netdev - Re: [RFC PATCH V4 01/13] netback: page pool version 1

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Message-ID: <1329755163.2203.352.camel@leeds.uk.xensource.com>
Date:	Mon, 20 Feb 2012 16:26:03 +0000
From:	Wei Liu <wei.liu2@...rix.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	<wei.liu2@...rix.com>, Eric Dumazet <eric.dumazet@...il.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"Ian Campbell" <Ian.Campbell@...rix.com>
Subject: Re: [RFC PATCH V4 01/13] netback: page pool version 1

On Fri, 2012-02-17 at 19:19 +0000, Konrad Rzeszutek Wilk wrote:
> > 
> > Hmm, this kind of stuff should be discussed on lkml.
> > 
> > I doubt we want yet another memory allocator, with a global lock
> > (contended), and no NUMA properties.
> 
> That should be fixed. Are there any existing memory pools that could be used
> instead? I (And I think everybody) is all for using the existing APIs if  they
> can do the job. I was lookign a bit at the dmapool code, but that requires something
> we don't have  - the 'struct device'. We could manufacture a fake one, but that just
> stinks of hack.
> 

I've been thinking about this for a long time, so any recommendation is
welcomed.

It is not my intention to write yet another memory allocator. What I
need is a data structure to track pages owned by netback.

Let me state the requirements of this data structure:
     1. limits overall memory used by all vifs (this could also be met
        by the underlying allocator)
     2. provides function to tell whether a particular page is mapped
        from foreign domain -- is_in_pool() is a surrogate for that
     3. provides function to back-reference owner vif of the page

To achieve requirement 2, page pool manipulates page->mapping field. To
achieve requirement 3, page pool maintains idx <-> vif relationship
internally.

I think I can use mempool internally for page allocation. But I still
need a data structure to meet other requirements.

> It [pagepool] also should use the shrinker API I think.

This is doable, but let's make everybody happy with the page pool design
and implementation first.


Wei.

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