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Re: [PATCH v4 2/3] common: DMA-mapping: add DMA_ATTR_NOHUGEPAGE attribute

From Russell King - ARM Linux <linux@arm.linux.org.uk>
Newsgroups linux.kernel
Subject Re: [PATCH v4 2/3] common: DMA-mapping: add DMA_ATTR_NOHUGEPAGE attribute
Date 2016-01-09 00:30 +0100
Message-ID <qOODM-5p4-7@gated-at.bofh.it> (permalink)
References <qOtfY-7iv-19@gated-at.bofh.it> <qOtfY-7iv-17@gated-at.bofh.it> <qOFqO-7nf-21@gated-at.bofh.it> <qOOkq-5fH-13@gated-at.bofh.it>
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On Fri, Jan 08, 2016 at 03:05:13PM -0800, Doug Anderson wrote:
> 1. I have to go and touch all existing DMA-mapping code to set
> DMA_ATTR_HUGE_PAGE.  That will be a big patchset and touch more code,
> making it more likely to break something.
...

Indeed, I was actually thinking of a positive "prefer/only use/force
smaller pages" thing rather than "allow huge pages" as a way to get
rid of the "no huge pages" negative as a way to get around that.
It has the same meaning when set as DMA_ATTR_NO_HUGE_PAGE but
avoids the problem of wondering what

	!dma_get_attr(DMA_ATTR_NO_HUGE_PAGE, attrs)

means.

I wasn't thinking of DMA_ATTR_HUGE_PAGE as that would certainly be
wrong when CONFIG_HAVE_DMA_ATTRS is disabled (when dma_get_attr()
always returns 0.)

-- 
RMK's Patch system: http://www.arm.linux.org.uk/developer/patches/
FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up
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[PATCH v4 2/3] common: DMA-mapping: add DMA_ATTR_NOHUGEPAGE attribute Douglas Anderson <dianders@chromium.org> - 2016-01-08 01:40 +0100
  Re: [PATCH v4 2/3] common: DMA-mapping: add DMA_ATTR_NOHUGEPAGE  attribute Robin Murphy <robin.murphy@arm.com> - 2016-01-08 14:20 +0100
    Re: [PATCH v4 2/3] common: DMA-mapping: add DMA_ATTR_NOHUGEPAGE attribute Doug Anderson <dianders@chromium.org> - 2016-01-09 00:10 +0100
  Re: [PATCH v4 2/3] common: DMA-mapping: add DMA_ATTR_NOHUGEPAGE  attribute Russell King - ARM Linux <linux@arm.linux.org.uk> - 2016-01-08 14:40 +0100
    Re: [PATCH v4 2/3] common: DMA-mapping: add DMA_ATTR_NOHUGEPAGE attribute Doug Anderson <dianders@chromium.org> - 2016-01-09 00:10 +0100
      Re: [PATCH v4 2/3] common: DMA-mapping: add DMA_ATTR_NOHUGEPAGE  attribute Russell King - ARM Linux <linux@arm.linux.org.uk> - 2016-01-09 00:30 +0100
        Re: [PATCH v4 2/3] common: DMA-mapping: add DMA_ATTR_NOHUGEPAGE attribute Doug Anderson <dianders@chromium.org> - 2016-01-09 00:40 +0100
          Re: [PATCH v4 2/3] common: DMA-mapping: add DMA_ATTR_NOHUGEPAGE  attribute Christoph Hellwig <hch@infradead.org> - 2016-01-09 09:00 +0100
            Re: [PATCH v4 2/3] common: DMA-mapping: add DMA_ATTR_NOHUGEPAGE attribute Tomasz Figa <tfiga@chromium.org> - 2016-01-09 17:30 +0100
  Re: [PATCH v4 2/3] common: DMA-mapping: add DMA_ATTR_NOHUGEPAGE  attribute Christoph Hellwig <hch@infradead.org> - 2016-01-08 14:50 +0100
    Re: [PATCH v4 2/3] common: DMA-mapping: add DMA_ATTR_NOHUGEPAGE attribute Doug Anderson <dianders@chromium.org> - 2016-01-09 00:10 +0100
      Re: [PATCH v4 2/3] common: DMA-mapping: add DMA_ATTR_NOHUGEPAGE  attribute Christoph Hellwig <hch@infradead.org> - 2016-01-09 09:00 +0100

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