On Thu, Nov 20, 2014 at 12:09:18PM +0000, Daniel, Thomas wrote: > > -----Original Message----- > > From: Chris Wilson [mailto:[email protected]] > > Sent: Thursday, November 20, 2014 11:41 AM > > To: Daniel, Thomas > > Cc: [email protected]; akash goel ([email protected]) > > Subject: Re: [Intel-gfx] [PATCH] drm/i915: Don't pin LRC in GGTT when > > dumping in debugfs > > > > On Thu, Nov 20, 2014 at 11:25:57AM +0000, Daniel, Thomas wrote: > > > > -----Original Message----- > > > > From: Chris Wilson [mailto:[email protected]] > > > > Sent: Thursday, November 20, 2014 11:16 AM > > > > To: Daniel, Thomas > > > > Cc: [email protected]; [email protected] > > > > Subject: Re: [Intel-gfx] [PATCH] drm/i915: Don't pin LRC in GGTT > > > > when dumping in debugfs > > > > > > > > On Thu, Nov 20, 2014 at 11:12:05AM +0000, Thomas Daniel wrote: > > > > > 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. > > > I suppose I don't as this is protected by the struct mutex and unpin is > > > called > > before returning. > > > > The question is: do we need protection against kmalloc and a potential call > > into the shrinker who may steal the pages from underneath us. Here, we > > only do a seq_printf() under the lock after get_pages() and that uses a > > preallocated buffer. > I don't think so... If a context is in the context_list then the ctx_obj will > have a nonzero refcount. The struct mutex prevents the refcount from > changing.
The shrinker only steals pages. Well it may reap the active reference count as well, which must also be kept in mind, but the ctx_obj should have the reference from being inside the list and be safe. > 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. -Chris -- Chris Wilson, Intel Open Source Technology Centre _______________________________________________ Intel-gfx mailing list [email protected] http://lists.freedesktop.org/mailman/listinfo/intel-gfx
