netdev - Re: [RFC PATCH v2 03/21] mm: Allow DMA mapping of pages which are not online

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Message-ID: <20200727170819.eix3n66gwb4izlq7@bsd-mbp.dhcp.thefacebook.com>
Date:   Mon, 27 Jul 2020 10:08:19 -0700
From:   Jonathan Lemon <jonathan.lemon@...il.com>
To:     Christoph Hellwig <hch@....de>
Cc:     netdev@...r.kernel.org, kernel-team@...com, robin.murphy@....com,
        akpm@...ux-foundation.org, davem@...emloft.net, kuba@...nel.org,
        willemb@...gle.com, edumazet@...gle.com,
        steffen.klassert@...unet.com, saeedm@...lanox.com,
        maximmi@...lanox.com, bjorn.topel@...el.com,
        magnus.karlsson@...el.com, borisp@...lanox.com, david@...hat.com
Subject: Re: [RFC PATCH v2 03/21] mm: Allow DMA mapping of pages which are
 not online

On Mon, Jul 27, 2020 at 07:58:13AM +0200, Christoph Hellwig wrote:
> On Sun, Jul 26, 2020 at 10:28:28PM -0700, Jonathan Lemon wrote:
> > Change the system RAM check from 'valid' to 'online', so dummy
> > pages which refer to external DMA resources can be mapped.
> 
> NAK.  This looks completely bogus.  Maybe you do have a good reason
> somewhere (although I doubt it), but then you'd actualy need to both
> explain it here, and also actually make sure I get the whole damn series.

The entire patchset was sent out in one command - I have no control over
how the mail server ends up delivering things.

An alternative here would just allocate 'struct pages' from normal
system memory, instead of from the system resources.  I initially did it
this way so the page could be used in the normal fashion to locate the
DMA address, instead of having a separate lookup table.
-- 
Jonathan