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

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Message-ID: <20210131125713.8710-1-alobakin@pm.me>
Date:   Sun, 31 Jan 2021 12:57:29 +0000
From:   Alexander Lobakin <alobakin@...me>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Alexander Lobakin <alobakin@...me>,
        "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()

From: Matthew Wilcox <willy@...radead.org>
Date: Sun, 31 Jan 2021 12:22:05 +0000

> 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.

Several functions right above this one also use 'dev_' prefix. It's
a rather old mark that it's about network devices.

> 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?

This pair of conditions (!pfmemalloc + local memory node) is really
specific to network drivers. I didn't see any other instances of such
tests, so I don't see a reason to place it in a more common mm.h.

> 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.

There's nothing about skb. Tested page is just a memory chunk for DMA
transaction. It can be used as skb head/frag, for XDP buffer/frame or
for XSK umem.

> > +/**
> > + * 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));
> > +}
> > +

Al