Re: [Xen-devel] [PATCH v2 1/2] Resize the MAX_NR_IO_RANGES for ioreq server

[George Dunlap <dunlapg@xxxxxxxxx>]

On Mon, Jul 6, 2015 at 7:25 AM, Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx> wrote:
> MAX_NR_IO_RANGES is used by ioreq server as the maximum
> number of discrete ranges to be tracked. This patch changes
> its value to 8k, so that more ranges can be tracked on next
> generation of Intel platforms in XenGT. Future patches can
> extend the limit to be toolstack tunable, and MAX_NR_IO_RANGES
> can serve as a default limit.
>
> Signed-off-by: Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx>

I said this at the Hackathon, and I'll say it here:  I think this is
the wrong approach.

The problem here is not that you don't have enough memory ranges.  The
problem is that you are not tracking memory ranges, but individual
pages.

You need to make a new interface that allows you to tag individual
gfns as p2m_mmio_write_dm, and then allow one ioreq server to get
notifications for all such writes.

 -George

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