netdev - Re: [PATCH v2 net-next 3/4] net: introduce common dev_page_is

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Date:   Sat, 30 Jan 2021 19:45:29 +0000
From:   Alexander Lobakin <alobakin@...me>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Alexander Lobakin <alobakin@...me>,
        "David S. Miller" <davem@...emloft.net>,
        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 v2 net-next 3/4] net: introduce common dev_page_is_reserved()

From: Jakub Kicinski <kuba@...nel.org>
Date: Sat, 30 Jan 2021 11:07:07 -0800

> On Sat, 30 Jan 2021 15:42:29 +0000 Alexander Lobakin wrote:
> > > On Wed, 27 Jan 2021 20:11:23 +0000 Alexander Lobakin wrote:
> > > > + * dev_page_is_reserved - 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 true if this page should be returned to page allocator, false
> > > > + * otherwise.
> > > > + */
> > > > +static inline bool dev_page_is_reserved(const struct page *page)
> > >
> > > Am I the only one who feels like "reusable" is a better term than
> > > "reserved".
> >
> > I thought about it, but this will need to inverse the conditions in
> > most of the drivers. I decided to keep it as it is.
> > I can redo if "reusable" is preferred.
> 
> Naming is hard. As long as the condition is not a double negative it
> reads fine to me, but that's probably personal preference.
> The thing that doesn't sit well is the fact that there is nothing
> "reserved" about a page from another NUMA node.. But again, if nobody
> +1s this it's whatever...

Agree on NUMA and naming. I'm a bit surprised that 95% of drivers
have this helper called "reserved" (one of the reasons why I finished
with this variant).
Let's say, if anybody else will vote for "reusable", I'll pick it for
v3.

> That said can we move the likely()/unlikely() into the helper itself?
> People on the internet may say otherwise but according to my tests
> using __builtin_expect() on a return value of a static inline helper
> works just fine.

Sounds fine, this will make code more elegant. Will publish v3 soon.

Thanks,
Al