Russell, On Fri, Jan 8, 2016 at 3:18 PM, Russell King - ARM Linux <linux@xxxxxxxxxxxxxxxx> wrote: > 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.) Ah, that makes so much more sense now! :) So you were suggesting something like DMA_ATTR_SMALL_PAGES_OK. Then you if we wanted all possible states you'd have 0 vs. DMA_ATTR_SMALL_PAGES_OK vs. DMA_ATTR_HUGE_PAGE? That would avoid the double-negative but does have the downside that it's less obvious that DMA_ATTR_SMALL_PAGES_OK is the opposite of DMA_ATTR_HUGE_PAGE. I think I still have a bit of a bias towards matching the MADV API, but I also am happy to change things if that's what people want. How about if I see other people chiming in saying that they'd prefer something like "DMA_ATTR_SMALL_PAGES_OK" then I'll change it, otherwise I'll leave it as-is (since you said you didn't have a strong opinion on it). -Doug -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
