Re: [Patch] Losing many samples when profiling multiple JVMs

Hi,

Anyone has any suggestions?  I hope my patch is included in OProfile-1.1.


Thanks,
Rei Odaira

2015-05-31 22:00 GMT-05:00 大平怜 <[email protected]>:

> Hi,
>
> I found when profiling multiple JVMs, many samples that should have hit
> JITted methods were lost due to no permanent mapping. This was because
> OProfile did not have correct operf_mmap for the JITted code anon regions
> of some of the JVMs. This error can happen as follows:
>
> (1) __handle_mmap_event() creates a new operf_mmap for a small anon region
> of a JVM.
> (2) When another JVM happens to allocate its anon region at the same
> starting virtual address but with a larger size, __handle_mmap_event()
> first searches all_images_map.
> (3) __handle_mmap_event() finds the previously created operf_mmap in
> all_images_map and reuses it, because it checks only filename and
> start_addr.
> (4) As a result, when a sample hits a JITted method that was generated
> between the incorrect end_addr and the actual end
> address, __get_operf_trans() cannot find an appropriate mapping.
>
> The root cause of this problem is that __handle_mmap_event() does not
> check end_addr when searching all_images_map. This should work for a normal
> file, which should have the same size when mapped to different processes,
> but not for anon regions, which can have different sizes in different
> processes. The attached patch will add this check.
>
> More fundamentally, I am wondering what the purpose of all_images_region
> is. I guess it is to reuse operf_mmap structures for more than one
> processes. The file names in all_images_map are stored in absolute paths,
> but they are compared against a file base name in __handle_mmap_event(). As
> a result, this comparison succeeds only for anon and [vdso]. Is this
> intended behavior?
>
>
> Regards,
> Rei Odaira
>

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