Messages in this thread | | | Date | Tue, 27 May 2008 01:47:20 -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 Tue, 27 May 2008 01:49:47 +0200 Miquel van Smoorenburg <mikevs@xs4all.net> wrote:
> Please consider the below patch for 2.6.26 (can somebody from the > x86 team pick this up please? Thank you) > > > > [PATCH] 2.6.26-rc: x86: pci-dma.c: use __GFP_NO_OOM instead of __GFP_NORETRY > > arch/x86/kernel/pci-dma.c::dma_alloc_coherent() adds __GFP_NORETRY to > the gfp flags before calling alloc_pages() to prevent the oom killer > from running.
Now, why does dma_alloc_coherent() do that?
If __GFP_FS is cleared (most cases) then we won't be calling out_of_memory() anyway.
If __GFP_FS _is_ set then setting __GFP_NORETRY will do much more than avoiding oom-killings. It will prevent the page allocator from retrying and will cause the problems which one assumes (without evidence :() you have observed.
So... why not just remove the setting of __GFP_NORETRY? Why is it wrong to oom-kill things in this case?
> This has the expected side effect that that alloc_pages() doesn't > retry anymore. Not really a problem for dma_alloc_coherent(.. GFP_ATOMIC) > which is the way most drivers use it (through pci_alloc_consistent()) > but drivers that call dma_alloc_coherent(.. GFP_KERNEL) directly can get > unexpected failures. > > Until we have the mask allocator, use a new flag __GFP_NO_OOM > instead of __GFP_NORETRY. >
But this change increases the chances of a caller getting stuck in the page allocator for ever, unable to make progress?
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