linux-kernel - Re: drm/radeon spamming alloc_contig

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Date:   Thu, 1 Dec 2016 15:11:25 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     "Robin H. Johnson" <robbat2@...too.org>,
        Michal Nazarewicz <mina86@...a86.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        dri-devel@...ts.freedesktop.org, Joonsoo Kim <js1304@...il.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>
Subject: Re: drm/radeon spamming alloc_contig_range: [xxx, yyy) PFNs busy busy

Let's also CC Marek

On Thu 01-12-16 08:43:40, Vlastimil Babka wrote:
> On 12/01/2016 08:21 AM, Michal Hocko wrote:
> > Forgot to CC Joonsoo. The email thread starts more or less here
> > http://lkml.kernel.org/r/20161130092239.GD18437@dhcp22.suse.cz
> > 
> > On Thu 01-12-16 08:15:07, Michal Hocko wrote:
> > > On Wed 30-11-16 20:19:03, Robin H. Johnson wrote:
> > > [...]
> > > > alloc_contig_range: [83f2a3, 83f2a4) PFNs busy
> > > 
> > > Huh, do I get it right that the request was for a _single_ page? Why do
> > > we need CMA for that?
> 
> Ugh, good point. I assumed that was just the PFNs that it failed to migrate
> away, but it seems that's indeed the whole requested range. Yeah sounds some
> part of the dma-cma chain could be smarter and attempt CMA only for e.g.
> costly orders.

Is there any reason why the DMA api doesn't try the page allocator first
before falling back to the CMA? I simply have a hard time to see why the
CMA should be used (and fragment) for small requests size.
-- 
Michal Hocko
SUSE Labs