqsave(&mz->lru_lock, flags); - __mem_cgroup_move_lists(pc, lru); + /* + * check against the race with move_account. + */ + if (likely(mem == pc->mem_cgroup)) + __mem_cgroup_move_lists(pc, lru); spin_unlock_irqrestore(&mz->lru_lock, flags); } unlock_page_cgroup(page); @@ -567,6 +573,70 @@ unsigned long mem_cgroup_isolate_pages(u return nr_taken; } +/** + * mem_cgroup_move_account - move account of the page + * @page ... the target page of being moved. + * @pc ... page_cgroup of the page. + * @from ... mem_cgroup which the page is moved from. + * @to ... mem_cgroup which the page is moved to. + * + * The caller must confirm following. + * 1. disable irq. + * 2. lru_lock of old mem_cgroup should be held. + * 3. pc is guaranteed to be valid and on mem_cgroup's LRU. + * + * Because we cannot call try_to_free_page() here, the caller must guarantee + * this moving of charge never fails. (if charge fails, this call fails.) + * Currently this is called only against root cgroup. + * which has no limitation of resource. + * Returns 0 at success, returns 1 at failure. + */ +int mem_cgroup_move_account(struct page *page, struct page_cgroup *pc, + struct mem_cgroup *from, struct mem_cgroup *to) +{ + struct mem_cgroup_per_zone *from_mz, *to_mz; + int nid, zid; + int ret = 1; + + VM_BUG_ON(!irqs_disabled()); + + nid = page_to_nid(page); + zid = page_zonenum(page); + from_mz = mem_cgroup_zoneinfo(from, nid, zid); + to_mz = mem_cgroup_zoneinfo(to, nid, zid); + + if (res_counter_charge(&to->res, PAGE_SIZE)) { + /* Now, we assume no_limit...no failure here. */ + return ret; + } + if (!try_lock_page_cgroup(page)) { + res_counter_uncharge(&to->res, PAGE_SIZE); + return ret; + } + + if (page_get_page_cgroup(page) != pc) { + res_counter_uncharge(&to->res, PAGE_SIZE); + goto out; + } + + if (spin_trylock(&to_mz->lru_lock)) { + __mem_cgroup_remove_list(from_mz, pc); + css_put(&from->css); + res_counter_uncharge(&from->res, PAGE_SIZE); + pc->mem_cgroup = to; + css_get(&to->css); + __mem_cgroup_add_list(to_mz, pc); + ret = 0; + spin_unlock(&to_mz->lru_lock); + } else { + res_counter_uncharge(&to->res, PAGE_SIZE); + } +out: + unlock_page_cgroup(page); + + return ret; +} + /* * Charge the memory controller for page usage. * Return @@ -754,16 +824,24 @@ __mem_cgroup_uncharge_common(struct page if ((ctype == MEM_CGROUP_CHARGE_TYPE_MAPPED) && ((PageCgroupCache(pc) || page_mapped(page)))) goto unlock; - +retry: + mem = pc->mem_cgroup; mz = page_cgroup_zoneinfo(pc); spin_lock_irqsave(&mz->lru_lock, flags); + if (ctype == MEM_CGROUP_CHARGE_TYPE_MAPPED && + unlikely(mem != pc->mem_cgroup)) { + /* MAPPED account can be done without lock_page(). + Check race with mem_cgroup_move_account() */ + spin_unlock_irqrestore(&mz->lru_lock, flags); + goto retry; + } __mem_cgroup_remove_list(mz, pc); spin_unlock_irqrestore(&mz->lru_lock, flags); page_assign_page_cgroup(page, NULL); unlock_page_cgroup(page); - mem = pc->mem_cgroup; + res_counter_uncharge(&mem->res, PAGE_SIZE); css_put(&mem->css);
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