Re: [dpdk-dev] [PATCH v2] eal: use madvise to exclude unmapped memory from being dumped

["Burakov, Anatoly" <anatoly.burakov@intel.com>]

On 24-Apr-20 12:36 PM, Bruce Richardson wrote:
> On Fri, Apr 24, 2020 at 12:23:44PM +0100, Burakov, Anatoly wrote:
>> On 24-Apr-20 11:50 AM, 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>
>>> ---
>>> V2:
>>> - add support for freebsd.
>>> - when free_seg is called, mark the memory MADV_DONTDUMP.
>>> - when alloc_seg is called, mark the memory MADV_DODUMP.
>>
>> Isn't this v3 now?
>>
>>>
>>>    lib/librte_eal/common/eal_common_memory.c | 26 ++++++++++++++++++++++++++
>>>    lib/librte_eal/linux/eal_memalloc.c       |  6 ++++++
>>>    2 files changed, 32 insertions(+)
>>>
>>> diff --git a/lib/librte_eal/common/eal_common_memory.c b/lib/librte_eal/common/eal_common_memory.c
>>> index cc7d54e0c..83be94a20 100644
>>> --- a/lib/librte_eal/common/eal_common_memory.c
>>> +++ b/lib/librte_eal/common/eal_common_memory.c
>>> @@ -177,6 +177,32 @@ eal_get_virtual_area(void *requested_addr, size_t *size,
>>>    		after_len = RTE_PTR_DIFF(map_end, aligned_end);
>>>    		if (after_len > 0)
>>>    			munmap(aligned_end, after_len);
>>> +
>>> +		/*
>>> +		 * Exclude this pages from a core dump.
>>> +		 */
>>> +#ifdef RTE_EXEC_ENV_LINUX
>>> +		if (madvise(aligned_addr, *size, MADV_DONTDUMP) != 0)
>>> +			RTE_LOG(DEBUG, EAL, "madvise failed: %s\n",
>>> +				strerror(errno));
>>> +#elif RTE_EXEC_ENV_FREEBSD
>>> +		if (madvise(aligned_addr, *size, MADV_NOCORE) != 0)
>>> +			RTE_LOG(DEBUG, EAL, "madvise failed: %s\n",
>>> +				strerror(errno));
>>> +#endif
>>> +	} else {
>>> +		/*
>>> +		 * Exclude this pages from a core dump.
>>> +		 */
>>> +#ifdef RTE_EXEC_ENV_LINUX
>>> +		if (madvise(mapped_addr, map_sz, MADV_DONTDUMP) != 0)
>>> +			RTE_LOG(DEBUG, EAL, "madvise failed: %s\n",
>>> +				strerror(errno));
>>> +#elif RTE_EXEC_ENV_FREEBSD
>>> +		if (madvise(mapped_addr, map_sz, MADV_NOCORE) != 0)
>>> +			RTE_LOG(DEBUG, EAL, "madvise failed: %s\n",
>>> +				strerror(errno));
>>> +#endif
>>>    	}
>>
>> DRY (Don't Repeat Yourself) :) Probably easier to do "if (!unmap) ..." than
>> putting this into two places.
>>
> Can I also suggest putting this at the top of the file:
> #ifdef RTE_EXEC_ENV_LINUX
> #define RTE_DONTDUMP MADV_DONTDUMP
> #elif RTE_EXEC_ENV_FREEBSD
> #define RTE_DONTDUMP MADV_NOCORE
> #else
> #error ....
> #endif
> 
> and thereafter using RTE_DONTDUMP flag and avoiding any #ifdefs inline in
> the code.
> 
+1

-- 
Thanks,
Anatoly