netdev - Re: [RFC Patch v1 1/3] net: ena: implement local page cache (LPC) system

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Date:   Tue, 9 Mar 2021 18:57:06 +0100
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Shay Agroskin <shayagr@...zon.com>,
        David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org
Cc:     "Woodhouse, David" <dwmw@...zon.com>,
        "Machulsky, Zorik" <zorik@...zon.com>,
        "Matushevsky, Alexander" <matua@...zon.com>,
        Saeed Bshara <saeedb@...zon.com>,
        "Wilson, Matt" <msw@...zon.com>,
        "Liguori, Anthony" <aliguori@...zon.com>,
        "Bshara, Nafea" <nafea@...zon.com>,
        "Tzalik, Guy" <gtzalik@...zon.com>,
        "Belgazal, Netanel" <netanel@...zon.com>,
        "Saidi, Ali" <alisaidi@...zon.com>,
        "Herrenschmidt, Benjamin" <benh@...zon.com>,
        "Kiyanovski, Arthur" <akiyano@...zon.com>,
        "Jubran, Samih" <sameehj@...zon.com>,
        "Dagan, Noam" <ndagan@...zon.com>
Subject: Re: [RFC Patch v1 1/3] net: ena: implement local page cache (LPC)
 system



On 3/9/21 6:10 PM, Shay Agroskin wrote:
> The page cache holds pages we allocated in the past during napi cycle,
> and tracks their availability status using page ref count.
> 
> The cache can hold up to 2048 pages. Upon allocating a page, we check
> whether the next entry in the cache contains an unused page, and if so
> fetch it. If the next page is already used by another entity or if it
> belongs to a different NUMA core than the napi routine, we allocate a
> page in the regular way (page from a different NUMA core is replaced by
> the newly allocated page).
> 
> This system can help us reduce the contention between different cores
> when allocating page since every cache is unique to a queue.

For reference, many drivers already use a similar strategy.

> +
> +/* Fetch the cached page (mark the page as used and pass it to the caller).
> + * If the page belongs to a different NUMA than the current one, free the cache
> + * page and allocate another one instead.
> + */
> +static struct page *ena_fetch_cache_page(struct ena_ring *rx_ring,
> +					 struct ena_page *ena_page,
> +					 dma_addr_t *dma,
> +					 int current_nid)
> +{
> +	/* Remove pages belonging to different node than current_nid from cache */
> +	if (unlikely(page_to_nid(ena_page->page) != current_nid)) {
> +		ena_increase_stat(&rx_ring->rx_stats.lpc_wrong_numa, 1, &rx_ring->syncp);
> +		ena_replace_cache_page(rx_ring, ena_page);
> +	}
> +
> 

And they use dev_page_is_reusable() instead of copy/pasting this logic.

As a bonus, they properly deal with pfmemalloc