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

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

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.