netdev - Re: [PATCH v3 net-next 3/5] net: introduce common dev_page_is

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Date:   Sun, 31 Jan 2021 12:22:05 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Alexander Lobakin <alobakin@...me>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        John Hubbard <jhubbard@...dia.com>,
        David Rientjes <rientjes@...gle.com>,
        Yisen Zhuang <yisen.zhuang@...wei.com>,
        Salil Mehta <salil.mehta@...wei.com>,
        Jesse Brandeburg <jesse.brandeburg@...el.com>,
        Tony Nguyen <anthony.l.nguyen@...el.com>,
        Saeed Mahameed <saeedm@...dia.com>,
        Leon Romanovsky <leon@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        Willem de Bruijn <willemb@...gle.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Dexuan Cui <decui@...rosoft.com>,
        Jakub Sitnicki <jakub@...udflare.com>,
        Marco Elver <elver@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, intel-wired-lan@...ts.osuosl.org,
        linux-rdma@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v3 net-next 3/5] net: introduce common
 dev_page_is_reusable()

On Sun, Jan 31, 2021 at 12:11:52PM +0000, Alexander Lobakin wrote:
> A bunch of drivers test the page before reusing/recycling for two
> common conditions:
>  - if a page was allocated under memory pressure (pfmemalloc page);
>  - if a page was allocated at a distant memory node (to exclude
>    slowdowns).
> 
> Introduce a new common inline for doing this, with likely() already
> folded inside to make driver code a bit simpler.

I don't see the need for the 'dev_' prefix.  That actually confuses me
because it makes me think this is tied to ZONE_DEVICE or some such.

So how about calling it just 'page_is_reusable' and putting it in mm.h
with page_is_pfmemalloc() and making the comment a little less network-centric?

Or call it something like skb_page_is_recyclable() since it's only used
by networking today.  But I bet it could/should be used more widely.

> +/**
> + * dev_page_is_reusable - check whether a page can be reused for network Rx
> + * @page: the page to test
> + *
> + * A page shouldn't be considered for reusing/recycling if it was allocated
> + * under memory pressure or at a distant memory node.
> + *
> + * Returns false if this page should be returned to page allocator, true
> + * otherwise.
> + */
> +static inline bool dev_page_is_reusable(const struct page *page)
> +{
> +	return likely(page_to_nid(page) == numa_mem_id() &&
> +		      !page_is_pfmemalloc(page));
> +}
> +