Re: [PATCH v1 10/14] mm: multigenerational lru: core

[Andi Kleen]

Yu Zhao <yuzhao@xxxxxxxxxx> writes:
> +
> +#ifdef CONFIG_MEMCG
> +		if (memcg && atomic_read(&memcg->moving_account))
> +			goto contended;
> +#endif
> +		if (!mmap_read_trylock(mm))
> +			goto contended;

These are essentially spinloops. Surely you need a cpu_relax() somewhere?

In general for all of spinloop like constructs it would be useful to
consider how to teach lockdep about them.

> +	do {
> +		old_flags = READ_ONCE(page->flags);
> +		new_gen = ((old_flags & LRU_GEN_MASK) >> LRU_GEN_PGOFF) - 1;
> +		VM_BUG_ON_PAGE(new_gen < 0, page);
> +		if (new_gen >= 0 && new_gen != old_gen)
> +			goto sort;
> +
> +		new_gen = (old_gen + 1) % MAX_NR_GENS;
> +		new_flags = (old_flags & ~LRU_GEN_MASK) | ((new_gen + 1UL) << LRU_GEN_PGOFF);
> +		/* mark page for reclaim if pending writeback */
> +		if (front)
> +			new_flags |= BIT(PG_reclaim);
> +	} while (cmpxchg(&page->flags, old_flags, new_flags) !=
> old_flags);

I see this cmpxchg flags pattern a lot. Could there be some common code
factoring?

-Andi