Re: [dpdk-dev] [PATCH v5] eal: use madvise to exclude unmapped memory from being dumped

[Bruce Richardson <bruce.richardson@intel.com>]

On Fri, Apr 24, 2020 at 08:53:11PM +0800, Li Feng wrote:
> Currently, even though memory is mapped with PROT_NONE, this does not
> cause it to be excluded from core dumps. This is counter-productive,
> because in a lot of cases, this memory will go unused (e.g. when the
> memory subsystem preallocates VA space but hasn't yet mapped physical
> pages into it).
> 
> Use `madvise()` call with MADV_DONTDUMP parameter to exclude the
> unmapped memory from being dumped.
> 
> Signed-off-by: Li Feng <fengli@smartx.com>
> ---
> v5:
> - fix a code style.
> 
> V4:
> - simplify the code;
> - remove the undo code in V3;
> 
> V3:
> - add support for freebsd.
> - when free_seg is called, mark the memory MADV_DONTDUMP.
> - when alloc_seg is called, mark the memory MADV_DODUMP.
> 
>  lib/librte_eal/common/eal_common_memory.c | 17 +++++++++++++++++
>  lib/librte_eal/linux/eal_memalloc.c       |  3 +++
>  2 files changed, 20 insertions(+)
> 
> diff --git a/lib/librte_eal/common/eal_common_memory.c b/lib/librte_eal/common/eal_common_memory.c
> index cc7d54e0c..161e49825 100644
> --- a/lib/librte_eal/common/eal_common_memory.c
> +++ b/lib/librte_eal/common/eal_common_memory.c
> @@ -40,6 +40,14 @@
>  static void *next_baseaddr;
>  static uint64_t system_page_sz;
>  
> +#ifdef RTE_EXEC_ENV_LINUX
> +#define RTE_DONTDUMP MADV_DONTDUMP
> +#elif RTE_EXEC_ENV_FREEBSD
> +#define RTE_DONTDUMP MADV_NOCORE
> +#else
> +#error "madvise doesn't support this OS"
> +#endif
> +

You forgot to use RTE_DONTDUMP in place of MADV_DONTDUMP below.

>  #define MAX_MMAP_WITH_DEFINED_ADDR_TRIES 5
>  void *
>  eal_get_virtual_area(void *requested_addr, size_t *size,
> @@ -179,6 +187,15 @@ eal_get_virtual_area(void *requested_addr, size_t *size,
>  			munmap(aligned_end, after_len);
>  	}
>  
> +	if (!unmap) {
> +		/*
> +		 * Exclude this pages from a core dump.
> +		 */
> +		if (madvise(aligned_addr, *size, MADV_DONTDUMP) != 0)
> +			RTE_LOG(DEBUG, EAL, "madvise failed: %s\n",
> +				strerror(errno));
> +	}
> +
>  	return aligned_addr;
>  }
>  
> diff --git a/lib/librte_eal/linux/eal_memalloc.c b/lib/librte_eal/linux/eal_memalloc.c
> index af6d0d023..f628e0991 100644
> --- a/lib/librte_eal/linux/eal_memalloc.c
> +++ b/lib/librte_eal/linux/eal_memalloc.c
> @@ -687,6 +687,9 @@ free_seg(struct rte_memseg *ms, struct hugepage_info *hi,
>  		return -1;
>  	}
>  
> +	if (madvise(ms->addr, ms->len, MADV_DONTDUMP) != 0)
> +		RTE_LOG(DEBUG, EAL, "madvise failed: %s\n", strerror(errno));
> +
>  	exit_early = false;
>  
>  	/* if we're using anonymous hugepages, nothing to be done */
> -- 
> 2.11.0
> 
> 
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