On Sat, Mar 19, 2005 at 08:26:45PM +0100, Andi Kleen wrote:
> On Fri, Mar 18, 2005 at 03:23:44PM -0600, Matt Domsch wrote:
> > For review and comment.
> > 
> > On x86_64 systems with no IOMMU and with >4GB RAM (in fact, whenever
> > there are any pages mapped above 4GB), pci_alloc_consistent() falls
> > back to using ZONE_DMA for all allocations, even if the device's
> > dma_mask could have supported using memory from other zones.  Problems
> > can be seen when other ZONE_DMA users (SWIOTLB, scsi_malloc()) consume
> > all of ZONE_DMA, leaving none left for pci_alloc_consistent() use.
> > 
> > Patch below makes pci_alloc_consistent() for the nommu case (EM64T
> > processors) match the 2.6 implementation of dma_alloc_coherent(), with
> > the exception that this continues to use GFP_ATOMIC.
> 
> You fixed the wrong code. The pci-nommu code is only used
> when IOMMU is disabled in the Kconfig. But most kernels have
> it enabled. You would need to change it in pci-gart.c too.

OK, then how's this for review?  Compiles clean, can't test it myself
for a few days.

-- 
Matt Domsch
Software Architect
Dell Linux Solutions linux.dell.com & www.dell.com/linux
Linux on Dell mailing lists @ http://lists.us.dell.com

===== arch/x86_64/kernel/pci-gart.c 1.12 vs edited =====
--- 1.12/arch/x86_64/kernel/pci-gart.c  2004-06-03 05:29:36 -05:00
+++ edited/arch/x86_64/kernel/pci-gart.c        2005-03-19 15:56:34 -06:00
@@ -154,27 +154,37 @@ void *pci_alloc_consistent(struct pci_de
        int gfp = GFP_ATOMIC;
        int i;
        unsigned long iommu_page;
+       dma_addr_t dma_mask;
 
-       if (hwdev == NULL || hwdev->dma_mask < 0xffffffff || no_iommu)
+       if (hwdev == NULL || hwdev->dma_mask < 0xffffffff)
                gfp |= GFP_DMA;
 
+       dma_mask = hwdev ? hwdev->dma_mask : 0xffffffffULL;
+       if (dma_mask == 0)
+               dma_mask = 0xffffffffULL;
+
        /* 
-        * First try to allocate continuous and use directly if already 
-        * in lowmem. 
+        * First try to allocate continuous and use directly if
+        * our device supports it
         */ 
        size = round_up(size, PAGE_SIZE); 
+ again:
        memory = (void *)__get_free_pages(gfp, get_order(size));
        if (memory == NULL) {
                return NULL; 
        } else {
-               int high = 0, mmu;
-               if (((unsigned long)virt_to_bus(memory) + size) > 0xffffffffUL)
-                       high = 1;
-               mmu = high;
+               int high = (((unsigned long)virt_to_bus(memory) + size) & 
~dma_mask) != 0;
+               int mmu = high;
                if (force_mmu && !(gfp & GFP_DMA)) 
                        mmu = 1;
                if (no_iommu) { 
-                       if (high) goto error;
+                       if (high && (gfp & GFP_DMA))
+                               goto error;
+                       if (high) {
+                               free_pages((unsigned long)memory, 
get_order(size));
+                               gfp |= GFP_DMA;
+                               goto again;
+                       }
                        mmu = 0; 
                }       
                memset(memory, 0, size); 
-
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