Messages in this thread | | | Date | Wed, 28 May 2008 01:40:17 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH] 2.6.26-rc: x86: pci-dma.c: use __GFP_NO_OOM instead of __GFP_NORETRY |
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On Wed, 28 May 2008 10:31:25 +0200 Miquel van Smoorenburg <mikevs@xs4all.net> wrote:
> > 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;
I guess that's more specifally solving that-which-we-wish-to-solve.
Formally we should be testing __GFP_DMA here, not GFP_DMA - just the zone selector field. They're presently equal, but someone could legitimately come along and do
#define GFP_DMA (__GFP_DMA|__GFP_HIGH)
or similar.
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