linux-kernel - Re: [rfc 6/6] dma-remap: double the default DMA coherent pool size

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Date:   Thu, 5 Mar 2020 16:45:20 +0100
From:   Christoph Hellwig <hch@....de>
To:     David Rientjes <rientjes@...gle.com>
Cc:     Christoph Hellwig <hch@....de>,
        Tom Lendacky <thomas.lendacky@....com>,
        "Singh, Brijesh" <brijesh.singh@....com>,
        "Grimm, Jon" <jon.grimm@....com>, Joerg Roedel <joro@...tes.org>,
        baekhw@...gle.com,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>
Subject: Re: [rfc 6/6] dma-remap: double the default DMA coherent pool size

On Sun, Mar 01, 2020 at 04:05:27PM -0800, David Rientjes wrote:
> When AMD memory encryption is enabled, some devices may used more than
> 256KB/sec from the atomic pools.  Double the default size to make the
> original size and expansion more appropriate.
> 
> This provides a slight optimization on initial expansion and is deemed
> appropriate for all configs with CONFIG_DMA_REMAP enabled because of the
> increased reliance on the atomic pools.
> 
> Alternatively, this could be done only when CONFIG_AMD_MEM_ENCRYPT is
> enabled.

Can we just scale the initial size based on the system memory size?