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SubjectRe: [PATCH] 2.6.26-rc: x86: pci-dma.c: use __GFP_NO_OOM instead of __GFP_NORETRY
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On Wed, 2008-05-28 at 04:47 +0200, Andi Kleen wrote:
> > So... why not just remove the setting of __GFP_NORETRY? Why is it
> > wrong to oom-kill things in this case?
>
> When the 16MB zone overflows (which can be common in some workloads)
> calling the OOM killer is pretty useless because it has barely any
> real user data [only exception would be the "only 16MB" case Alan
> mentioned]. Killing random processes in this case is bad.
>
> I think for 16MB __GFP_NORETRY is ok because there should be
> nothing freeable in there so looping is useless. Only exception would be the
> "only 16MB total" case again but I'm not sure 2.6 supports that at all
> on x86.
>
> On the other hand d_a_c() does more allocations than just 16MB, especially
> on 64bit and the other zones need different strategies.

Okay, so how about this then ?

--- linux-2.6.26-rc4.orig/arch/x86/kernel/pci-dma.c 2008-05-26 20:08:11.000000000 +0200
+++ linux-2.6.26-rc4/arch/x86/kernel/pci-dma.c 2008-05-28 10:27:41.000000000 +0200
@@ -397,9 +397,6 @@
if (dev->dma_mask == NULL)
return NULL;

- /* Don't invoke OOM killer */
- gfp |= __GFP_NORETRY;
-
#ifdef CONFIG_X86_64
/* Why <=? Even when the mask is smaller than 4GB it is often
larger than 16MB and in this case we have a chance of
@@ -410,7 +407,9 @@
#endif

again:
- page = dma_alloc_pages(dev, gfp, get_order(size));
+ /* Don't invoke OOM killer or retry in lower 16MB DMA zone */
+ page = dma_alloc_pages(dev,
+ (gfp & GFP_DMA) ? gfp | __GFP_NORETRY : gfp, get_order(size));
if (page == NULL)
return NULL;

Mike.



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