netdev - Re: [RFC PATCH v2 11/21] core/skbuff: add page recycling logic for netgpu pages

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Message-ID: <20200728180040.az3xgwzmuz6grv32@bsd-mbp.dhcp.thefacebook.com>
Date:   Tue, 28 Jul 2020 11:00:40 -0700
From:   Jonathan Lemon <jonathan.lemon@...il.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     netdev@...r.kernel.org, kernel-team@...com
Subject: Re: [RFC PATCH v2 11/21] core/skbuff: add page recycling logic for
 netgpu pages

On Tue, Jul 28, 2020 at 06:28:25PM +0200, Greg KH wrote:
> On Mon, Jul 27, 2020 at 03:44:34PM -0700, Jonathan Lemon wrote:
> > From: Jonathan Lemon <bsd@...com>
> > 
> > netgpu pages will always have a refcount of at least one (held by
> > the netgpu module).  If the skb is marked as containing netgpu ZC
> > pages, recycle them back to netgpu.
> 
> What???

Yes, this is page refcount elevation.  ZONE_DEVICE pages do this also,
which is hidden in put_devmap_managed_page().  I would really like to
find a generic solution for this, as it has come up in other cases as
well (page recycling for page_pool, for example).  Some way to say "this
page is different", and a separate routine to release refcounts.

Can we have a discussion on this possibility?
-- 
Jonathan