lkml.org 
[lkml]   [2016]   [Jan]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [PATCH v4 2/3] common: DMA-mapping: add DMA_ATTR_NOHUGEPAGE attribute
From
Russell,

On Fri, Jan 8, 2016 at 3:18 PM, Russell King - ARM Linux
<linux@arm.linux.org.uk> 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

\
 
 \ /
  Last update: 2016-01-09 01:21    [W:0.095 / U:0.028 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site