netdev - Re: [Lsf-pc] [LSF/MM/BPF proposal]: Physr discussion

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Date:   Mon, 23 Jan 2023 20:11:34 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     Jason Gunthorpe via Lsf-pc <lsf-pc@...ts.linux-foundation.org>,
        lsf-pc@...ts.linuxfoundation.org, linux-mm@...ck.org,
        iommu@...ts.linux.dev, linux-rdma@...r.kernel.org,
        nvdimm@...ts.linux.dev, John Hubbard <jhubbard@...dia.com>,
        Ming Lei <ming.lei@...hat.com>, linux-block@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, netdev@...r.kernel.org,
        Joao Martins <joao.m.martins@...cle.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        Christoph Hellwig <hch@....de>
Subject: Re: [Lsf-pc] [LSF/MM/BPF proposal]: Physr discussion

On Mon, Jan 23, 2023 at 11:36:51AM -0800, Dan Williams wrote:
> Jason Gunthorpe via Lsf-pc wrote:
> > I would like to have a session at LSF to talk about Matthew's
> > physr discussion starter:
> > 
> >  https://lore.kernel.org/linux-mm/YdyKWeU0HTv8m7wD@casper.infradead.org/
> > 
> > I have become interested in this with some immediacy because of
> > IOMMUFD and this other discussion with Christoph:
> > 
> >  https://lore.kernel.org/kvm/4-v2-472615b3877e+28f7-vfio_dma_buf_jgg@nvidia.com/
> 
> I think this is a worthwhile discussion. My main hangup with 'struct
> page' elimination in general is that if anything needs to be allocated

You're the first one to bring up struct page elimination.  Neither Jason
nor I have that as our motivation.  But there are reasons why struct page
is a bad data structure, and Xen proves that you don't need to have such
a data structure in order to do I/O.

> When I read "general interest across all the driver subsystems" it is
> hard not to ask "have all possible avenues to enable 'struct page' been
> exhausted?"

Yes, we should definitely expend yet more resources chasing a poor
implementation.