Messages in this thread | | | Date | Fri, 26 Sep 2008 18:24:42 +0900 | From | KAMEZAWA Hiroyuki <> | Subject | Re: [PATCH 7/12] memcg add function to move account |
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On Fri, 26 Sep 2008 16:30:50 +0900 Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:
> > @@ -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. > you're right.
Thanks, -Kame
> > 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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