On Tue, Nov 25, 2014 at 02:44:33PM +0000, Chris Wilson wrote: > On Tue, Nov 25, 2014 at 02:30:55PM +0000, Daniel, Thomas wrote: > > > -----Original Message----- > > > From: daniel.vetter@xxxxxxxx [mailto:daniel.vetter@xxxxxxxx] On Behalf Of > > > Daniel Vetter > > > Sent: Thursday, November 20, 2014 12:51 PM > > > To: Chris Wilson; Daniel, Thomas; intel-gfx@xxxxxxxxxxxxxxxxxxxxx; akash goel > > > (akash.goels@xxxxxxxxx) > > > Subject: Re: [PATCH] drm/i915: Don't pin LRC in GGTT when > > > dumping in debugfs > > > > > > On Thu, Nov 20, 2014 at 1:28 PM, Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> > > > wrote: > > > >> Can you identify any situation where the pages may go away? > > > > > > > > Anytime you trigger an allocation, the system may reap any objects > > > > pages. It will even steal the dev->struct_mutex. To protect against > > > > the shrinker you have to call pin_pages(). Here, there are no > > > > allocations inside the loop and so you don't need to worry about the > > > > shrinker stealing your pages. > > > > > > Hm actually I think better safe than sorry here. At least I have > > > (again) completely forgotten about our dear shrinker ... > > > -Daniel > > > > Does this discussion count as a review? What was the conclusion - do I need to make a version without pinning or is it better safe than sorry? > > To bring it full circle: > > >> LRC object does not need to be mapped into the GGTT when dumping. Just use > >> pin_pages. A side-effect of this patch is that a compiler warning goes away > >> (not checking return value of i915_gem_obj_ggtt_pin). > > > Please explain why you need to pin the pages. > > In particular, explain why just calling pin_pages() doesn't do what you > want. And then afterwards you can leave a note in the commitlog why you > use pin_pages() as overkill. Ok I think I see the confusion - we still don't have any error checking, because we don't call get_pages. pin_pages alone doesn't do a whole lot really. We might actually want to put the get_pages into the pin_pages to simplify the interface a bit. Well we need to keep the raw version as __ since some users really don't want a get_pages. -Daniel -- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/intel-gfx
