Re: [PATCH 0/3] Fix kdump failures with crashkernel=high
From: WANG Chao
Date: Tue Dec 02 2014 - 23:01:53 EST
> here is a patch-set to fix failed kdump kernel boots when
> the systems was booted with crashkernel=X,high. On those
> systems the kernel allocates only 72MiB of low-memory for
> DMA buffers, which showed to be too low on some systems.
>From your experience It seems like swiotlb isn't working well with
crashkernel=X,high alone. What about using crashkernel=X,low with
crashkernel=X,high? Is there any reason you have to use
> The problem is that 64MiB of the low-memory is allocated by
> swiotlb, leaving 8MB for the page-allocator. But swiotlb
> tries to allocate DMA memory from the page-allocator first,
> which fails pretty fast in the boot sequence, causing
> warnings. This patch-set removes these warnings.
> But even the 64MiB for swiotlb are eaten up on some systems,
> so that the default of low-memory allocated for the
> crash-kernel is increase from 72MB to 256MB (only changing
> the defaults, can still be overwritten by crashkernel=X,low).
crashkernel=X,high shouldn't automatically reserve 72M low at the first
place. Now it's going insane if you increase it to 256M by default.
> This number comes from experiments on the affected systems,
> 128MiB low-memory was still not enough there, thus I set the
> value to 256MiB to fix the issues.
> Any feedback appreciated.
> Joerg Roedel (3):
> swiotlb: Warn on allocation failure in swiotlb_alloc_coherent
> x86, swiotlb: Try coherent allocations with __GFP_NOWARN
> x86, crash: Allocate enough low-mem when crashkernel=high
> arch/x86/kernel/pci-swiotlb.c | 8 ++++++++
> arch/x86/kernel/setup.c | 5 ++++-
> lib/swiotlb.c | 11 +++++++++--
> 3 files changed, 21 insertions(+), 3 deletions(-)
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