Re: [RFC 0/4] RFC - Coherent Device Memory (Not for inclusion)

[Balbir Singh <bsingharora@gmail.com>]

On Thu, 2017-05-04 at 10:33 -0700, Dave Hansen wrote:
> On 05/04/2017 08:49 AM, Benjamin Herrenschmidt wrote:
> > On Thu, 2017-05-04 at 14:52 +0200, Michal Hocko wrote:
> > > But the direct reclaim would be effective only _after_ all other nodes
> > > are full.
> > > 
> > > I thought that kswapd reclaim is a problem because the HW doesn't
> > > support aging properly but as the direct reclaim works then what is the
> > > actual problem?
> > 
> > Ageing isn't isn't completely broken. The ATS MMU supports
> > dirty/accessed just fine.
> > 
> > However the TLB invalidations are quite expensive with a GPU so too
> > much harvesting is detrimental, and the GPU tends to check pages out
> > using a special "read with intend to write" mode, which means it almost
> > always set the dirty bit if the page is writable to begin with.
> 
> Why do you have to invalidate the TLB?  Does the GPU have a TLB so large
> that it can keep thing in the TLB for super-long periods of time?
> 
> We don't flush the TLB on clearing Accessed on x86 normally.

Isn't that mostly because x86 relies on non-global pages to be flushed
on context switch?

Balbir Singh.

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>