Subject: Re: [PATCH net-next v8 07/17] net: page_pool: introduce page_pool_mp_return_in_cache

From: Jakub Kicinski <[email-masked]>
Date: Mon, 9 Dec 2024 19:40:57 -0800

On Wed,  4 Dec 2024 09:21:46 -0800 David Wei wrote:
> +/*
> + * page_pool_mp_return_in_cache() - return a netmem to the allocation cache.
> + * @pool:	pool from which pages were allocated
> + * @netmem:	netmem to return
> + *
> + * Return already allocated and accounted netmem to the page pool's allocation
> + * cache. The function doesn't provide synchronisation and must only be called
> + * from the napi context.

NAPI is irrelevant, this helper, IIUC, has to be called down the call
chain from mp_ops->alloc().

> + */
> +void page_pool_mp_return_in_cache(struct page_pool *pool, netmem_ref netmem)
> +{
> +	if (WARN_ON_ONCE(pool->alloc.count >= PP_ALLOC_CACHE_REFILL))
> +		return;

I'd

	return false;

without a warning.

> +	page_pool_dma_sync_for_device(pool, netmem, -1);
> +	page_pool_fragment_netmem(netmem, 1);
> +	pool->alloc.cache[pool->alloc.count++] = netmem;

and here:

	return true;

this say mps can use return value as a stop condition in a do {} while()
loop, without having to duplicate the check.

	do {
		netmem = alloc...
		... logic;
	} while (page_pool_mp_alloc_refill(pp, netmem));

	/* last netmem didn't fit in the cache */
	return netmem;