Messages in this thread | | | Date | Fri, 26 Sep 2008 16:30:50 +0900 | From | Daisuke Nishimura <> | Subject | Re: [PATCH 7/12] memcg add function to move account |
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> @@ -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);
(snip)
> @@ -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; > + }
I'm sorry, but I've not been convinced yet why these checks are needed here. (Those checks are removed by [9/12] anyway.)
IIUC, pc->mem_cgroup is moved to another group only by mem_cgroup_move_account under lock_page_cgroup( and mz->lru_lock). And those two above(mem_cgroup_move_lists and __mem_cgroup_uncharge_common) sets mem = pc->mem_cgroup under lock_page_cgroup, so I don't think those checks (mem != pc->mem_cgroup) is needed.
Thanks, Daisuke Nishimura.
> +/** > + * 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 > __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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