linux-kernel - Re: [PATCH 04/15] mm: remove the pgmap field from struct hmm_vma

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Message-ID: <20190816123412.GB22140@lst.de>
Date:   Fri, 16 Aug 2019 14:34:12 +0200
From:   Christoph Hellwig <hch@....de>
To:     Jason Gunthorpe <jgg@...lanox.com>
Cc:     Christoph Hellwig <hch@....de>, Jerome Glisse <jglisse@...hat.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Ben Skeggs <bskeggs@...hat.com>,
        Felix Kuehling <Felix.Kuehling@....com>,
        Ralph Campbell <rcampbell@...dia.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "nouveau@...ts.freedesktop.org" <nouveau@...ts.freedesktop.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "amd-gfx@...ts.freedesktop.org" <amd-gfx@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 04/15] mm: remove the pgmap field from struct
 hmm_vma_walk

On Fri, Aug 16, 2019 at 12:30:41PM +0000, Jason Gunthorpe wrote:
> 
> For instance, a system may have multiple DEVICE_PRIVATE map's owned by
> the same driver - but multiple physical devices using that driver.
> 
> Each physical device's driver should only ever get DEVICE_PRIVATE
> pages for it's own on-device memory. Never a DEVICE_PRIVATE for
> another device's memory.
> 
> The dev_pagemap_ops would not be unique enough, right?

True.

> 
> Probably also clusters of same-driver struct device can share a
> DEVICE_PRIVATE, at least high end GPU's now have private memory
> coherency busses between their devices.
> 
> Since we want to trigger migration to CPU on incompatible
> DEVICE_PRIVATE pages, it seems best to sort this out in the
> hmm_range_fault?
> 
> Maybe some sort of unique ID inside the page->pgmap and passed as
> input?

Yes, we'll probably need an owner field.  And it's not just
hmm_range_fault, the migrate_vma_* routines as affected in the same
way.