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SubjectRe: [PATCH 7/12] memcg add function to move account
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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