> -----Original Message----- > From: Chris Wilson [mailto:chris@xxxxxxxxxxxxxxxxxx] > Sent: Monday, March 09, 2015 8:02 PM > To: Zou, Nanhai > Cc: Daniel Vetter; Song, Ruiling; Vetter, Daniel; intel-gfx@xxxxxxxxxxxxxxxxxxxxx; > Yang, Rong R; beignet@xxxxxxxxxxxxxxxxxxxxx; Weinehall, David > Subject: Re: [Beignet] Preventing zero GPU virtual address allocation > > On Mon, Mar 09, 2015 at 02:34:46AM +0000, Zou, Nanhai wrote: > > We don't need MAP_FIXED, we just want to avoid address 0 to be allocated. > > > > Though I think using MAP_FIXED is overkill, will bring much unnecessary > complexity on both kernel and beignet side. > > I don't mind if people can provide stable MAP_FIXED patches to resolve this > problem a few months or years later. > > > > At that time, kernel driver can revert the reserve page 0 patch. > > Before that reserve page 0 can benefit all the Beignet user without breaking > anything. > > The point is that is becomes ABI. So no the kernel can't just revert it. > There is nothing special about address 0 in ether GTT or virtual memory. > If you require a special object allocated at address 0, allocate a special object > at address 0. > -Chris Hi, Zero page is not an ABI, It is only a strategy of virtual space allocation. Nobody would need exactly a page of virtual address 0. So there is no dependency. Zero page is a very common used method to avoid the NULL pointer issue. See http://en.wikipedia.org/wiki/Zero_page I can see a lot of issue to do that with MAP_FIXED zero page in user space. Say if a program combine libva, beignet and mesa or other graphics components together, which component should be responsible of allocating this zero page? What if a component happened to allocate a page in offset 0 before beignet and release it later? Using a zero page just remove the unnecessary mess and resolve problem in a clean explicit way. Thanks Zou Nanhai > -- > Chris Wilson, Intel Open Source Technology Centre _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/intel-gfx
