Re: [PATCH] mm: add maybe_lru_add_drain() that only drains when threshold is exceeded

[Shakeel Butt <shakeel.butt@linux.dev>]

On Wed, Dec 18, 2024 at 11:56:04AM -0500, Rik van Riel wrote:
[...]
>  
> +static bool should_lru_add_drain(void)
> +{
> +	struct cpu_fbatches *fbatches = this_cpu_ptr(&cpu_fbatches);

You will need either a local_lock or preempt_disable to access the per
cpu batches.

> +	int pending = folio_batch_count(&fbatches->lru_add);
> +	pending += folio_batch_count(&fbatches->lru_deactivate);
> +	pending += folio_batch_count(&fbatches->lru_deactivate_file);
> +	pending += folio_batch_count(&fbatches->lru_lazyfree);
> +
> +	/* Don't bother draining unless we have several pages pending. */
> +	return pending > SWAP_CLUSTER_MAX;
> +}
> +
> +void maybe_lru_add_drain(void)

Later it might also make sense to see if other users of lru_add_drain()
should be fine with maybe_lru_add_drain() as well.

> +{
> +	if (should_lru_add_drain())
> +		lru_add_drain();
> +}
> +