[Crash-utility] [PATCH] Update for the "kmem -n" option on Linux 5.3-rc1 and later kernels

[Dave Anderson]

Hi Kazu,

Do you have a sample 5.3-rc1 vmlinux/vmcore pair that I can test this with?
You can send it to me offline.

Thanks,
  Dave


----- Original Message -----
> Update for the "kmem -n" option on Linux 5.3-rc1 and later kernels that
> contain commit 326e1b8f83a4318b09033ef754f40c785aed5e68, titled
> "mm/sparsemem: introduce a SECTION_IS_EARLY flag". With this patch,
> the option displays a new state "E" for the flag, instead of printing
> incorrect mem_map addresses.
> 
> Also update the confusing comment with the one from kernel commit
> def9b71ee651a6fee93a10734b94f93a69cdb2d4, titled "include/linux/mmzone.h:
> fix explanation of lower bits in the SPARSEMEM mem_map pointer".
> 
> Signed-off-by: Kazuhito Hagio <k-hagio at ab.jp.nec.com>
> ---
>  help.c   |  4 ++--
>  memory.c | 17 ++++++++++++++---
>  2 files changed, 16 insertions(+), 5 deletions(-)
> 
> diff --git a/help.c b/help.c
> index d5940f789ffd..a5218a701c01 100644
> --- a/help.c
> +++ b/help.c
> @@ -6597,8 +6597,8 @@ char *help_kmem[] = {
>  "            the cumulative, vm_event_states counter values if they exist.",
>  "        -n  display memory node, memory section, and memory block data",
>  "            and state; the state of each memory section state is encoded",
> -"            as \"P\", \"M\" and/or \"O\", meaning SECTION_MARKED_PRESENT,",
> -"            SECTION_HAS_MEM_MAP and SECTION_IS_ONLINE.",
> +"            as \"P\", \"M\", \"O\" and/or \"E\", meaning
> SECTION_MARKED_PRESENT,",
> +"            SECTION_HAS_MEM_MAP, SECTION_IS_ONLINE and SECTION_IS_EARLY.",
>  "        -z  displays per-zone memory statistics.",
>  "        -o  displays each cpu's offset value that is added to per-cpu
>  symbol",
>  "            values to translate them into kernel virtual addresses.",
> diff --git a/memory.c b/memory.c
> index 327e5355ec9c..ac7e73679405 100644
> --- a/memory.c
> +++ b/memory.c
> @@ -17154,13 +17154,22 @@ nr_to_section(ulong nr)
>  
>  /*
>   * We use the lower bits of the mem_map pointer to store
> - * a little bit of information.  There should be at least
> - * 3 bits here due to 32-bit alignment.
> + * a little bit of information.  The pointer is calculated
> + * as mem_map - section_nr_to_pfn(pnum).  The result is
> + * aligned to the minimum alignment of the two values:
> + *   1. All mem_map arrays are page-aligned.
> + *   2. section_nr_to_pfn() always clears PFN_SECTION_SHIFT
> + *      lowest bits.  PFN_SECTION_SHIFT is arch-specific
> + *      (equal SECTION_SIZE_BITS - PAGE_SHIFT), and the
> + *      worst combination is powerpc with 256k pages,
> + *      which results in PFN_SECTION_SHIFT equal 6.
> + * To sum it up, at least 6 bits are available.
>   */
>  #define SECTION_MARKED_PRESENT	(1UL<<0)
>  #define SECTION_HAS_MEM_MAP	(1UL<<1)
>  #define SECTION_IS_ONLINE	(1UL<<2)
> -#define SECTION_MAP_LAST_BIT	(1UL<<3)
> +#define SECTION_IS_EARLY	(1UL<<3)
> +#define SECTION_MAP_LAST_BIT	(1UL<<4)
>  #define SECTION_MAP_MASK	(~(SECTION_MAP_LAST_BIT-1))
>  
>  
> @@ -17257,6 +17266,8 @@ fill_mem_section_state(ulong state, char *buf)
>  		bufidx += sprintf(buf + bufidx, "%s", "M");
>  	if (state & SECTION_IS_ONLINE)
>  		bufidx += sprintf(buf + bufidx, "%s", "O");
> +	if (state & SECTION_IS_EARLY)
> +		bufidx += sprintf(buf + bufidx, "%s", "E");
>  }
>  
>  void
> --
> 2.18.1
> 
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