Re: RFC: enhanced memory protection support

[Bean]

On Tue, May 1, 2012 at 1:24 AM, Vladimir 'φ-coder/phcoder' Serbinenko
<address@hidden> wrote:
> On 30.04.2012 17:26, Bean wrote:
>> Hi,
>>
>> While testing network function in efi mode, I've found several memory
>> leak related to fragmentation, but there is still some memory problem
>> that's very tricky to locate. For example, you can run testspeed on a
>> large file several times in a row and it could show the memory error.
>> Since network condition are very difficult to reproduce, I have to
>> look at the source of this issue, memory allocation. Currently it has
>> mm_debug option that could print out file and line number of each
>> memory call, but it's quite useless since we can't find the relevant
>> informaton with full screen of prints.
>> Here are some of my ideas for enhanced memory protection support:
>>
>> 1, when we allocate memory, we append some information at the end of
>> the buffer, which include filename, lineno of caller, and tag to
>> indicate what is used for and some padding to detect memory overwrite
>> problem.
>>
>> 2. add a command to print the current memory list with extended
>> information, this can be used to find memory leaks.
>>
>> 3. it's also a good idea to run the memory check in automated test to
>> locate potential issue.
> This is pretty easy to do leveraging some of the code I did for POSIX
> support. But:
> - Due to additional time and space required it should be done only when
> mm-debug is enabled.
> - The additional data has to be stored before rather than after the
> range since we store all the info before.
> - Integrating with automated tests isn't that easy since some memory is
> intentionally never freed i.a. disk cache or otherwise in use (i.a.
> terminal). We need exceptions for those.
> I have half-working patch, just needs few fixes.

Hi,

Some thoughts about this:

We can assign a sequence id for each allocated memory, then we can
search memory allocated from point A to B. This can be used to skip
memory allocated during initialization stage.

We can use special tag for memory that would stick around, for
example, the *prefix: *cache, *fs, *term, etc, then we can skip them
in auto tests.

-- 
Best wishes
Bean