Quoting Kirill A. Shutemov (2020-02-03 15:18:44) > On Fri, Jan 31, 2020 at 03:24:12PM +0000, Chris Wilson wrote: > > Quoting Kirill A. Shutemov (2015-03-19 17:08:15) > > > As far as I can see there's no users of PG_reserved on compound pages. > > > Let's use NO_COMPOUND here. > > > > Much later than you would ever expect, but we just had a user update an > > ancient device and trip over this. > > https://gitlab.freedesktop.org/drm/intel/issues/1027 > > > > In drm_pci_alloc() we allocate a high-order page (for it to be physically > > contiguous) and mark each page as Reserved. > > > > dmah->vaddr = dma_alloc_coherent(&dev->pdev->dev, size, > > &dmah->busaddr, > > GFP_KERNEL | __GFP_COMP); > > > > /* XXX - Is virt_to_page() legal for consistent mem? */ > > /* Reserve */ > > for (addr = (unsigned long)dmah->vaddr, sz = size; > > sz > 0; addr += PAGE_SIZE, sz -= PAGE_SIZE) { > > SetPageReserved(virt_to_page((void *)addr)); > > } > > > > It's been doing that since > > > > commit ddf19b973be5a96d77c8467f657fe5bd7d126e0f > > Author: Dave Airlie <airlied@xxxxxxxx> > > Date: Sun Mar 19 18:56:12 2006 +1100 > > > > drm: fixup PCI DMA support > > > > I haven't found anything to say if we are meant to be reserving the > > pages or not. So I bring it to your attention, asking for help. > > I don't see a real reason for these pages to be reserved. But I might be > wrong here. > > I tried to look around: other users (infiniband/ethernet) of > dma_alloc_coherent(__GFP_COMP) don't mess with PG_reserved. > > Could you try to drop it from DRM? That is the current plan. So long as there is nothing magical about either the __GFP_COMP or SetPageReserved, we should be able to drop them without any functional change. Only 2 very old bits of HW (r128, ancient i915) depend on this routine, and i915 seems, touch wood, quite happy with a plain dma_alloc_coherent(). -Chris
