netdev - Re: [PATCH V2] net: ethernet: mellanox: correct page conversion

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Message-ID: <20160418131058.GA25421@infradead.org>
Date:	Mon, 18 Apr 2016 06:10:58 -0700
From:	Christoph Hellwig <hch@...radead.org>
To:	okaya@...eaurora.org
Cc:	Christoph Hellwig <hch@...radead.org>, linux-rdma@...r.kernel.org,
	timur@...eaurora.org, cov@...eaurora.org,
	Yishai Hadas <yishaih@...lanox.com>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2] net: ethernet: mellanox: correct page conversion

On Mon, Apr 18, 2016 at 09:06:18AM -0400, okaya@...eaurora.org wrote:
> On 2016-04-18 08:12, Christoph Hellwig wrote:
> >On Sat, Apr 16, 2016 at 06:23:32PM -0400, Sinan Kaya wrote:
> >>Current code is assuming that the address returned by dma_alloc_coherent
> >>is a logical address. This is not true on ARM/ARM64 systems.
> >
> >Can you explain what you mean with a 'logical address' and what actual
> >issue you're trying to solve?
> 
> Vmap call is failing on arm64 systems because dma alloc api already returns
> an address mapped with vmap.

Please state your problem clearly.  What I'm reverse engineering from
your posts is:  because dma_alloc_coherent uses vmap-like mappings on
arm64 (all, some systems?) a driver using a lot of them might run into
limits of the vmap pool size.

Is this correct?

> 
> Please see arch/arm64/mm directory.
---end quoted text---