On 23-Apr-20 4:43 PM, Li Feng wrote:
Avoid dump all mapped memory to a core dump file when crash.
Otherwise it will very large and it's hard to analyze with gdb.

In my test, it will dump 128GiB memory to a core dump file when integrated
to spdk with default configuration.

Suggested rewording:

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 <fen...@smartx.com>
---
  lib/librte_eal/common/eal_common_memory.c | 14 ++++++++++++++
  1 file changed, 14 insertions(+)

diff --git a/lib/librte_eal/common/eal_common_memory.c 
b/lib/librte_eal/common/eal_common_memory.c
index cc7d54e0c..2d9564b28 100644
--- a/lib/librte_eal/common/eal_common_memory.c
+++ b/lib/librte_eal/common/eal_common_memory.c
@@ -177,6 +177,20 @@ 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.
+                */
+               if (madvise(aligned_addr, *size, MADV_DONTDUMP) != 0)
+                       RTE_LOG(WARNING, EAL, "Madvise with MADV_DONTDUMP failed: 
%s\n",
+                               strerror(errno)); > +        } else {
+               /*
+                * Exclude this pages from a core dump.
+                */
+               if (madvise(mapped_addr, map_sz, MADV_DONTDUMP) != 0)
+                       RTE_LOG(WARNING, EAL, "Madvise with MADV_DONTDUMP failed: 
%s\n",
+                               strerror(errno));
        }
return aligned_addr;


For the contents of this patch,

Acked-by: Anatoly Burakov <anatoly.bura...@intel.com>

However, even though this is good to have, after some more thought, i believe the fix is incomplete, because this is not the only place we're reserving anonymous memory. We're also doing so in `eal_memalloc.c:free_seg()`, so an `madvise()` call should also be added there.

@David, now that i think of it, the PROT_NONE patch also was incomplete, as we only set PROT_NONE to memory that's initially reserved, but not when it's unmapped and returned back to the pool of anonymous memory. So, eal_memalloc.c should also remap anonymous memory with PROT_NONE.

@Li Feng, would you be so kind as to provide a patch replacing PROT_READ with PROT_NONE in eal_memalloc.c as well? Thank you very much!

--
Thanks,
Anatoly

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