On 04/05/2013 06:16 AM, Yinghai Lu wrote:
> Chao said that kdump does does work well on his system on 3.8
> without extra parameter, even iommu does not work with kdump.
> And now have to append crashkernel_low=Y in first kernel to make
> kdump work.
>
> We have now modified crashkernel=X to allocate memory beyong 4G (if
> available) and do not allocate low range for crashkernel if the user
> does not specify that with crashkernel_low=Y. This causes regression
> if iommu is not enabled. Without iommu, swiotlb needs to be setup in
> first 4G and there is no low memory available to second kernel.
Is it possible to reuse the 1st kernel swiotlb region in 2nd capture
kernel if it's available?
>
> Set crashkernel_low automatically if the user does not specify that.
>
> For system that does support IOMMU with kdump properly, user could
> specify crashkernel_low=0 to save that 72M low ram.
How about make swiotlb size tunable in 1st kernel as well such as adding
a swiotlb_size= to cmdline, if it's set in 1st kernel crashkernel
reserving code can take it automaticlly.
This will benefit to user who use low-mem machines.
>
> -v3: add swiotlb_size() according to Konrad.
> -v4: add comments what 8M is for according to hpa.
> also update more crashkernel_low= in kernel-parameters.txt
> -v5: update changelog according to Vivek.
> -v6: Change description about swiotlb referring according to HATAYAMA.
>
> Reported-by: WANG Chao <chaow...@redhat.com>
> Tested-by: WANG Chao <chaow...@redhat.com>
> Signed-off-by: Yinghai Lu <ying...@kernel.org>
>
> ---
> Documentation/kernel-parameters.txt | 14 +++++++++++---
> arch/x86/kernel/setup.c | 20 +++++++++++++++++---
> include/linux/swiotlb.h | 1 +
> lib/swiotlb.c | 19 +++++++++++++++----
> 4 files changed, 44 insertions(+), 10 deletions(-)
>
> Index: linux-2.6/arch/x86/kernel/setup.c
> ===================================================================
> --- linux-2.6.orig/arch/x86/kernel/setup.c
> +++ linux-2.6/arch/x86/kernel/setup.c
> @@ -519,19 +519,33 @@ static void __init reserve_crashkernel_l
> unsigned long long low_base = 0, low_size = 0;
> unsigned long total_low_mem;
> unsigned long long base;
> + bool auto_set = false;
> int ret;
>
> total_low_mem = memblock_mem_size(1UL<<(32-PAGE_SHIFT));
> ret = parse_crashkernel_low(boot_command_line, total_low_mem,
> &low_size, &base);
> - if (ret != 0 || low_size <= 0)
> - return;
> + if (ret != 0) {
> + /*
> + * two parts from lib/swiotlb.c:
> + * swiotlb size: user specified with swiotlb= or default.
> + * swiotlb overflow buffer: now is hardcoded to 32k,
> + * round to 8M to cover more others.
> + */
> + low_size = swiotlb_size_or_default() + (8UL<<20);
> + auto_set = true;
> + } else {
> + /* passed with crashkernel_low=0 ? */
> + if (!low_size)
> + return;
> + }
>
> low_base = memblock_find_in_range(low_size, (1ULL<<32),
> low_size, alignment);
>
> if (!low_base) {
> - pr_info("crashkernel low reservation failed - No suitable area
> found.\n");
> + if (!auto_set)
> + pr_info("crashkernel low reservation failed - No
> suitable area found.\n");
>
> return;
> }
> Index: linux-2.6/include/linux/swiotlb.h
> ===================================================================
> --- linux-2.6.orig/include/linux/swiotlb.h
> +++ linux-2.6/include/linux/swiotlb.h
> @@ -25,6 +25,7 @@ extern int swiotlb_force;
> extern void swiotlb_init(int verbose);
> int swiotlb_init_with_tbl(char *tlb, unsigned long nslabs, int verbose);
> extern unsigned long swiotlb_nr_tbl(void);
> +unsigned long swiotlb_size_or_default(void);
> extern int swiotlb_late_init_with_tbl(char *tlb, unsigned long nslabs);
>
> /*
> Index: linux-2.6/lib/swiotlb.c
> ===================================================================
> --- linux-2.6.orig/lib/swiotlb.c
> +++ linux-2.6/lib/swiotlb.c
> @@ -105,9 +105,9 @@ setup_io_tlb_npages(char *str)
> if (!strcmp(str, "force"))
> swiotlb_force = 1;
>
> - return 1;
> + return 0;
> }
> -__setup("swiotlb=", setup_io_tlb_npages);
> +early_param("swiotlb", setup_io_tlb_npages);
> /* make io_tlb_overflow tunable too? */
>
> unsigned long swiotlb_nr_tbl(void)
> @@ -115,6 +115,18 @@ unsigned long swiotlb_nr_tbl(void)
> return io_tlb_nslabs;
> }
> EXPORT_SYMBOL_GPL(swiotlb_nr_tbl);
> +
> +/* default to 64MB */
> +#define IO_TLB_DEFAULT_SIZE (64UL<<20)
> +unsigned long swiotlb_size_or_default(void)
> +{
> + unsigned long size;
> +
> + size = io_tlb_nslabs << IO_TLB_SHIFT;
> +
> + return size ? size : (IO_TLB_DEFAULT_SIZE);
> +}
> +
> /* Note that this doesn't work with highmem page */
> static dma_addr_t swiotlb_virt_to_bus(struct device *hwdev,
> volatile void *address)
> @@ -188,8 +200,7 @@ int __init swiotlb_init_with_tbl(char *t
> void __init
> swiotlb_init(int verbose)
> {
> - /* default to 64MB */
> - size_t default_size = 64UL<<20;
> + size_t default_size = IO_TLB_DEFAULT_SIZE;
> unsigned char *vstart;
> unsigned long bytes;
>
> Index: linux-2.6/Documentation/kernel-parameters.txt
> ===================================================================
> --- linux-2.6.orig/Documentation/kernel-parameters.txt
> +++ linux-2.6/Documentation/kernel-parameters.txt
> @@ -596,9 +596,6 @@ bytes respectively. Such letter suffixes
> is selected automatically. Check
> Documentation/kdump/kdump.txt for further details.
>
> - crashkernel_low=size[KMG]
> - [KNL, x86] parts under 4G.
> -
> crashkernel=range1:size1[,range2:size2,...][@offset]
> [KNL] Same as above, but depends on the memory
> in the running system. The syntax of range is
> @@ -606,6 +603,17 @@ bytes respectively. Such letter suffixes
> a memory unit (amount[KMG]). See also
> Documentation/kdump/kdump.txt for an example.
>
> + crashkernel_low=size[KMG]
> + [KNL, x86_64] range under 4G. When crashkernel= is
> + passed, kernel allocate physical memory region
> + above 4G, that cause second kernel crash on system
> + that require some amount of low memory, e.g. swiotlb
> + requires at least 64M+32K low memory. Kernel would
> + try to allocate 72M below 4G automatically.
> + This one let user to specify own low range under 4G
> + for second kernel instead.
> + 0: to disable low allocation.
> +
> cs89x0_dma= [HW,NET]
> Format: <dma>
>
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--
Thanks
Dave
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