Re: [PATCH 4/13] memcg: force_empty moving account

Peter Zijlstra
2008-09-22T14:23:40Z

On Mon, 2008-09-22 at 20:00 +0900, KAMEZAWA Hiroyuki wrote:

> + /* For avoiding race with speculative page cache handling. */
> + if (!PageLRU(page) || !get_page_unless_zero(page)) {
> + list_move(&pc->lru, list);
> + spin_unlock_irqrestore(&mz->lru_lock, flags);
> + yield();

Gah, no way!

> + spin_lock_irqsave(&mz->lru_lock, flags);
> + continue;
> + }
> + if (!trylock_page(page)) {
> + list_move(&pc->lru, list);
> put_page(page);
> - if (--count <= 0) {
> - count = FORCE_UNCHARGE_BATCH;
> - cond_resched();
> - }
> - } else
> - cond_resched();
> - spin_lock_irqsave(&mz->lru_lock, flags);
> + spin_unlock_irqrestore(&mz->lru_lock, flags);
> + yield();

Seriously?!

> + spin_lock_irqsave(&mz->lru_lock, flags);
> + continue;
> + }
> + if (mem_cgroup_move_account(page, pc, mem, &init_mem_cgroup)) {
> + /* some confliction */
> + list_move(&pc->lru, list);
> + unlock_page(page);
> + put_page(page);
> + spin_unlock_irqrestore(&mz->lru_lock, flags);
> + yield();

Inflicting pain..

> + spin_lock_irqsave(&mz->lru_lock, flags);
> + } else {
> + unlock_page(page);
> + put_page(page);
> + }
> + if (atomic_read(&mem->css.cgroup->count) > 0)
> + break;
> }
> spin_unlock_irqrestore(&mz->lru_lock, flags);

do _NOT_ use yield() ever! unless you know what you're doing, and
probably not even then.

NAK!