Clarification needed for the amount of memory unmapped during imagefile closure.

[Jim Laskey]

An oversight, please file a bug.

— Jim


> On Dec 5, 2018, at 8:37 AM, Alan Bateman <Alan.Bateman at oracle.com> wrote:
> 
> On 05/12/2018 12:26, Jini George wrote:
>> Hello!
>> 
>> I needed a clarification regarding the amount of memory unmapped during imagefile closure in src/java.base/share/native/libjimage/imageFile.cpp.
>> 
>> I noticed that when the "modules" file is opened in ImageFileReader::open(), and the contents are mmap()-ed, the size to be mmap()-ed is derived from map_size().
>> 
>> 399     // Memory map image (minimally the index.)
>> 400     _index_data = (u1*)osSupport::map_memory(_fd, _name, 0, (size_t)map_size());
>> 
>> Which could be _file_size or _index_size, and for 64 bit processes, it would be _file_size. (about 140 MB)
>> 
>> 488     // Retrieve the size of the mapped image.
>> 489     inline u8 map_size() const {
>> 490         return (u8)(memory_map_image ? _file_size : _index_size);
>> 491     }
>> 
>> But when the contents are unmapped in ImageFileReader::close(), the amount of memory unmapped is only _index_size (which is considerably lesser than _file_size).
>> 
>> 427 // Close image file.
>> 428 void ImageFileReader::close() {
>> 429     // Deallocate the index.
>> 430     if (_index_data) {
>> 431         osSupport::unmap_memory((char*)_index_data, _index_size);
>> 432         _index_data = NULL;
>> 433     }
>> 
>> Wanted to check if this is an oversight, or if there is a reason behind this and I am missing something. Shouldn't the amount of memory unmapped be map_size() too ?
> It doesn't look right but needs closer examination. However, I'm curious how you are running into it as it will be completely unmapped when the VM terminates. Is this a tool or test that runs "in process"?
> 
> -Alan