RE: [PATCH v2] makedumpfile: exclude pages that are logically offline

[Kazuhito Hagio <k-hagio@ab.jp.nec.com>]

> Linux marks pages that are logically offline via a page flag (map count).
> Such pages e.g. include pages infated as part of a balloon driver or
> pages that were not actually onlined when onlining the whole section.
> 
> While the hypervisor usually allows to read such inflated memory, we
> basically read and dump data that is completely irrelevant. Also, this
> might result in quite some overhead in the hypervisor. In addition,
> we saw some problems under Hyper-V, whereby we can crash the kernel by
> dumping, when reading memory of a partially onlined memory segment
> (for memory added by the Hyper-V balloon driver).
> 
> Therefore, don't read and dump pages that are marked as being logically
> offline.
> 
> Signed-off-by: David Hildenbrand <david@redhat.com>

Thanks for the v2 update.
I'm going to merge this patch after the kernel patches are merged
and it tests fine with the kernel.

Kazu

> ---
> 
> v1 -> v2:
> - Fix PAGE_BUDDY_MAPCOUNT_VALUE vs. PAGE_OFFLINE_MAPCOUNT_VALUE
> 
>  makedumpfile.c | 34 ++++++++++++++++++++++++++++++----
>  makedumpfile.h |  1 +
>  2 files changed, 31 insertions(+), 4 deletions(-)
> 
> diff --git a/makedumpfile.c b/makedumpfile.c
> index 8923538..a5f2ea9 100644
> --- a/makedumpfile.c
> +++ b/makedumpfile.c
> @@ -88,6 +88,7 @@ mdf_pfn_t pfn_cache_private;
>  mdf_pfn_t pfn_user;
>  mdf_pfn_t pfn_free;
>  mdf_pfn_t pfn_hwpoison;
> +mdf_pfn_t pfn_offline;
> 
>  mdf_pfn_t num_dumped;
> 
> @@ -249,6 +250,21 @@ isHugetlb(unsigned long dtor)
>                      && (SYMBOL(free_huge_page) == dtor));
>  }
> 
> +static int
> +isOffline(unsigned long flags, unsigned int _mapcount)
> +{
> +	if (NUMBER(PAGE_OFFLINE_MAPCOUNT_VALUE) == NOT_FOUND_NUMBER)
> +		return FALSE;
> +
> +	if (flags & (1UL << NUMBER(PG_slab)))
> +		return FALSE;
> +
> +	if (_mapcount == (int)NUMBER(PAGE_OFFLINE_MAPCOUNT_VALUE))
> +		return TRUE;
> +
> +	return FALSE;
> +}
> +
>  static int
>  is_cache_page(unsigned long flags)
>  {
> @@ -2287,6 +2303,8 @@ write_vmcoreinfo_data(void)
>  	WRITE_NUMBER("PG_hwpoison", PG_hwpoison);
> 
>  	WRITE_NUMBER("PAGE_BUDDY_MAPCOUNT_VALUE", PAGE_BUDDY_MAPCOUNT_VALUE);
> +	WRITE_NUMBER("PAGE_OFFLINE_MAPCOUNT_VALUE",
> +		     PAGE_OFFLINE_MAPCOUNT_VALUE);
>  	WRITE_NUMBER("phys_base", phys_base);
> 
>  	WRITE_NUMBER("HUGETLB_PAGE_DTOR", HUGETLB_PAGE_DTOR);
> @@ -2687,6 +2705,7 @@ read_vmcoreinfo(void)
>  	READ_SRCFILE("pud_t", pud_t);
> 
>  	READ_NUMBER("PAGE_BUDDY_MAPCOUNT_VALUE", PAGE_BUDDY_MAPCOUNT_VALUE);
> +	READ_NUMBER("PAGE_OFFLINE_MAPCOUNT_VALUE", PAGE_OFFLINE_MAPCOUNT_VALUE);
>  	READ_NUMBER("phys_base", phys_base);
>  #ifdef __aarch64__
>  	READ_NUMBER("VA_BITS", VA_BITS);
> @@ -6041,6 +6060,12 @@ __exclude_unnecessary_pages(unsigned long mem_map,
>  		else if (isHWPOISON(flags)) {
>  			pfn_counter = &pfn_hwpoison;
>  		}
> +		/*
> +		 * Exclude pages that are logically offline.
> +		 */
> +		else if (isOffline(flags, _mapcount)) {
> +			pfn_counter = &pfn_offline;
> +		}
>  		/*
>  		 * Unexcludable page
>  		 */
> @@ -7522,7 +7547,7 @@ write_elf_pages_cyclic(struct cache_data *cd_header, struct cache_data *cd_page)
>  	 */
>  	if (info->flag_cyclic) {
>  		pfn_zero = pfn_cache = pfn_cache_private = 0;
> -		pfn_user = pfn_free = pfn_hwpoison = 0;
> +		pfn_user = pfn_free = pfn_hwpoison = pfn_offline = 0;
>  		pfn_memhole = info->max_mapnr;
>  	}
> 
> @@ -8804,7 +8829,7 @@ write_kdump_pages_and_bitmap_cyclic(struct cache_data *cd_header, struct cache_d
>  		 * Reset counter for debug message.
>  		 */
>  		pfn_zero = pfn_cache = pfn_cache_private = 0;
> -		pfn_user = pfn_free = pfn_hwpoison = 0;
> +		pfn_user = pfn_free = pfn_hwpoison = pfn_offline = 0;
>  		pfn_memhole = info->max_mapnr;
> 
>  		/*
> @@ -9749,7 +9774,7 @@ print_report(void)
>  	pfn_original = info->max_mapnr - pfn_memhole;
> 
>  	pfn_excluded = pfn_zero + pfn_cache + pfn_cache_private
> -	    + pfn_user + pfn_free + pfn_hwpoison;
> +	    + pfn_user + pfn_free + pfn_hwpoison + pfn_offline;
>  	shrinking = (pfn_original - pfn_excluded) * 100;
>  	shrinking = shrinking / pfn_original;
> 
> @@ -9763,6 +9788,7 @@ print_report(void)
>  	REPORT_MSG("    User process data pages : 0x%016llx\n", pfn_user);
>  	REPORT_MSG("    Free pages              : 0x%016llx\n", pfn_free);
>  	REPORT_MSG("    Hwpoison pages          : 0x%016llx\n", pfn_hwpoison);
> +	REPORT_MSG("    Offline pages           : 0x%016llx\n", pfn_offline);
>  	REPORT_MSG("  Remaining pages  : 0x%016llx\n",
>  	    pfn_original - pfn_excluded);
>  	REPORT_MSG("  (The number of pages is reduced to %lld%%.)\n",
> @@ -9790,7 +9816,7 @@ print_mem_usage(void)
>  	pfn_original = info->max_mapnr - pfn_memhole;
> 
>  	pfn_excluded = pfn_zero + pfn_cache + pfn_cache_private
> -	    + pfn_user + pfn_free + pfn_hwpoison;
> +	    + pfn_user + pfn_free + pfn_hwpoison + pfn_offline;
>  	shrinking = (pfn_original - pfn_excluded) * 100;
>  	shrinking = shrinking / pfn_original;
>  	total_size = info->page_size * pfn_original;
> diff --git a/makedumpfile.h b/makedumpfile.h
> index f02f86d..e3a2b29 100644
> --- a/makedumpfile.h
> +++ b/makedumpfile.h
> @@ -1927,6 +1927,7 @@ struct number_table {
>  	long    PG_hwpoison;
> 
>  	long	PAGE_BUDDY_MAPCOUNT_VALUE;
> +	long	PAGE_OFFLINE_MAPCOUNT_VALUE;
>  	long	SECTION_SIZE_BITS;
>  	long	MAX_PHYSMEM_BITS;
>  	long    HUGETLB_PAGE_DTOR;
> --
> 2.17.2
>